524 Colour Reproduction in Electronic Imaging Systems No significant differences in the dark steps of the greyscale are perceived, possibly indicating the same gamma law correction had been applied during image capture, irrespective of the colour mode chosen. (One might have expected the difference in the gamma law for the sRGB and Adobe RGB colour space specifications to show up in untagged files as slight differences in the dark steps of the greyscale.) 29.4 Colour Managing Raw Files Loading Raw files into Photoshop automatically opens the Adobe Camera Raw plugin. This is another powerful application for photographers, providing tools that go beyond those described in the following paragraphs, since these are limited to describing only the colour-related parameters. There are however many excellent books available on the broader use of Camera Raw, one being ‘The Digital Negative’ (Schewe, 2013). The RGB components of a raw file have not yet been processed to take on the characteristics of a particular colour space; however, the components will have been shaped by the proprietary characteristics of the capture responses of the optical components of the camera, including those of the image sensor. Furthermore, the RGB components are linear, that is, unlike the JPEG file components they are not gamma corrected. Thus in colour management terms the job of Camera Raw is to transform the proprietary colour space into a defined colour space and embed a matching profile in order that it may be properly colour managed in subsequent stages of the workflow. Attempting to load a raw file into Photoshop will automatically activate AdobeRaw the image will be converted into the colour space used the last time the application was activated. Figure 29.16 illustrates the screen display when loading the Camera Raw file containing the ColorChecker chart. The very small blue lettering at the centre bottom of the display gives the current working space of Camera Raw together with the image size. It reads: ‘ProPhoto RGB; 16 bit; 2560 by 1920 (4.9MP); 300 ppi’. Clicking on this information brings up the Workflow Options display illustrated in Figure 29.17. Figure 29.16 The ColorChecker chart in Camera Raw.
Colour Management in the Desktop Workflow 525 Figure 29.17 Selecting the colour space in Camera Raw. As Figure 29.17 illustrates Adobe Raw offers the option of four working colour spaces: Adobe RGB, ColorMatch RGB, ProPhoto RGB and sRGB. Our aim is to minimise any potential gamut clipping or mapping, so the natural choice is ProPhoto RGB. The raw file carries a good deal of metadata which defines many of the parameter settings of the camera at the time the image was captured, including ‘Exposure’ and ‘Contrast’. All of these adjustable parameters are made available to the user in Camera Raw. Normally for this exercise all adjustments are set at the default zero position when the file is opened and any adjustment required should be limited to the following: r Set Exposure to just not clip peak levels on the histogram. chip of the greyscale of the r Use the White Balance Tool to white balance the white ColorChecker chart. The image file is now ready for loading into Photoshop, which is achieved by selecting the ‘Open Copy’ button at the lower right of the screen illustrated in Figure 29.16, (‘Open Image’ in later versions). If the working colour spaces of Camera Raw and Photoshop match, this action will load the image into Photoshop, if there is not a match Photoshop will provide the operator with action options as detailed in the next section.
526 Colour Reproduction in Electronic Imaging Systems 29.5 Matching the Display to the Scene This section provides a review of the Photoshop workflow, stage by stage from opening the file to appraising the match between the display and the scene, that being the original ColorChecker chart. 29.5.1 Preparations for Exercising the Workflow In order to establish with confidence the options provided and the actions to be taken by Photoshop when opening files, it is very useful to have a range of files available with identical images but with different capture characteristics. This was one of the main reasons the range of files described in Section 28.4 were captured, in order that they may be used to good effect in exploring the options and actions required when opening files in Photoshop. This section is given over to describing these procedures. Figure 29.18 The settings in the Color Management Policies panel. As a reminder Figure 29.18 illustrates the default settings of the ‘Color Management Policies’ panel described in Section 29.2; however, these settings will be varied in the following descriptions as files are opened in Photoshop to provide the opportunity of becoming familiar with the Photoshop approach to these tasks. Subject to the appropriate ‘Ask When Opening’ boxes being ticked, the setting in the RGB box does not alone determine which option panels are displayed when opening files. If the RGB box is set to ‘Convert to Working RGB’ and the appropriate ‘Ask’ box is not ticked, then conversion of non-matching files to the working space will take place automatically after the first conversion, subject to the option panel that first appears being appropriately ticked. 29.5.2 Opening Files in Photoshop Having set the colour management parameters for Photoshop we can start to open our files but before doing so we should be aware of the following: r Unavoidably, several different situations may present themselves when opening a file in r Photoshop which initially can appear somewhat daunting. the right choice of settings, However, Photoshop is very good at assisting the user to make whether it is to just remind one of the current working colour space or to guide the uninitiated to the correct choice.
Colour Management in the Desktop Workflow 527 r This is a straightforward matter if the profile space of the input file, that is, from the camera r or scanner, and the working space of Photoshop match. selection is made and which If they do not match, then the action will depend upon which boxes are ticked in the ‘Colour Management Policies’ panel. The following sub-sections describe the result of selecting in turn the various options in the Edit→Color Settings→Color Management Policies→ RGB: settings from the menu system. 29.5.2.1 Color Management Policies →RGB Off On the Color Management Policies panel select the RGB: to Off. Use File →Open to load the tagged ‘Minolta A1 Natural sRGB’ file. If the ‘Working Space RGB’ had been set to sRGB, the file would open with no ‘Mismatch’ panel being displayed. Figure 29.19 Opening option – colour management off. As there is no match, the Mismatch panel appears as illustrated in Figure 29.19, which always illustrates the embedded profile and the working profile in order to highlight the details of the mismatch. Since the ‘Off’ option had been selected, Photoshop assumes colour management is not required and therefore defaults to offering the ‘Discard profile’ option. Should a file with no embedded profile be opened in this situation, then Photoshop places it straight into the working space with no questions asked.
528 Colour Reproduction in Electronic Imaging Systems However, should the user wish to override the ‘Off’ selection, the option is provided to either use the embedded profile or convert the image to the working space. 29.5.2.2 Color Management Policies →RGB Colour Management Operational – Embedded Profile If ‘Settings’ is set to an operational ‘Colour Management’ configuration, and an attempt is made to open a file with an embedded profile, which matches the selected working colour space, then the file will again open with no questions asked. However, if there is a mismatch between the two environments then Photoshop will present the same panel as the one previously but with a different default option selected, the actual selection depending upon whether Color Management Policies’ was set for ‘Preserve’ or ‘Convert’ as illustrated in Figure 29.20. Figure 29.20 Opening option – colour management on – embedded profile. If one is working simultaneously with a number of files, with different embedded profiles, then it makes sense to convert them all to the chosen working space. However, if this is a single image file there is little advantage in either option, subject to the embedded working space being within the limits of the working colour space. In these circumstances it may be convenient to place the file effectively into a temporary dedicated working space to match the embedded profile. In converting a file, the embedded profile is amended to match the working space, so care should be taken when saving the file, if one wishes to retain the original file with the original embedded profile.
Colour Management in the Desktop Workflow 529 29.5.2.3 Color Management Policies→RGB Colour Management Operational – no Embedded Profile 1 Open the ‘Epson Scanner – Target Adobe RGB’ file which has no profile but was known to be encoded to the Adobe RGB specification. Figure 29.21 Opening option – colour management on – no profile. This presents the user with an interesting range of options as shown in Figure 29.21. Assuming that colour management is on, then it is unlikely that the first option would be selected. Often, as in the case illustrated, although there is no embedded profile it is known that the file was created with a specified target colour space, in this case Adobe RGB. The second option is inappropriate since it is essential to assign a profile which matches the encoded colour space of the file, which is Adobe RGB. Therefore the third option is selected and in addition, the arrow is activated to open the range of colour space options and the Adobe RGB colour space is selected. If the ‘and then convert document to working RGB’ box is ticked, the image will be converted to the working colour space and a new profile matching the working space will be assigned and will be embedded should the file be saved. 29.5.2.4 Viewing the Open File The name of the encoded colour space of an open file is displayed on the screen together with the number of bits per digital colour, its positioning depending upon the Window arrangement. For what might be defined as the ‘normal’ mode with the image of one file only displayed, accessed via Window →Arrange → Consolidate All to Tabs, the colour space name is displayed on the left-hand side of the Widows frame. If more than one image is displayed using Windows →Arrange →Float All in Windows, the name is located in the lower left-hand side of the image frame. If the file is untagged, the name is given as ‘Untagged’.
530 Colour Reproduction in Electronic Imaging Systems 29.5.3 Managing Files and Profiles within Photoshop So now we know how to deal with opening files into Photoshop, how do we deal with the options available for managing them once they are safely opened? Photoshop provides the facility to manage files as they are opened in Photoshop but it may subsequently become necessary to change the characteristics, either by changing the working space from RGB to CMYK or assigning or changing a profile. 29.5.3.1 RGB or CMYK Mode Determining whether to operate in RGB or CMYK mode is achieved by selecting Image →Mode which will provide option panels as illustrated in Figure 29.22. Figure 29.22 Colour mode selection. The menu selection shown on this screenshot offers three generic types of working space for the file to operate within; ‘RGB Color’, ‘CMYK Color’ and ‘Lab Color’, and provides for a mathematical transform between them.
Colour Management in the Desktop Workflow 531 The particular RGB or CMYK colour encoding space associated with these options was set in the ‘Colour Settings’ panel as described in Section 29.2.2.3. Image chromaticities which fall within the gamut of all three colour spaces will be displayed identically, irrespective of the working space selected. However if, as with the colour chart, some chromaticities fall outside of the CMYK colour space, then the selection of that space will cause a significant reduction in the displayed saturation of the associated colour patch, caused by the gamut clipping or gamut mapping operation. This is a permanent loss; switching back to RGB will not restore the original component levels. The primary working space of interest to us is the default ‘RGB Color’ space. 29.5.3.2 Managing the Profiles of Open Files As we have seen, options are available on opening a file to either ignore the option of assigning a profile to an untagged file or adopting or converting the profile associated with the file. These same options are available to colour managing open files. The ‘Assign Profile’ and ‘Convert to Profile’ commands may be found towards the bottom of the ‘Edit’ menu, appropriately beneath ‘Colour Settings’. The following examples illustrate how these commands may be used. It is assumed for this exercise that we will use the untagged files generated by the Epson scanner as described in Section 28.4, where each of the three files captured were encoded with different image colour spaces as listed in Table 29.1 and described in Section 24.2. Table 29.1 Epson scanner untagged files Source Colour space Profile File Scanner sRGB Untagged JPEG Scanner Adobe RGB Untagged JPEG Scanner Wide gamut RGB Untagged JPEG Non-profiled files with no identification may be properly identified and profiled, and if required converted to the system working space. The aim of this example is to show that after non-profiled files have been loaded with no identification at open time, they may subsequently be properly identified and profiled and if required converted to the system working space. The results from undertaking this exercise provide a bonus, in as much as they illustrate in a profound manner the justification of, and exemplary workings of, ICC-based colour management. For these tests we will first ensure that sRGB is selected as the Photoshop default working colour space (see Section 29.2.2.3). As the file is opened, Photoshop immediately determines there is no embedded profile and asks how one would wish to proceed. 29.5.3.3 Opening the Untagged Files Opening an untagged file will cause Photoshop to display the panel illustrated in Figure 29.23.
532 Colour Reproduction in Electronic Imaging Systems Figure 29.23 Opening untagged files. Select the ‘Leave as is’ option and in turn open all three of the untagged files. When all three untagged files have been loaded, Photoshop is arranged to display the three files simultaneously by using Window→Arrange→Float All in Windows. After some juggling and rearranging the three files will be displayed as illustrated in Figure 29.24, a very instructive display. It will be noted that in terms of saturation three very different looking images appear. Unfortunately in this capture the lettering in the title bar at the top of each image frame is barely legible; however, the files are laid out in order of colour encoding spaces from the top left, with image titles ‘Wide Gamut RGB’, ‘Adobe RGB’ and ‘sRGB’, respectively; also in the title bar, ‘#’ has been added to the file name to indicate there is no confirmation of a match of the capture and the working profiles. Each image is also labelled as ‘Untagged RGB (8bpc)’ in the lower title bar. Before progressing further, it may be instructive to discuss why it is that those images captured with the larger gamuts are displayed with decreasing saturation. The component code values, in for example, the Wide Gamut RGB file, are expecting to control satu- rated primaries and therefore have a lower value than the corresponding values in the sRGB file. However in this display, because there is no profile present to tell Photoshop how to handle the file, these lower values are controlling the working profile sRGB pri- maries and the result will therefore be a desaturated display. Thus the only one of the three files to be displayed correctly is the sRGB file, since by default that is also the working colour space. The next step is to assign appropriate matching profiles to each of these files.
Colour Management in the Desktop Workflow 533 Figure 29.24 Display of the three untagged scanner files. 29.5.3.4 Assigning Profiles to the Untagged Files Using Edit →Assign Profile, the screenshot illustrated in Figure 29.25 appears. Figure 29.25 Assigning a profile to an untagged file. We can now assign the appropriate matching profile, respectively to each of the images in turn by highlighting the ‘Profile:’ button and selecting the appropriate colour space from the drop-down list. As each image is selected, one may click alternately on the ‘Preview’ box and see the effect of applying the profile to the image.
534 Colour Reproduction in Electronic Imaging Systems Figure 29.26 The three originally untagged files with appropriately assigned profiles. The result of assigning the profiles is illustrated in Figure 29.26. It will be noted that the sRGB targeted image does not change but the presence of the appropriate profiles causes the other two images to be processed such that they now form a perfect match with the sRGB image. The name of the new profile now appears underneath each displayed image on the left-hand side. Thus although we now have matching images, each is displayed in its assigned working space (as opposed to the system working space) and if these files were to be saved, and these new files reopened, it would be found that each now had an embedded profile which matched its original targeted colour space. It will also be noted that where the working space does not match the system working space the document’s title bar working space indicator has changed from RGB# to RGB∗. 29.5.3.5 Converting Profiles The two non-sRGB image files can be converted into sRGB files by using the ‘Edit →Convert to Profile’ menu command which will cause the panel illustrated in Figure 29.27 to appear. Convert both the ‘Wide Gamut RGB’ and ‘Adobe RGB’ images to the ‘sRGB’ working space. After conversion the display will appear as illustrated in Figure 29.28.
Colour Management in the Desktop Workflow 535 Figure 29.27 Converting the images to the working colour space. Figure 29.28 The three original un-tagged images converted to the working colour space.
536 Colour Reproduction in Electronic Imaging Systems It will be noted that all three images still match one another but the colour space name for each of the images is now sRGB, and, if saved at this stage, they will be saved with an embedded sRGB profile. 29.5.3.6 Correcting an Incorrectly Opened Profile Let us assume a non-profiled ‘Wide Gamut RGB’ file is loaded into sRGB working space and has been incorrectly assigned an sRGB profile. r Use ‘Assign Profile’ to provide the file with the correct ‘Wide Gamut RGB’ profile. r If required, now use ‘Convert to Profile’ to convert the file to sRGB. It is very easy to open a non-profiled file into the working colour space as a default – only to find subsequently that clearly the image was captured with a colour space which did not match the working space. Photoshop enables one to correct the situation without having to reopen the original file. Assuming that the ‘Epson Scanner – Target Wide Gamut’ file has been inadvertently opened into the sRGB system working space and is now associated with an sRGB profile. The correction procedure is similar to that above: first select ‘Assign Profile’ and then select the colour space it is assumed was used as the target colour space during capture – in this case the Wide Gamut RGB colour space. Photoshop will now reprocess the image in accordance with the new colour space, edit the profile to Wide Gamut RGB and display the image correctly in its own Wide Gamut RGB working space. If it is now required to convert the image to an sRGB colour space then this may be achieved by selecting ‘Convert to Profile’ and then selecting the sRGB colour space. Photoshop reprocesses the data to sRGB and also edits the associated profile to sRGB. 29.5.4 Image Adjustment in Photoshop In order to exercise colour management thoroughly we will undertake the absolute minimum of adjustment of the reference files, by firstly selecting Image→/Adjustments→ Levels which will place the ‘Levels’ adjustment panel on screen as illustrated in Figure 29.29. r The ‘Set White Point’ – sets the colour balance of the white chip of the chart greyscale to neutral and automatically makes it equal to a digital code level 255; prior to adjustment the r RGB levels were equal at a level of 251. are not quite neutral. Optionally the ‘Set Grey The neutral chips of the ColorChecker chart r Point’ – may be used to set the colour balance of the mid grey. Do not adjust the level of the black step of the chart. To set the white point, click on the ‘Set White Point’ picker and then click on the white of the greyscale. To colour balance any transfer characteristic greyscale irregularities click on the middle ‘Set Grey Point’ picker and then click on the third grey chip from zero. That is the limit of any adjustment to the image.
Colour Management in the Desktop Workflow 537 Figure 29.29 White balance adjustment. There is not always the opportunity to place a white card, or even better a greyscale, in the scene. Nevertheless, more often than not there are whites in the scene which can be used to obtain this very critical white balance using this technique. Most modern cameras track greyscale reasonably well but if it is clear that having set the white point the greys are not neutral then sometimes finding a grey in the scene and using the middle picker can improve the situation. (Care must be taken on whites in shadows since these are lit by what may be a totally blue sky and white balancing on a blue shadow will lead to disastrous results). Setting the white and grey balance is the limit of any adjustment to the image. The adjusted images of the three files are with minor variations virtually of the same appearance as those of the untagged images illustrated in Figure 29.28 and illustrated in the next section. 29.5.4.1 Appraising the Match of the Scene with the Display The appraisal of the matches between the scene and the display of the various exercise files was undertaken on a wide gamut display, profiled using the X-rite iPro spectrum photometer and the i1 Profiler application. The screen was set to a highlight luminance of 100 nits, at a white point of D65 and a gamma of 2.2. The ColorChecker chart was evenly illuminated with adjustable level D65 fluorescent lamps and the highlight level set to subjectively match the white chip of the chart with the white chip of the displayed chart.
538 Colour Reproduction in Electronic Imaging Systems In an ideal situation there should be no perceptible difference between the rendered images of the six exercise files, however although the images are ‘acceptably’ close there are relatively minor differences and therefore of course differences when each is compared to the original scene. Unfortunately it is not possible to illustrate in this book precisely how the matches compare for the following reasons: r In capturing an image of the original and the display together for an illustration in the book r the limitations of the capture camera will be imposed on the image. for the reasons In printing the image in the book the colour will inevitably be compromised explained in Chapter 23. By a small margin the best visual match between the displayed image and the original chart was the raw camera capture illustrated in Figure 29.30. In view of the limitations detailed above regarding the reproduction of this image in the book, I will add a few subjective comments regarding the critical appraisal of the match of the image to the original: r At first sight there appeared to be a very good match in all respects. the exception was the r Of the top two rows of samples the matches were generally excellent; r orange sample which was slightly over saturated. the yellow, magenta and cyan were Of the primaries, the blue was noticeably desaturated, very slightly desaturated, the red was slightly too bright and the green was an excellent match. Figure 29.30 Camera Raw screenshot of the ColorChecker chart.
Colour Management in the Desktop Workflow 539 Figure 29.31 The camera match of the original and displayed image. In summary, on the basis of a subjective appraisal only, the results of this exercise indicate that colour management is working well in producing a very good match between original and display. Figure 29.31 is an un-retouched photo of the original chart with the screen showing the camera Adobe RGB image. Admittedly this is not a very scientific approach, with the result being open to criticisms of metamerism, etc. Nevertheless, it is considered that this is a satisfactory result for our scene to screen matching criteria. 29.6 Previewing the Soft Proof Proofing can be carried out on screen using the soft proof feature which is described in detail below. However, before proceeding further it is worth emphasising that the purpose of Photoshop is to prepare images for both desktop printers and for a large number of different press printers of various types. Thus, in order to provide an indication of how the print will appear for these various final destinations, Photoshop provides the facility to switch the display from the ‘normal’ mode to the ‘soft proof’ mode. In doing so the dual reversible facility of ICC profiles described in Sections 27.3 and 27.4 is utilised to emulate the proof rendition, that is, the profile provides not only the parameters for transforming the working space image to the print space, but also provides the parameters for the complementary process of converting the print colour space image back to the working colour space. Thus one is provided with the
540 Colour Reproduction in Electronic Imaging Systems option of displaying either the normal image directly from the working space or selecting for comparison, an image based upon the values in the print colour space; that is, a soft proof of what can be expected from a print. Before proceeding into the complexities of printing with Photoshop, it may help to clarify the situation by reviewing once more the appropriate elements of the workflow diagram, as illustrated in Figure 29.32. Camera RAW File Photo DNG storage viewer JPEG & TIFF i/p i/p o/p Working space Monitor Set to a working a. De-mosaicing colour space o/p Proof setup Soft proof Transform b. Colour balance of choice. to monitor c. Standard wide Transform General image to working colour chromaticty manipulation and file colour space space gamut type conversion as d. Image reequired for output, Transform Local adjustments RGB or CMYK, etc. to proof printer e. Output colour gamut colour space Hard proof o/p i/p Transform to printer colour space Camera raw Photoshop Photoshop output processing image processing processing © RKD 2004/8 Computer Figure 29.32 The simplified proof switching arrangements in Photoshop. The complexity in the switching arrangements associated with printing is related to the ability to both view a soft proof and print a hard proof of how the image would appear on a commercial printing press. The switch positions shown relate to the ‘normal’ viewing and desktop printing positions. The support of proofing enables an appropriate press profile to be utilised in both the reverse and forward directions to enable the appearance of the press print to be emulated individually on both the monitor and the desktop printer. Setting up the proofing feature is achieved by selecting the menu item ‘View/Proof Setup’ causing the screenshot illustrated in Figure 29.33 to be displayed. The resulting list enables the selection of the printer colour space to be used as the basis of the proof, note the choice of either ‘Custom Setup’ or ‘Working CMYK’ as the two options relevant to this task. The latter option will produce a hard proof based upon the characteristics of the printer system originally selected (see Section 29.2) as the basis for the ‘CMYK:’ colour space in the ‘Color Settings →Working Spaces →CMYK panel’ and the profile name will be added to the image title as a reminder that the proofing image is on display. If the ‘Proof Setup’ option ‘Custom Setup’ is selected the ‘Customize Proof Condition’ panel appears on the display as illustrated in Figure 29.34.
Colour Management in the Desktop Workflow 541 Figure 29.33 The proofing menus selection. Figure 29.34 The proof customise panel. Activate the ‘Device to Simulate’ option and select the alternate printing system required, in this case the ‘U.S. Web Coated (SWOP) v2’ system. Select ‘Rendering Intent’ to ‘Absolute Colorimetric’. (Interestingly this option is not provided for the ‘Working CMYK’ alternative.) The ‘Reset’ and the two ‘Default’ buttons appearing on the screenshot illustration above incorrectly reflect the actual name of these buttons which are ‘Cancel’, ‘Load’ and ‘Save’, respectively. Thus if required, the settings selected may be saved as a template for future use
542 Colour Reproduction in Electronic Imaging Systems by selecting the ‘Save’ button and nominating a name for this proof condition. Selecting the ‘OK’ button will return the display to the ‘Color Management’ box. The display may now be switched between the ‘normal’ display and the soft proof display by selecting the menu item ‘View →Proof Colors’ or more conveniently by alternately selecting the keys ‘Ctrl+Y’. Figure 29.35 Image title includes proofing profile. This control operates on the current image only and will add the name of the printer process to the title bar of the image window to remind you that you are looking at a proof display, as can be seen in the screenshot illustrated in Figure 29.35. With a good quality desktop printer and paper profile as the default, selecting the proofing option causes only relatively minor changes in display to be seen even on this testing chart, indicating that this printer’s pigments are only just limited by the scene colours. If however a commercial print process is selected as the proof press more significant changes will be seen. 29.7 Matching the Print to the Display and the Scene 29.7.1 Introduction A workflow process which produces a good match between the scene and display for in-gamut colours has been achieved. The next step is to produce a print to compare with both the display and the original ColorChecker chart. As the printer and the gamut of its inks or pigments may be incapable of containing the gamut of the display, and furthermore, there is some difficulty in matching the contrast law of the printer with that of the display, it is inevitable that this match is likely to be compromised to some degree. Nevertheless, by selecting the correct options in the workflow between the stage that achieved a good display and that required to produce a print, an optimum rendition of the image can be achieved.
Colour Management in the Desktop Workflow 543 Although inkjet printers operate in a CMYK colour space, they are driven by Photoshop with signals derived from an RGB colour space. So the printer driver will be responsible for the conversion to the appropriate CMYK working space, as described in Chapter 23. There are colour management settings options in both Photoshop and in the printer driver provided by the printer vendor. However, since both Photoshop and the printer driver offer colour management of the printer, it is important that only one of these options is activated, otherwise a correction profile will be applied twice. Epson indicates that their driver is intended for relatively simple applications, which do not have the sophistication of Photoshop. Thus in this situation colour management is best left to Photoshop and the colour management features of the printer driver should be turned off. The method of achieving this will be described below. When a printer driver is opened, it displays the range of profiles available for connecting the working space of Photoshop to the printer. For a relatively simple printer only one printer- dedicated generic profile amongst the large range available in Photoshop will be displayed, whilst the more professionally orientated printers will also include profiles for each of a range of related print papers. 29.7.2 Setting the Print Parameters of Photoshop and the Printer The Photoshop parameters associated with the printer and the printer settings are accessed via the print menu which is activated by the menu item ‘File →Print or keys, ‘Ctrl+P’ resulting in the screenshot illustrated in Figure 29.36. In legacy terms the print panel was perhaps the area which caused most confusion to the uninitiated, a confusion mostly associated with the option of using either the printer profile supplied by the printer vendor or the Photoshop printer profile. On the release of successive versions of Photoshop, Adobe has provided increasing clarity regarding these options in the print menu, supplemented by helpful comment in the ‘Descriptions’ box. In this release the most critical comment cannot be missed. Rather than risking it being overlooked, it appears with a warning triangle as the first item in the Color Management box situated on the right-hand side of the main panel. Thus if using Photoshop to manage colours, one is warned: ‘Remember to disable the printer’s colour management in the print settings dialog box’.
544 Colour Reproduction in Electronic Imaging Systems Figure 29.36 The initial print screen. 29.7.2.1 The Printer Settings In the ‘Printer Setup’ box, ensure the ‘Printer:’ selection is set to the appropriate printer. In order to abide by the warning described above, click on ‘Print Settings . . . ’ this will activate the ‘Basic’ version of the ‘Printer Properties’ panel, as illustrated in Figure 29.37. Set the parameters for the various options and click on ‘Advanced’ to display the remaining options, illustrated in Figure 29.38. Set the usual parameters as required and in the ‘Color Management’ box select the ‘ICM’ option and tick the box beneath for ‘Off (No color adjustment)’. These selections ensure that the printer driver does not apply any colour management actions to the image to be printed. Click ‘OK’ on both panels successively to return to the initial print panel.
Colour Management in the Desktop Workflow 545 Figure 29.37 Printer ‘Basic’ options. Figure 29.38 Printer ‘Advanced’ options.
546 Colour Reproduction in Electronic Imaging Systems 29.7.2.2 Photoshop Print Settings for the Local Master Print The colour management menu items of the ‘Print’ panel are illustrated in Figure 29.39. Figure 29.39 The colour management box of the ‘Print’ panel. When undertaking the following actions, note in each case the useful descriptions which appear in the ‘Description’ box. r Activate the ‘Color Handling’ options and select ‘Photoshop Manages Colors’. appro- r Activate the ‘Printer Profile’ options and select the printer and paper profile as priate. (The paper of the profile illustrated in Figure 29.34 is a matt paper with a neutral spectral reflection distribution (SRD) to match the media on which the ColorChecker r chart is produced.) ‘Absolute r Activate the unnamed printing options and select ‘Normal Printing’. r Activate the ‘Rendering Intent’ and select ‘Absolute Colorimetric’. ‘Black Point Compensation’ should be greyed out when selecting Colorimetric’.
Colour Management in the Desktop Workflow 547 At this final stage the opportunity is available to soft proof the projected rendition of the image as it will appear on the local printer. On the ‘Print’ menu (Figure 29.36), beneath the image area are three tick boxes: r Match Print Colors r Gamut Warning r Show Paper White Ticking the ‘Match Print Colors’ will cause a slight desaturation of the higher saturated chart samples on the displayed image as it emulates the printed image. Ticking the ‘Gamut Warning’ box will cause all those samples which fall outside of the printer ink gamut to appear as grey. Finally click on the ‘Print’ button to produce a normal print of the Photoshop image. 29.7.2.3 Photoshop Print Settings for the Hard Proof Subject to the colour gamut of the desktop printer fully encompassing the gamut of the commercial printer process, it may be used to produce a hard proof of the latter’s performance. Activate the ‘Photoshop Print Settings’ panel if not already displayed and set all options as described for producing the local master print as described in the previous section. In the lower half of the ‘Color Management’ box, activate the unnamed printing option area to change the setting from ‘Normal Printing’ to ‘Hard Proof’. This will change the remainder of the options in this box as illustrated in Figure 29.40. Figure 29.40 Colour management hard proof box. Activate the ‘Proof Setup’ options and note the choice of either ‘Custom Setup’ or ‘Working CMYK’. The latter option will produce a hard proof based upon the characteristics of the printer system originally selected as the ‘CMYK:’ colour space in the ‘Color Settings → Working Spaces →CMYK panel’ and the profile name will be listed beneath as the ‘Proofing Profile’.
548 Colour Reproduction in Electronic Imaging Systems If the ‘Proof Setup’ option ‘Custom Setup’ is selected the same ‘Customize Proof Condition’ panel as that previously reviewed when describing the soft proofing arrangements within the main screen of Photoshop appears on the display as illustrated in Figure 29.33. Furthermore, the procedure for selecting the hard proof custom profile is identical to that described in Section 29.6 for the soft proof. As described previously for the local printer procedure, the tick boxes under the image in the ‘Photoshop Print Settings’ panel may be ticked to see a soft proof associated with the printing press selected above. Activating the ‘Print’ button will produce a hard proof of the image as it would appear on the commercial printing press. 29.7.3 Appraising the Match of Display and Print As when appraising the match of the display and the original, there are practical reasons why it is not possible to provide a critical objective basis for assessment based upon viewing the image in a printed book. Nevertheless, even with these provisos it can be seen from the photograph of the screen and the print, illustrated in Figure 29.41, that there is a good match. As with the original capture of the scene, this image of the print and original was captured as a raw file on the same camera, the only adjustments being auto colour balance on the white sample of the original ColorChecker chart. Figure 29.41 Comparison of print and display.
Colour Management in the Desktop Workflow 549 29.7.4 Appraising the Match of the Scene with the Print The visual appraisal of the match between ColorChecker chart and the print is subjectively close to excellent and vindicates the use of colour management in ensuring a high quality of colour image reproduction. The print and the original were photographed together under weak sunlight at approxi- mately 45 degrees and printed to give some indication of the quality achieved as illustrated in Figure 29.42. Such a comparison is a very testing exercise and unfortunately the camera view was not as good as the visual comparison. Nevertheless, it does illustrate that even with this highly critical test the results were reasonably favourable. It is worthy of emphasis that the print appearing here has suffered any inaccuracies that might be present in any of the following processes: r Original camera capture r Processing through Photoshop r Printing Figure 29.42 Comparison of original image with print (lower chart).
550 Colour Reproduction in Electronic Imaging Systems r Secondary camera capture r More processing through Photoshop r Printing for the book Thus although the reader has not seen the original visual comparison, it can be envisaged that without the last three processes the result may be deemed to be very satisfactory. 29.8 Summary of Activities to Assist in Obtaining Good Colour Reproduction r If possible place a neutral greyscale in the scene. colours, in the camera use in order of r To minimise the risk of clipping out of gamut r preference, RAW, Adobe RGB or sRGB colour mode formats. do not change during r Set up display to standard conditions. r Provide a matching standard print viewing environment. Select Kodak ProPhotoRGB for the RAW viewer and Photoshop; r processing. the image on a neutral greyscale, standard grey card or a true white in the Colour balance r scene. the image to a DNG format file. Photoshop; ensure printer driver colour r For archive, save of printer colour management by Select the option r management is turned off. printer manufacturer. chart r If in any doubt about performance use inks specified by a match to the ColorChecker Select a satisfactory print paper colour of neutral hue if is required.
30 Colour Management by Profile Maintenance 30.1 The Requirement to Incorporate New Profiles There are occasions when it becomes necessary to incorporate new profiles into the pho- tographic workflow, either because the original no longer reflects the characteristics of the equipment it was designed to complement or because a new item has been added to the work- flow without an accompanying profile. Sometimes the vendor develops an improved profile for their product. In the normal course of events the profiles supplied by equipment vendors adequately reflect the performance of the elements in the workflow they are intended to complement, from the camera to the print media, and by adopting the procedures described in the last two chapters, satisfactory colour reproduction is usually achieved. However, experience indicates that there can come a time when no matter how conscientiously colour management is practised the rendered image compares poorly with the original. This is usually a sign that somewhere in the workflow one of the items of equipment is no longer performing in the manner which dictated the parameter values incorporated in the associated profile, and in consequence some sort of remedial action is required. The cause of the change in operating characteristics may be either due to instability of performance or, more seriously, an equipment fault. In the latter case either the equipment must be repaired or a decision is made to replace it. However, very often the problem is one of instability caused either by changes within the equipment or in its set-up; assuming the set-up has been checked, then it is reasonable to assume that for one reason or another operating characteristics have changed. In these circumstances the solution is to replace the profile with one matched to the new characteristics. The items which most frequently require attention are the monitor, the printer and the projector; the scanner is a relatively stable item although it can sometimes benefit from being re-profiled. Occasionally a new item is added to the workflow without the benefit of an accompanying profile; most frequently a new brand of paper for the printer. Since a printer profile is based upon the joint characteristics of the printer and the paper, it is impractical for the vendor of the paper to provide a matching profile for the paper alone. Many paper vendors provide a profile Colour Reproduction in Electronic Imaging Systems: Photography, Television, Cinematography, First Edition. Michael S Tooms. © 2016 John Wiley & Sons, Ltd. Published 2016 by John Wiley & Sons, Ltd. Companion Website: www.wiley.com/go/toomscolour
552 Colour Reproduction in Electronic Imaging Systems service whereby they provide a file containing a test set of colour samples from which the user provides a print on the new paper, which is then sent to the vendor who measures the resultant colours and responds with a new profile which is loaded into the computer profile library. It is usually a relatively straightforward matter to determine which profiles need attention. If after the set-up procedures described in Section 28.3 have been implemented there is a poor match between the original image and the monitor display, then it is likely that the monitor profile should be replaced. However, if there is a good match between the original image and the rendered image on the monitor but a poor match to the printed image, then it is likely that the printer profile requires to be replaced. The remainder of this chapter provides a brief description of the procedure for generating new profiles, whether that is by the vendor or the user. 30.2 Preparing to Generate a Profile The theoretical aspects of generating a profile have been covered in earlier chapters (Sec- tions 12.2, 23.4, 27.3 and 27.4.) where fundamentally two types of profiles were identified. A simple matrix-based profile is used when the characteristics of the device are precisely defined and stable, and table-based profiles are used when only an imprecise description of the characteristics is known and/or the characteristics are not stable. In the latter case, there may be a need to generate a new profile each time the characteristics change. For table-based profiles it will be recalled a learning process is required, whereby a set of specified colour samples is used to generate an output from the device and the results are used to build a table which relates the output to the input colours for the profile. It is the latter approach which is usually appropriate to the devices requiring re-profiling; this also includes the new printer paper-printer combination profile. 30.2.1 Items Required in Generating a Profile From the above description it is evident that in order to generate a profile the following items will be required: r A file containing colour samples of known RGB values r A spectrophotometer for measuring the colour samples at the output of the device r A calculator to calculate the required table values from the measured sample values r A software application for generating the profile Taken in isolation the list implies a technically demanding procedure; however, technology has now progressed to the point where the profile software application incorporates all but the spectrophotometer itself. Nevertheless the application does control the spectrophotometer via an interface to the workflow computer in order that the measurements made are captured directly by the application. A number of vendors supply this type of software application package in kit form with the software guiding the user through a number of steps culminating in the generation of the profile. In the following, as an example of the procedure, the processes available using the X-Rite ‘i1 Photo Pro 2’ kit will be briefly described.
Colour Management by Profile Maintenance 553 30.3 Generating Profiles 30.3.1 The Home Screen Activating the i1 Profiler causes the ‘Home’ screen to be displayed as illustrated in Figure 30.1. Figure 30.1 The i1Profiler ‘Home’ display. On the left of the screen the various profile operations are displayed together with the options available. At the bottom right is the option to display the list of training videos which run through each of the activities associated with producing a profile for each of the items on the left of the screen. As an example of creating a profile the ‘Display Profiling’ operation will be described. 30.3.2 Display Profiling Selecting the Display ▶ Profiling option will cause the Display Settings screen to appear as illustrated in Figure 30.2. At the bottom of the screen are shown the five stages in producing the profile, with the centre part of the screen providing the options to set the required display settings. The active stage may be selected via either the ▶ Next icon or the appropriate icon along the bottom of the display.
554 Colour Reproduction in Electronic Imaging Systems Figure 30.2 Display profile, display settings. 30.3.2.1 Display Settings The Display Settings offers the option of selecting parameter values from those shown in Table 30.1: Table 30.1 Display settings Parameter Display setting White point D50, D55, D65, D75 Luminance 80, 100, 120, 160 (ISO 3664 condition P2), 250 nits Contrast ratio Native, Custom 10 – 1000, ICC PCS Black point (287:1), Flare correct from printer profile Ambient light smart control Measure and adjust for flare Adjust profile based on my ambient light As can be seen a wide range of settings is available, comprehensively covering a range of normal operations; it is interesting to note that the ISO and ICC recommended settings detailed in Sections 26.3 and 27.3 respectively for highlight luminance and black point are offered as a default.
Colour Management by Profile Maintenance 555 30.3.2.2 Profile Settings The Profile Settings offer the options listed in Table 30.2 Table 30.2 Profile settings Parameter Profile settings Chromatic adaptation Bradford (default), CIECAT02, Sharp, CMCCAT2000 ICC profile version Version 2, Version 4 (Default) Tone response curve Standard (Default), sRGB Gamma Variable to 2 decimal places from 1.00 to 3.00 Profile type Table based, matrix based (Default) The chromatic adaptation transforms are those described in Section 5.2. Care needs to be taken in selecting the ICC Profile Version; Version 4 (Default) would appear the obvious choice; however, as indicated in Section 27.4, since V4 is not compatible with a number of applications many workers continue to use V2. The tone response curve options are associated with the Gamma settings; if the sRGB tone response (detailed in Section 24.2) is selected the Gamma options are greyed out. Selecting Standard (Default) activates the Gamma selection slider which would normally be set to 2.2. 30.3.2.3 Patch Set Three patch sets are offered: small – 118 samples, medium – 211 samples and large – 462 sam- ples. Selecting the larger patch set will provide more samples for the software to make increasingly more accurate profiles but will also make the measurement process longer, up to 25 minutes for the large patch set. If required, patches may also be selected from both the Pantone range, subject to the Pantone Color Manager application being available, and from a JPEG image selectable from the computer folders. In the latter case the software will select up to 20 sample colours from the image and add them to the patch set selected. The various combinations of patch sets may be viewed by selecting the appropriate icon at the top left of the viewing area. 30.3.2.4 Measurement On selecting the Measurement screen, the patch set is displayed centrally and on the left of the screen two action options are provided. If not already done, the software reminds the user to connect the spectrophotometer to the computer. The first action option is to calibrate the spectrophotometer which is undertaken by placing it on the calibration frame, which incorporates a small white calibration tile, and clicking the calibration button on the display or on the spectrophotometer. The second action is to inform the software whether the monitor will be adjusted via ‘Automatic Display Control (ADC)’ or manually by the user. ADC is a software adjustment facility incorporated into many current monitors and enables the i1Profile software to manage the monitor adjustments. Once all the options have been selected the ‘Start Measurement’ button is activated and the user is guided to set the spectrophotometer against the face of the screen with the aid of
556 Colour Reproduction in Electronic Imaging Systems the carrier frame provided. Once the software detects the properly located spectrophotometer, it takes control of the screen and commences to display in sequence in full screen mode the patches previously selected. As indicated above this sequence can take up to 25 minutes to complete. 30.3.2.5 ICC Profile Once the measurements are complete, the ICC Profile icon is selected and the user is invited to provide a name for the new profile. Once named, the new profile is stored in the appropriate folder and also automatically made the new default profile for the monitor. 30.3.3 Other Profiling The other profiling procedures follow a very similar pattern. Where there are significant differences they are broadly described in the following paragraphs. 30.3.3.1 Printer Profiling The workflow for producing a printer profile commences with the selection of a suitable patch set, generally the printer patch sets contain more patches than those used for monitor profiling to assist in ensuring a satisfactory level of accuracy from the printer. An additional stage is included in the workflow to format the patches into a suitable test chart in readiness for printing. Figure 30.3 illustrates a print of half the samples from an 800 sample selection. A measurement reading tray is provided to accommodate the resulting print which enables the spectrophotometer to be mounted on a sliding frame above. The user then slowly slides the Figure 30.3 Illustration of half the samples from an 800 sample selection print.
Colour Management by Profile Maintenance 557 spectrophotometer across each row of printed patches in turn enabling the software to measure the colour of each patch. A number of profile parameter values are then set before the profile is created. 30.3.3.2 Scanner Profiling A recognisable test card is inserted into the scanner, the ColorChecker chart being acceptable. All colour management settings on the scanner should be set to off and a TIFF file (Section 25.3) format selected for recording the file. The contents of the file are then measured and an appropriate profile is added to the file. This profile is then stored in the computer profile folder. When a file from the scanner is opened in Photoshop, as described in Section 29.5, either the native profile should be replaced with the new profile or, where no native profile exists, the new profile should be assigned to the image file.
Part 5C Colour Reproduction in Digital Cinematography Introduction Cinematography was the last of the reproduction media to commence the adoption of digital technology in place of film during the 1990s/2000s. There were good reasons for this apparent delay; although colour television services had matured for some 50 years, and during that time the quality of reproduction had improved dramatically, nevertheless, when it came to producing motion pictures on large cinema screens with considerably wider angles of view compared to even large screen domestic television, the results compared poorly with what could be achieved by film. The principal limitation was the comparatively poor resolution of television, even the current high definition television system was deemed barely adequate for the larger cinema screen. Nevertheless, in system technology terms, television, being based on the reproduction of finite sequences of activity, as opposed to digital still photography, is the clear forerunner for digital cinema. Furthermore, unlike photography, which has to service a very extensive range of users each with the freedom to adopt system parameters from a wide range of options, the cinematographic industry had the opportunity to define a single set of worldwide standards. Digital cinema was conceived in an era when international standards in other media were already well established and potentially had a clear stage to set ideal specifications from conception, without the limitations of accommodating legacy electronic practices. Colour Reproduction in Electronic Imaging Systems: Photography, Television, Cinematography, First Edition. Michael S Tooms. © 2016 John Wiley & Sons, Ltd. Published 2016 by John Wiley & Sons, Ltd. Companion Website: www.wiley.com/go/toomscolour
560 Colour Reproduction in Electronic Imaging Systems The early serious experiments towards the end of the twentieth century commenced by introducing digital electronics into the post-production (often abbreviated to ‘post’) processes of some post houses, whilst a few enthusiastic producers went on to use the advanced television cameras of the day to produce digital image tapes. In the wide range of procedures comprising the post workflow these digital images were easier to manipulate and the use of tape based rather than film based clips significantly enhanced the efficiency of the operation. Once post was complete the tape was converted to film for distribution to cinemas; thus establishing a digital workflow pattern to a section of the overall workflow which gave direction to the evolvement of the digital cinema standards. The following chapters provide a broad outline of the digital cinematographic workflow and a description of how in the 2000s the major production and distribution houses came together to specify the digital cinematography standards for each of the two major workflows: production and post, and distribution and exhibition. Author’s Note. In January of 2015 just as the final chapter of this book was nearing completion, a major review and re-issue of the standards documentation undertaken by the body responsible for deriving these production and post standards became available, providing the author with the incentive to add a further chapter (34) in which the supplementary elements of the specifications are described and in which the status of the industry in the 2010s, in the light of the level of adoption of these industry standards, is reviewed. Acronyms Table 31.0 List of acronyms used in the digital cinema image specifications ACRONYM Definition ACES Academy Color Encoding Specification ADX Academy Density Exchange Encoding AMPAS Academy of Motion Picture Arts and Sciences Academy Academy of Motion Picture Arts and Sciences APD Academy Printing Density ASC American Society of Cinematographers CDL Colour Decision List CMF Colour Matching Function DCDM Digital Cinema Distribution Master DCI Digital Cinema Initiatives DCP Digital Cinema Package DLP Digital Light Processing DMPC Digital Motion Picture Cameras DSM Digital Source Master EDL Edit Decision List IDT Input Device Transform OCES Output Colour Encoded Space PCS Profile Connection Space ODT Output Device Transform RDD Reference Display Device RICD Reference Input Capture Device RRT Reference Rendering Transform SMPTE Society of Motion Picture and Television Engineers
Colour Reproduction in Digital Cinematography 561 Acronyms used in the workplace have been adopted throughout this book, always defined at the first occurrence in a chapter, which is deemed usually sufficient to carry the reader through without reference to a list of acronyms used. However, the specifications associated with the digitisation of the film industry have far more than the usual preponderance of acronyms, particularly those associated with production; and more than many readers will remember when reading through a chapter. Thus although the usual practice of defining the first occurrence will continue, a list of acronyms is also provided below for easy reference whilst reading. Reference to the system configuration diagram in Figure 32.2 illustrates the functions which relate to many of the acronyms appearing in Table 31.0.
31 The Evolution of Digital Cinema 31.1 Background Over a period of nearly 100 years the cinematographic industry had developed a well- established, rich and extensive history based on the use of film to capture the image, to edit and manipulate the image in post-production (post), to distribute the film worldwide and to exhibit the film in tens of thousands of cinemas. Furthermore, should they have given it consideration, it would seem likely the cinema audience would have indicated they were very satisfied with the technical quality of the rendered image on screen. Why then should there have been an imperative to change such a successful industry away from film-based to digital-based operations? In order to respond to this question we first need to be aware of the workflow of the industry from scene capture to exhibition in the local cinema. Figure 31.1 provides an overview of that workflow. Scene Camera Post Master Inter- Release Distribu- Projection Cinema capture negative negative prints tion Viewing Answer theatre Print Craft workflow Distribution and exhibition workflow Figure 31.1 A broad indication of the traditional cinematographic workflow. The cinematographer is the technical craftsman or woman responsible for the appearance of the image, taking in the lighting of the scene, the camera shot and exposure, the artistic adjustments during post and the answer print, which is the culmination of the creative process. From that point on the process is objective, with care necessary to ensure that the release prints when distributed, projected and exhibited reflect the intent of the cinematographer and director as manifest in the answer print. Colour Reproduction in Electronic Imaging Systems: Photography, Television, Cinematography, First Edition. Michael S Tooms. © 2016 John Wiley & Sons, Ltd. Published 2016 by John Wiley & Sons, Ltd. Companion Website: www.wiley.com/go/toomscolour
564 Colour Reproduction in Electronic Imaging Systems From the early days of cinematography the basis of operations were such that the logistics of shooting were orientated around one camera, which implied a sequential shooting plan based upon ensuring that irrespective of the time sequence of the plot, all scenes related to a particular location or set were shot before moving on to the next location, which in a major production were possibly weeks or months apart. Such a practice implied the support of a comparatively sophisticated logistical capture and post-production operation, complete with various intermediate film processes to address the negative-to-positive film transfers, special effects, editing, dubbing and colour grading. Once the film master was available, a large number of release prints were required to service each cinema circuit which in turn were distributed around the world, an intensive logistic and expensive exercise. As early as the 1950s, enthusiastic cinematographic craftsmen with some experience in television production techniques saw the potential for introducing these techniques into the film world, where the much simpler logistics of shooting and flexibility in post-production could save on the costs of the various film transfers and grading sequences required, and companies were established to exploit these savings. Once the television-based video tape was mastered in post it was transferred to film using a telerecording technique whereby a film camera was arranged to view a special high-definition television (HDTV) display. These early attempts were not successful. The technology of the time was incapable of providing the degree of resolution, dynamic tone range and lack of electronic noise accepted as normal in the film world. By the early 1990s, with the advances in television technology which had led to the move from analogue to digital technology, the setting of the HDTV standard and the availability of equipment to support the standard, it became practical to transfer the processed negative film to video. During that decade an increasing number of post houses offered the service of transferring the film negative-based images to tape, editing and conforming it, applying special effects and colour grading it in the video domain, before recording the master video back to film to produce the internegative for making the release prints for distribution. Towards the end of the 1990s, with the adoption of higher sensitivity and lower noise image sensors, then for particular genres of film, the time had come to start to capture images using high performance digital motion picture cameras (DMPCs) and to manipulate these images directly in post as outlined above. Once post was complete the digital master was transferred to film for archive, distribution and exhibition. Thus for a number of years the industry supported two parallel paths for those elements of the workflow from image capture to the production of a master, one based upon the range of traditional film techniques and the other increasingly based upon digital techniques. As the number of productions adopting digital techniques proliferated so too did the number of colour space specifications used for scene capture, leading to confusion and often poor results when it became necessary to use different post houses for different aspects of post- production. Furthermore, there was a widespread concern in the industry relating to the poor match between the accepted ‘film look’ of several decades and the look of the digital material, which often manifested itself as a strong resistance to adopting digital methods of production. These concerns led to the various representative organisations of the craftsmen, engi- neers, technicians and operators in the industry to appoint committees to review the situation with the aim of establishing projects to evolve the technical specifications to cover every aspect of the digital workflow from lighting the scene to exhibiting in the cinema. In considering the extent of this project, the work-flow naturally split into two clearly iden- tifiable sets of activities, the production and the cinema operations. The production operation
The Evolution of Digital Cinema 565 comprises scene capture, post, and the rendering of the master; and the cinema operation comprises the production of the release prints, their distribution, the cinema environment and projection. In 2004, under the auspices of The Science and Technology Council of the Academy of Motion Picture Arts and Sciences (the Academy or AMPAS) some 50 leading technologists and practitioners, with contributions from the American Society of Cinematog- raphers (ASC), addressed the role for generating a specification for the former; and the major studios came together in 2002 to form the digital cinema initiatives (DCI) group to address the latter. The DCI relied upon the society of motion picture and television engineers (SMPTE) to establish a technology committee to specify the image aspects of the specification for the cinema operation. These three organisations called upon experts from across the film and tele- vision industries to form the various committees which undertook this very considerable range of tasks. The SMPTE also took on the responsibility for transforming the resulting Academy specification into an international standard. Although these groups responsible for the two main elements of the workflow worked independently of each other, each was aware of the interface point in the workflow between them and for the sake of technical coherence we will consider the work of the two groups as a single project; a project with the objective to take the mixed operations of film and digital to a fully digital workflow from scene capture to exhibition, with options to ingest film-derived material at appropriate points in the workflow. 31.2 Workflow at Project Commencement The mixed workflows which had evolved at the time of project commencement can be repre- sented by the paths illustrated in Figure 31.2. The workflows for which each organisation was responsible are indicated by the shaded backgrounds of the diagram. It was recognised that the traditional film workflow indicated in the top line of the Academy workflow would continue for several years, albeit with slowly diminishing relevance. Film Film Negative capture post master Scene Film Scan Digital Digital Inter- Release Distribu- Projection Cinema capture film post master negative prints tion Digital Digital Digital capture post master Academy Digital cinema intitative (DCI) Figure 31.2 A representation of the principal workflows at project inception.
566 Colour Reproduction in Electronic Imaging Systems The intermediate line of the Academy workflow represented the growing number of post houses capable of transferring the image of the scene captured on film to a digital format, where the ongoing post operations can be handled more flexibly, accurately and cost-effectively. The resulting digital master is transferred to film for initiating the traditional release prints and distribution process. The bottom line of the Academy workflow illustrates the path taken by those relatively few cinematographers at that time who had already embraced digital capture techniques, enabling the captured material to be used directly in the digital post operation. The workflow path for which the DCI would be responsible, that is the release prints, distribution, the cinema and the projector is illustrated on the right of the diagram, which with very few exceptions, was still based upon traditional film methods. 31.3 Common Goals of the Specifications There was an understanding from commencement of the project that film-based operations had achieved a high standard of technical excellence and a strong belief that it should not be compromised in any manner by the specifications to be evolved; on the contrary it was considered that as a result of what had been learned through the evolving specifications for television and photography there was now an enhanced appreciation of the parameters and their associated values which could contribute to the fidelity of reproduction, such that parameters could be specified which would ensure that future advances in technology could be exploited within the specifications. Between image capture and display, for the first time in media reproduction systems, these specifications would be device independent. Some of the relevant project goals embraced by the specification organisations were: r A colour gamut embracing all colours range of the eye using 16-bit floating-point numbers r A dynamic range exceeding the dynamic r for colour encoding between the various elements of the r A resolution capability associated with 4K pixels The capability of a seamless interchange of material workflows in post Essentially, the work of the two groups was to produce a pair of compatible colour encoding system specifications which encapsulated these aims. 31.4 The Digital Cinematographic Systems Specifications The complementary system specifications produced by the two organisations are broadly defined in the following paragraphs. 31.4.1 The Academy Color Encoding System The Science and Technology Council of the Academy, through its Image Interchange Frame- work Subcommittee, defined The Academy Color Encoding System which was first released in 2008 and which is based upon: r The Academy Color Encoding Specification (ACES) – Specification S-2008-001. The latest Version 1.0.1 was released in August of 2011.
The Evolution of Digital Cinema 567 This principal specification was supplemented by a number of complementary specifications to cover interfacing within the image interchange framework: r Specification for Logarithmic Encoding of ACES Data for use within legacy Color Grading r Systems S-2013-001 ACESproxy, an Integer Log Encoding of ACES Image Data r Specification S-2008-002 Academy Density Exchange Encoding (ADX) and the Spectral Specification r Responsivities Defining Academy Printing Density (APD) the Creation and Use of Digital Draft Procedure P-2013-001 Recommended Procedures for Camera System Input Device Transforms (IDTs) With the exception of the draft procedure, these specifications were submitted to the SMPTE for processing to international standards formats, which resulted in the following SMPTE documents: r SMPTE ST 2065-1 Academy Color Encoding Specification (ACES) Device and r SMPTE ST 2065-2 APD Spectral Responsivities, Reference Measurement r Spectral Calculation Encoding APD Values r SMPTE ST 2065-3 ADX– Image Container File Layout SMPTE ST 2065-4 ACES The specifications in the SMPTE ST 2065-1 standard do not extend to cover the full range of workflow elements specified in the ACADEMY Specification S-2008-001. Furthermore, the SMPTE documents are formal standards which contain very little of a descriptive nature, thus the description of this system in Chapter 32 is based upon the ACADEMY ACES system supplemented by references corresponding to where the SMPTE document is silent. 31.4.2 The Digital Cinema System The Digital Cinema Initiatives organisation approved the Digital Cinema System Specifica- tion1 in 2005 with Version 1.2 appearing in 2012. This is a comprehensive specification which sets out to cover every aspect of the workflow from production of the distribution master, through packaging, transport, the theatre systems, projection and security. The defining of those aspects of the specification relating to reproduction, that is the image encoding characteristics, the cinema viewing environment and the projector characteristics, was a role undertaken by the SMPTE on behalf of the DCI, which evolved the following standards and recommended practice: r SMPTE Standard 428-1-2006 Digital Cinema Distribution Master Level, Chromaticity r SMPTE Standard 431-1-2006 D-Cinema Exhibition Screen Luminance r and Uniformity Practice 431-2 -2007 Reference Projector and Environment for Dis- SMPTE Recommend play of DCDM in Review Rooms and Theaters 1 http://dcimovies.com/specification/DCI_DCSS_v12_with_errata_2012-1010.pdf
568 Colour Reproduction in Electronic Imaging Systems These SMPTE standard documents contain very little descriptive material; however they are supplemented by the SMPTE Engineering Guideline 432-1-2010 which provides an excellent description of the reasoning behind the selection of the parameters and their values which appear in these standards. In addition Thomas Maier, the author of the Guideline, has published much of this material in a number of issues of the SMPTE Journal. (Maier, 2007-1), (Maier, 2007-2), (Maier, 2007-3), (Maier, 2007-4), (Maier, 2008-5) (Maier, 2008-6). Much of the description of the Digital Cinema System appearing in Chapter 33 is derived from the material appearing in these journals.
32 Colour in Cinematic Production – The Academy Color Encoding System 32.1 Introduction This chapter describes the Academy Color Encoding System specified by the Subcommittee of the Science and Technology Council of the Academy of Motion Pictures Arts and Sciences. Excerpts from the Academy Color Encoding System (ACES) specifications are used with the permission of the Academy of Motion Picture Arts and Sciences. 32.2 System Definition The first task of the Image Interchange Framework Subcommittee was to define those system elements to be covered by the specification. As indicated in the previous chapter, it was recognised that digital workflows were already established within the film industry and it would be necessary therefore to embrace these activities within the image interchange framework (IIF). Essentially, two workflow paths were identified to be covered by the specification, which effectively were the two paths already containing digital elements as broadly illustrated by the lower two paths in Figure 31.1 and which are detailed in Figure 32.1. The specification embraces all activities of the workflow from the scene to the file to be used as the input to the distribution and exhibition system, defined as the digital source master (DSM). Thus, in the words of the specification: ‘The Academy Color Encoding System (ACES) is a set of components that facilitates a wide range of motion picture workflows while eliminating the ambiguity of today’s file formats. The framework is designed to support both all-digital and hybrid film-digital motion picture workflows’. Colour Reproduction in Electronic Imaging Systems: Photography, Television, Cinematography, First Edition. Michael S Tooms. © 2016 John Wiley & Sons, Ltd. Published 2016 by John Wiley & Sons, Ltd. Companion Website: www.wiley.com/go/toomscolour
570 Colour Reproduction in Electronic Imaging Systems Film Negative Clip Calibrated Conform Colour Render Film Master Inter- camera process selection transfer grade colour recorder negative negative transform Initial EDL* transfer Digital intermediate Digital Clip Colour Render Film Master Inter- Camera selection grade colour recorder negative negative transform * Edit decision list Conform Digital Established craft workflows Figure 32.1 The workflows as originally addressed by the Academy Color Encoding System (ACES). The basic ACES components are: r Color encoding and metric specifications, file format specifications, color transformations, r and an open source reference implementation. and recorders of r A set of reference images and calibration targets for film scanners for key components r Documentation on the architecture and software tools This toolkit is intended to serve as a distribution mechanism the framework including the reference implementation transforms, reference images, and documentation. Some of the original ACES documents have now been adopted by the Society of Motion Picture and Television Engineers (SMPTE) as SMPTE Standards and others are available as Academy Technical Bulletins.1 In essence, the philosophy adopted for the system configuration of the IIF builds upon the same philosophy adopted for colour management in photography, as described in Section 27.3; that is, at the centre of the configuration is a universal colour space which embraces all colours and the full spatial dynamic contrast ratio of the eye (see Section 13.3.3) and transforms the output to an agreed set of reference viewing conditions. This approach supports the coupling of the input and output devices to the IIF via interfaces with a suitable transform characteristic between the ACES colour space and the colour space of the connected device. The main difference between the photographic approach and the ACES approach is that the ACES colour space becomes the post-working colour space to be used throughout the entire image creation workflow, whereas in the photographic workflow, the profile connection space (PCS) acts merely as an interface to the core of the configuration, whilst Photoshop, for example, provides a separate colour space as the working colour space. 1 https://github.com/ampas/aces-dev/tree/v1.0/documents /ZIP
ADX Original Film Film APD film Academy density scene camera negative negative exchange encoding ADX ACE to to ACES ADX ADX to ACES/ACES to A transforms Original Reference ACES scene input capture Academy color device encoding specification IDT Original Real digital Input scene camera device transform Figure 32.2 The IIF workflow (from the ACES PowerPoint presentation).2 2 http://www.oscars.org/sites/default/files/acesoverview.pdf
Calibrated Film Film Film Theatre film recorder negative print projector reproduction ES RDT X Reference device SMPTE Theatre ADX reproduction transform Reference RRT projector Reference rendering ODT trnsform Output device Video monitor transform
572 Colour Reproduction in Electronic Imaging Systems The resulting IIF configuration is illustrated in Figure 32.2: the workflow based upon film capture is shown at the top of the diagram, the reference capture device, that is, the ideal capture device, is shown on the central workflow and the real all-digital approach is shown in the lower workflow. The interfaces between the film capture elements and the ACES, and between the ACES and the film distribution elements are dependent upon the Academy Density Exchange Encoding (ADX) as specified in S-2008-002. The remainder of this chapter describes the digital workflows in the central and lower lines of the diagram as defined in the ACES Specification S-2008-001, Version 1.0.1, August 2011. 32.3 The ACES Colour Space In defining the ACES colour space, the objective of the specification was that the space should embrace all colours at all relative luminance levels within the spatial dynamic contrast range of the eye. 32.3.1 Chromaticity Gamut In order to capture all colours, the ACES chromaticity gamut must entirely embrace the CIE 1931 spectrum locus on the chromaticity diagram. The criterion for establishing the ACES chromaticity gamut is based on using the x,y chromaticity diagram to construct the gamut and would appear to be very simply but sensibly evolved from setting the following conditions: 1. Set the red-to-green straight line section of the spectrum locus as the major element of one side of the colour space triangle. 2. Set the green primary where the line defined in (1) projects to intersect with the y-axis 3. Set the red primary on the line defined in (1) at the red end of the spectrum locus. 4. Extend a line from the red primary along the line joining the two ends of the spectrum locus. 5. Set the blue primary where the line defined in (4) intersects the y-axis. Applying these criteria results in the chromaticity gamut illustrated in the CIE x,y chro- maticity diagram in Figure 32.3a. (In Figure 32.3b the same gamut is portrayed in the CIE u′,v′ chromaticity diagram). The chromaticity coordinates of the ACES colour primaries resulting from this construction are shown in Table 32.1. Table 32.1 Chromaticity coordinates of the ACES colour space ACES x y z u′ v′ Red 0.7347 0.2653 0.0000 0.6234 0.5065 Green 0.0000 1.0000 0.0000 0.0000 0.6000 Blue 0.0001 −0.0770 1.0769 0.0002 −0.3338 System white D60 0.3217 0.3377 0.3407 0.2008 0.4742
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