INTRODUCTION TO DESKTOP COLOUR MANAGEMENT IMPROVE MONITOR, SCANNER AND PRINTER COLOUR MATCHING

Transcription

1 Colour Management Guidance Document do as we say tell me more INTRODUCTION TO DESKTOP COLOUR MANAGEMENT IMPROVE MONITOR, SCANNER AND PRINTER COLOUR MATCHING CCGM-v02 November 2002

2 INTRODUCTION Advantages of Colour Management MONITOR PROOF PRINT Monitor, Proof and/or Print can match, giving you the colour control to get it right first time. Images can be optimised for either your inkjet, press or to simulate a given print process on your proof printer, with a perfect match to monitor. Improved matching from original scan (or digital image) to output reduces colour correction time. Embedding the appropriate colour profile enables accurate interpretation of colour throughout the ongoing process. More than half the issues with colour can be resolved by correct use of the colour control options in your computer s operating system and applications. This documents gives introductory guidance for the implementation of colour management.where preferred and for larger projects, world coverage on-site consultancy is also available:

3 BEFORE YOU START This document is produced by TypeMaker Limited to increase awareness of what can be achieved from the colour management abilities of your computers operating system and applications. This includes guidance on the implementation and use of ICC profiles. Before you start to ensure you have the latest version and to download or be notified of FREE document updates click: You may be prompted by Adobe Acrobat to locate your Web browser. This document release CCGM-v02, includes: Macintosh OS9, OS X, ColorSync v3 and 4.1, Adobe Elements, Photoshop v6/7, Illustrator v9/10, Quark Xpress v4. On-line updates include more recent applications and versions: Please register on-line for notification of future updates. TypeMaker Limited ALL TRADEMARKS ARE THE PROPERTY OF THEIR RESPECTIVE OWNERS

4 HOW TO USE THIS DOCUMENT The following pages will take you though the basics. In-depth explanations can be accessed from the appendix by clicking wherever you see Please use the buttons, or the Adobe Acrobat Go to Previous View button to resume your reading place. Bookmarks are also included to aid navigation. For improved image display, click where you see this zoom icon. Then, to return to full screen view, use Go to Previous View. For detailed on-line product information www.

5 CONTENTS Contents BEFORE YOU START Introduction Advantages of colour management The problem Cause and Solution Principles of Colour management Converting with ICC profiles Colour Engines and Colour Management Models Rendering Intents and White Point www. STEP 1 Over half the way there System Optimisation and Profile Selection Setting the system colour defaults Monitor Profiling Benchmark your colour The Repro Pack Colour Settings Popular graphics applications and print driver colour options STEP 2 Device Specific Profiles Device specific profiles Scanner and Printer Profiling Remote Profiles and Profile building applications Appendix 1 Tell me more, explanations Appendix 2 Up-to-date on-line product details

6 INTRODUCTION Cause of the problem Why colours don t match Which red is RED? Paint samples A and B are both from the same brand of red paint. The slight difference in colour is due to the production process. Paint C, a different brand, is also called red but is a slightly stronger colour. It should be possible to dilute the stronger colour C to to match A, but not possible to match C using the weaker colour A. The amount of paint applied is dependent on the brush. As a brush loses bristles, the less paint it can hold and apply in a single stroke. Absorbency of the paper will also affect the final colour. Colour in a monitor, scanner, camera or printer is similar. The RGB (red, green, blue) light signals of a monitor, or sensors in a scanner/camera and the CMYK (cyan, magenta, yellow, black) inks applied by a digital or conventional press all vary in colour, between manufacturer, model and device. Like paint, the colour strength from one device can not always be matched to another and aging produces continual colour changes. RGB AND CMYK ARE DEVICE DEPENDENT COLOUR MODELS

7 INTRODUCTION Solution to the problem Describing a Colour RGB and CMYK, the main forms of colour reproduction, are device dependent colour models.to accurately describe colour, independent of a specific device, a device independent colour model is required. The Lab colour-space is a device independent theoretical colour space, based on the gamut (range) of colour which can be distinguished by the human eye. As illustrated, the colour gamut of an average monitor is smaller than Lab and printers have an even smaller gamut. Lab values are not quantities of pigment or light so colour can not be visually reproduced in it. Lab, Human Eye RGB, Monitor CMYK, Pigment Lab accurately describes colour, independent of any input or output device. ICC Colour Management is based on colour tables that translate the colour abilities of any device into Lab values.this is in the form of ICC profiles, which with a colour engine, allows for colour accurate colour transformations between device dependent colour-spaces. So, not only can you define and communicate a specific colour, but ICC profiles give the ability to reproduce that colour on other devices.

8 INTRODUCTION Solution to the problem Making colours match Colour control with ICC profiles An ICC profile describes how a specific RGB or CMYK device will capture, display or print colour. Profiles can contain both input and output tables, this enables transformations from RGB or CMYK into and out of the Lab colour-space. The Colour Engine, ColorSync on the Macintosh (ICM2 in Windows), enables colour transformations between profiles. The majority of graphics applications are now ICC aware and can be configured to use ICC profiles for display and conversion between colour-spaces. A range of profile building applications are available, covering a wide price range and abilities. Many devices include generic profiles, supplied with the device or from the manufacturer s web-site.these are better than nothing, but should only be treated as a stepping stone to building device specific profiles. Every device is different and changes with age. Environment, print drivers and papers can further invalidate a generic profile. The ICC and Profiles:

9 INTRODUCTION Principles of Colour Management Profiles Assign or Convert? Assigning a profile to an image, will NOT change the image values (RGB or CMYK separation data), but defines how the colour values of the image should be interpreted.this only alters the colour appearance (interpretation) of the image. Converting between two profiles will change the image values, generally to achieve one of the following: 1)To optimise the colour appearance of the image when viewed (or printed) based on the new profile (RGB to CMYK conversion). 2)To achieve accurate colour matching between print processes. Ideally this results in identical colour appearance through different colour values (CMYK to CMYK conversion). Same separation values different colours Different separation values matching colours

10 INTRODUCTION Profile Transformations An ICC profile transformation is not only applied when an image is converted from RGB to CMYK or CMYK to CMYK. Profiles are also used On the Fly for displaying an image on a monitor. Without this ability we would have to work within our monitors RGB values and colour-space. Lab R G B ORIGINAL VALUES R G B MONITOR DISPLAY VALUES Lab C M Y K ORIGINAL VALUES R G B MONITOR DISPLAY VALUES Profile Transformations:

11 CONVERTING IMAGES WITH ICC PROFILES Converting images with ICC Profiles Colour Management Models To convert an image using ICC profiles a colour conversion engine is required.this is known as ColorSync in the Macintosh operating system (ICM2 in Windows). Various vendors supply their own interpretation of how such transformations should be applied, in the form of CMM s (Colour Management Models).Your preferred CMM is set in the ColorSync control panel. Changing this choice can produce subtle colour differences. However, the Adobe Colour Engine (ACE), can only be selected from and used within Adobe applications. Even if a particular CMM is selected for use when converting images locally on the workstation, if profile conversions are also applied on the fly, for example in the RIP of a proof printer, the CMM licensed by the RIP manufacturer will be used. A choice of four rendering intents determine the nature of an image s change in colour during a conversion from a source to a destination profile.

12 CONVERTING IMAGES WITH ICC PROFILES Rendering Intents It is important to use the most appropriate rendering intent for each task as required: Perceptual When converting an image from a large to a small colour-space, such as an RGB scanner profile to a CMYK print profile. Relative Colorimetric Most appropriately used when converting into a profile of a larger (or equivalent) gamut, such as to simulate the colour fidelity of a CMYK press profile to a proofer profile, where variation between the profile s paper colours are ignored. Saturation Stretches/squashes the source gamut into the destination gamut producing the most vibrant colour range achievable, but distorting the relationship of colours. More appropriate for graphic illustrations than photographic images. Absolute Colorimetric Same as Relative Colorimetric;however, variations between the profile s paper colours are compensated for.this results in a printed overall paper colour simulation. Rendering Intents:

13 STEP ONE These three points can resolve over half your colour management issues: Operating System colour settings Correct and verified monitor profile Application colour settings Indicates For improved image legibility, click to zoom

14 SYSTEM OPTIMISATION & PROFILE SELECTION Workstation Optimisation Your Macintosh computer s operating system includes ColorSync, this being Apple s colour framework.windows uses its own colour management system. Before configuring your colour management, ensure that a current version of ColorSync, appropriate for the OS that you are running, is installed. Details of current recommended OS/ColorSync combinations, are available at: Colour Management System Options Your default profiles, device profiles and CMMs can be set within your operating system controls. Although you may later find that such choices are being made directly in applications such as Adobe Photoshop, it is still good procedure to set appropriate defaults. As a minimum, if you are running a Mac OS, check the correct version of ColorSync is installed. Click the appropriate OS link below for more information:

15 MONITOR PROFILING The Monitor Profile The monitor profile is selected in the colour tab of the monitor control panel or the displays preference pane. This tells the computer how to adjust document colours for a correct monitor display. Before selecting calibrate to build a new profile, the following pages cover monitor settings and the profiling options available. Monitor profiling applications generally set a newly built profile automatically here. The selected profile name is then also displayed in the ColorSync control panel under OS 9 but can only be changed in this, the monitor control panel.with OS X you can use the ColorSync Utility to change the display profile.

16 MONITOR PROFILING Monitor set-up In the monitor tab of the monitor control panel or the display tab of the display preference pane check that the desired Colors and Resolution are selected. There are a number of options available to build a monitor profile.as a general rule, the more steps involved the better the profile and the use of a measuring instrument can greatly improve quality. Setting the monitor s hardware white point is the best starting point.

17 MONITOR PROFILING Profile your Monitor The majority of users will already have the following options A and B available to them for defining a monitor profile. A) Apple Monitor Calibration Assistant is included as part of the Macintosh Operating System (OS8 and above). B) Adobe Gamma Step by Step (Assistant) is installed in your Control Panel during installation of Adobe Photoshop 6 but is not included with Photoshop 7 and does not run under OS X. C) Instrument based calibration and profiling requires a small investment but one that should be easily justifiable. Before you build a new monitor profile, check what is currently being used (in the monitor control panel), as this may have been specially built for your monitor.the Repro Pack as described on the following pages will help benchmark your current level of accuracy. For additional guidance on the above methods of monitor profiling: An accurate monitor is the key to confidence in your colour management. www.

18 BENCHMARK YOUR COLOUR Verify your monitor The Repro Pack Regardless of whether you have profiled a 5 year old consumer level monitor or are using anything up to a Barco Reference Calibrator V monitor, your viewed image will not be correct if the application displaying the image is not configured correctly. This, combined with using an incorrect monitor profile, is the cause of over half of colour related problems and can all be solved for little or no additional investment. Configuring applications, such as Adobe Photoshop, is covered in the following section and is crucial to being able to verify that your monitor profile is correct and that ongoing work is being similarly displayed correctly. Ideally a digital test image, embedded profile and reference print are required to verify the accuracy of the monitor profile, viewing conditions and application set-up.

19 BENCHMARK YOUR COLOUR The ColourConfidence Repro Pack covers these requirements and also includes a RHEM strip for verification of appropriate lighting conditions. The Repro Pack can also be used for evaluation and validation of proofing devices and is the ideal first step to visually quantifying and benchmarking the accuracy of your colour. RHEM Lighting Indicator Strips and importance of viewing conditions www. Repro Pack www. D50 / 5,000K Viewing Booths www.

20 APPLICATION COLOUR SETTINGS Colour configuration of graphics applications Configuration of colour management in applications such as Adobe Photoshop with the correct use of options available, is crucial to the successful implementation of Colour Management. Explanations of setting up and using colour management in the main graphics applications are included later in this document. Ideally a simple viewing application that will display an image correctly, clearly identifying the image reference profile, will help verify colour settings in the more complex applications. Such an image viewer (Preview) is included with Mac OSX but not as part of OS9.

21 APPLICATION COLOUR SETTINGS Currently, colour guidance settings for the following applications are included and the appropriate pages of the appendix can be accessed from here. If you have not already, please register FREE for updates covering future application/version colour guidance at: Adobe Photoshop Elements Adobe Photoshop v6/7 Adobe Illustrator v9/10 Quark Xpress v4.1

22 PRINT DRIVER COLOUR OPTIONS Print Driver colour related options Options available in your print dialogue will vary on the active print driver, device and application. Application specific options, as described previously for the appropriate applications, is the suggested method to apply proofer related colour management when printing to a RIP which does not have its own ICC colour management options. Based on this, the OS 9 print driver colour options Colour Matching, should be left on the default of Color/Grayscale, so no additional colour conversions are applied. OS X handles printer colour management differently and this option is not available. Printer Specific Options are as they say and the options available will vary on the selected output device. Some may include colour related options such as pint/paper quality which can have a big effect on printed colour.the easiest way to verify optimum settings is to print ramps of 0 100% CMYK based on different print/paper options to determine the best for you device/paper combination. Details and test images for optimising your printer specific settings are available from: Proofer Optimisation www.

23 REVIEW STEP ONE OF STEP Over ONE half theway there Review of Step One Having followed through the Step One procedures correctly, the following assumptions can be made: RGB and CMYK images on screen are being interpreted and displayed with consistent repeatable colour. Images passed on, can similarly be interpreted with the same colour fidelity. Converting such an image into another RGB or CMYK profile will produce an optimised transformation based on the selected destination profile and rendering intent. Two limiting factors are the quality of the monitor/profile and the ability of the output print device to match the destination profile. The accuracy and validity of all this can be easily bench-marked with a Repro Pack. This can also be used as a weekly confidence check. Separations from the CMYK PressMatch profile, included with the Repro Pack, may also improve image colour quality on press. Repro Pack: www.

24 REVIEW OF STEP ONE If not already used, instrument based monitor profiling will help achieve maximum potential from your monitor. Instrumented monitor profiling: www. Now that you are in control of images scanned in-house, how do you efficiently integrate supplied images containing a questionable or no embedded profile? What profile?: www.

25 STEP TWO Device Specific Profiles Device Specific Profiles In order to produce either an optimised colour accurate print, or press simulation proof, a device specific profile of your in-house printer is required. The accuracy of Generic Proofer profiles can be determined with the Repro Pack, these results can then be improved by making a device specific proofer profile. Similarly, although scanned images can now be colour corrected from the original scan, this process can be efficiently improved with a device specific scanner profile. Scans may look OK on screen, it is only when an optimised scan of the same image is available for comparison that lost detail and colour variations become apparent.

26 DEVICE SPECIFIC PROFILES Matching your CMYK separations correctly on press is the job of a printing company. However, the profile used to make the separations must be within the tolerances of a CMYK printing press. A print company may be able to supply an appropriate press profile. This will give you the ability to see an accurate soft-proof on your monitor. Alternatively, a print company should be able to match to either Photoshop Euroscale v2 (in Europe, or US Sheetfed Coated v2 in the USA), or for superior results try the ColourConfidence PressMatch profile which comes free with the Colour Confidence Repro Pack. Profile building software can be categorised as 2 levels. 1) Design and artwork where accurate Monitor, Scanner and Proof printer profiles are required but control of building specific press separation profiles is not required. 2) Reprographic studio and Print Company profiling. In addition to the requirements of level one, more sophisticated profile building control is required, for printing presses or high end digital devices. Monitor and Scanner profiling is generally of a similar standard for both levels of user. It is important to calibrate (linearise) scanners and printers before profiling.

27 SCANNER PROFILING Scanner Profiling To build a scanner profile a reference target is required.these are known as scanner IT8 targets and comprise of 264 colour samples and an associated reference file.the reference files contain the Lab colour values of each colour sample.to avoid the expense of a special colour measuring device (spectrophotometer), to handle both reflective and transparent material (as described later in this document), measurements are available to cover batches of targets.these colour values are averaged measurements from the manufacturer, based on a production batch. Different scanner profiles, and in-turn IT8 targets, are required for reflection prints and transparencies. Having calibrated the scanner, an IT8 target is scanned as an RGB image and the profile building software builds a table to convert between the scanned RGB values and the correct known Lab values in the reference file.this being the scanner profile.

28 SCANNER PROFILING Although the task of building the profile is relatively straight forward, care must be taken in the calibration of the scanner before the profiling process and that settings remain constant for all future scans. Although colour from desktop scanners will vary with time, and ideally scanner profiling should be an in-house facility, it is possible to test the abilities of your scanner before making such a purchasing decision. A scanner profile can be built remotely, by ing a target scan; however, an investment still needs to be made in the actual targets. If such a route is initially taken, products such as On-Target can be used to validate the status of the scanner to avoid reprofiling a scanner unnecessarily. Further details on Desktop Scanner Calibration: Remote Scanner Profiling: On-Target: Scanner Profiling Applications: www. www. www.

29 PRINTER PROFILING Printer Profiling To build a printer profile a series of colour patches, of known CMYK or RGB values, are printed and the Lab colour values measured. For this a colour measuring device (colorimeter or preferably spectrophotometer) is required. It is also possible to use a profiled scanner as a basic colour measuring device. Colour Measuring Devices: Profile building software builds a table converting between known CMYK or RGB values and measured Lab values. A printer profile then has the ability to convert between Lab and CMYK (or RGB) or the reverse back to Lab. Similar to the importance of calibrating a monitor or scanner before profile building, this is also necessary for printers. Unlike monitor profiling that can have calibration built into the profiling process, or scanners with control in the scanner software, there are not always such options for printers.

30 PRINTER PROFILING If not printing through a RIP with calibration/linearisation options, advice is included in Further details on Printer Linerisation or on-line at Remote Printer Profiling.This includes optimisation test charts and how to determine if you should be using an RGB or CMYK printer profile. It is also possible to test the advantages of printer profiling, before making such a purchasing decision. A printer profile can be built remotely, by printing a supplied target and mailing the printed result to a profiling service.the profile is then returned by . It is important to note that although such a procedure should show a justifiable improvement, further improvements should be apparent from the direct control of in-house profile building. Further details on Printer Linearisation: Professional Profiling for Repro: Remote Printer Profiling: Printer Profiling Applications: www. www.

31 ANY QUESTIONS Colour Management is part of your OS, giving you the opportunity to take control of your computers colour. We hope this document has given you the confidence to start benefiting from ICC colour management. If you have any questions or comments regarding this document they may be submitted on-line at: Thank you and please remember to register for FREE updates to this document. Where preferred and for larger projects, world coverage on-site consultancy is also available: Coming soon Windows XP and 2000 Adobe Indesign Quark Express 5.0 Adobe Acrobat TypeMaker Limited 2002

32 Appendix 1 tell me more Device Independent Colour The International Color Consortium (ICC) and Profiles Profile Transformations Rendering Intents System Optimisation & Profile Selection ColorSync Options Monitor hardware settings Monitor Profiling options a, b, c. Application colour settings Desktop Scanner Calibration Printer Calibration/Linearisation Professional Profiling for Repro Colour Measuring Devices

33 DEVICE INDEPENDENT COLOUR A computer monitor (or your television) uses RGB light signals to reproduce colour. Scanners and digital cameras also record colour in this mode. RGB is generally defined within a scale of levels for each of the RGB signals. In terms of RGB, no light produces black 0,0,0, (turn off the lights and you are in the dark), equal combination of all light signals produce white 255,255,255, (switch a regular light bulb on). An imbalance of RGB values produce what we know as colours. For example; Red: 255, 0, 0. or Pink: 255, 127, 127. To lighten the red we add more of the other colours, making it closer to white. LIGHT These values are relative to the maximum achievable by each device. The points of the triangles illustrated above, represent the strongest RGB colours achievable by two devices.the RGB values are scaled from the white/black (centre) to the RGB points of the triangles (yellow scale).an RGB value (e.g. 255, 127, 127), for one device produces a different colour to the other device (blue increments). Continued R B G

34 DEVICE INDEPENDENT COLOUR An inkjet printer, photocopier and digital or traditional printing press, will generally apply colour with CMYK pigments (inks). CMYK is generally defined within a scale of 0 100% of each colour. In terms of CMYK, no colour 0,0,0,0, produces white (or the paper colour before ink is applied) and the more colour (in nearly equal values of CMY) the closer to black is achieved 100,100,100,100. The K (black ink) is added to predominantly reduce the amount of other colours needed. Colour is produced through an imbalance of the CMYK values. Similar to RGB, the CMYK achievable will differ between devices. In both the RGB and CMYK colour models it is also not only the strength (saturation/chroma) of the base colours that can vary. The hue and brightness of the colours also change, so a red may be an orange/red or a violet/red. The scale (or 0 255) may also not be uniform. In printing inks this is called dot-gain where a 50% dot may print as 65% (15% dotgain) and so the whole tonal rage must be compensated for. In the RGB of a monitor, the term Gamma is used to describe such characteristics. C PIGMENT K Y M

35 THE ICC AND PROFILES The ICC and Profiles The International Color Consortium was established in 1993 by eight leading manufacturers in order to create, promote and encourage the standardisation and ongoing development of an open, manufacturer independent, cross-platform colour management system framework. This resulted in the development of the ICC profile specification. A profile can contain input and output tables converting between RGB or CMYK colour values and Lab. Profiles can also contain less channels, such as one in a greyscale image, or more such as 6 channels for Hexacrome separations. A profile is categorised internally as one of the following: Scanner/Digital Camera (input table only), Monitor (in/output tables), Printer (in/output tables) Some RIPs will use Device Link Profiles, which combine both a source and destination profile in one file. Such a profile can have special characteristics such as preserving the black separation channel in a CMYK to CMYK conversion.

36 PROFILE TRANSFORMATIONS An ICC profile transformation is not only applied when an image is converted from RGB to CMYK. Profiles are also used on the fly for displaying an image on a monitor. An RGB image can be converted to CMYK and correctly displayed on a monitor. Or, the process can be reversed from CMYK to RGB. Applications, such as Adobe Photoshop, allow the RGB to CMYK conversion to initially be simulated on the fly.this enables colour correction from the original source RGB data. Continued ORIGINAL R G B Lab R G B MONITOR ORIGINAL R G B Lab Lab DESTINATION C M Y K R G B ORIGINAL C M Y K Lab R G B MONITOR ORIGINAL C M Y K Lab Lab DESTINATION R G B R G B MONITOR MONITOR

37 PROFILE TRANSFORMATIONS Even if you receive a CMYK image file, it is unlikely to be CMYK optimised for your print process. Even if it displays correctly (visually acceptably) on screen, this may be simulating the CMYK print characteristics of the originator s embedded profile and not your process. A CMYK to CMYK profile conversion is an efficient and ideal method to correct for differences in the CMYK print processes. ORIGINAL C M Y K Lab DESTINATION C M Y K Lab R G B MONITOR

38 RENDERING INTENTS Rendering intents apply a combination of the following transformations; Gamut Compression Scaling the colour gamut of the input profile to the achievable gamut of the destination profile. Tone Compression Scaling the tonal range of the input profile to the achievable range of the destination profile. Gamut Clipping If no Gamut Compression is applied, any colour in the input profile not achievable in the destination profile will be clipped to the closest achievable colour. White-Point Mapping The White-Point in a profile defines the lightest point achievable.this is the white of the paper defined in a printer profile and the target display white point in a monitor profile.when simulating a print process through a monitor profile, or a press profile through a proofer profile, white-point mapping helps achieve an accurate match. Continued

39 RENDERING INTENTS Rendering intent options are as follows and it is important to use the most appropriate for each task as required: Representations of a source RGB profile (red) and destination CMYK profile (blue) illustrate how the rendering intents manipulate colour between gamuts. APPENDIX 1 APPENDIX 1 Perceptual rendering intent All the colours within the source colour gamut are scaled to fit within the gamut of the destination profile, whilst retaining the relationship of colours within the image. Generally used when converting an image from a large to a small colour-space, such as an RGB scan to a CMYK print. Continued

40 RENDERING INTENTS Relative Colorimetric rendering intent In gamut colours remain unchanged but any out of gamut colours (illustrated in grey) will be clipped. Clipping will flatten a colour when maximum saturation has been achieved, or a incorrect colour is added to darken the image in an attempt to boost saturation. Differences in the profile s white points (paper colours) are ignored. Most appropriately used when converting into a larger gamut profile (in which there would be no gamut clipping) to simulate the accurate colour values of the source profile. The illustrated effect of converting from a larger to a smaller gamut is not recommended for this rendering intent. However, proof printers generally have a similar or larger colour-space than the printing press. For example if the larger (Adobe RGB) gamut was our proofing device, then a Colorimetric rendering intent could be used to convert from the smaller Euroscale gamut. Continued

41 RENDERING INTENTS Saturation rendering intent Stretches/squashes the source gamut into the destination gamut producing the most vibrant colour range achievable, but distorting the relationship of colours. More appropriate to graphics, as in PowerPoint presentations etc, than to photographic images or logos etc. Absolute Colorimetric rendering intent As with Relative Colorimetric, in gamut colours remain unchanged but any out of gamut colours will be clipped. Differences in the profile s 'white points' (paper colours) are accommodated. Most appropriately used when converting into a larger gamut profile to simulate the accurate colour values of the source profile, when the paper colour is also important. For example the simulation on white copier paper of how an advertisement will look on off-white newspaper.

42 SYSTEM OPTIMISATION & PROFILE SELECTION ColorSync and OS X ColorSync is far more integrated into the operating system under OS X than under OS 9, but the general principles as how it works are the same. Each device (e.g. scanner, monitor or printer) can have a profile associated with it, as can documents (e.g. PDFs,TIFFs etc.). Scanner and printer profiles created under OS 9 can be used under OS X as long as all the device settings remain the same. Monitor profiles should be created under the appropriate operating system. This section will deal with ColorSync 4.1, part of Mac OS ColorSync options can be set within the ColorSync Preference Pane in System Preferences for general default settings, within the Displays Preference Pane for monitor profiles and within the ColorSync Utility for device profiles.the ColorSync Utility also has a number of tools to help you work with profiles. Profiles in OS X need to be stored in one of three separate folders: System/Library/ColorSync/Profiles - This is for Apple s generic profiles only and cannot be modified. Library/ColorSync/Profiles - This is the best place to store profiles as they will be accessible to every user of your Mac. User/Library/ColorSync/Profiles - Profiles stored here will only be accessible to the current logged on user. Continued

43 SYSTEM OPTIMISATION & PROFILE SELECTION 1) Default Profiles The Quartz imaging system used by OS X always uses document and device profiles, so it makes sense to set your defaults to match settings in other applications like Adobe Photoshop.Within Photoshop setting your Color Settings to the ColorSync Workflow option will also use these defaults. ColorSync will use these profiles in cases where a document does not have an embedded profile or when a new file is created. RGB Default Select your default source RGB colourspace. e.g. Adobe RGB. CMYK Default Select your default source CMYK colour-space. e.g.your press profile or a generic one such as Euroscale. Gray Default Unless you have a specific grayscale profile this can be left as Generic Gray Profile. See the Photoshop section for how to make a greyscale profile from a CMYK profile. Continued

44 SYSTEM OPTIMISATION & PROFILE SELECTION The CMM s tab offers a choice of Colour Management Modules. At present the OS X only comes with the Apple CMM, others may become available when installed by third-party applications. Select Apple CMM Continued

45 SYSTEM OPTIMISATION & PROFILE SELECTION 2) The ColorSync Utility The ColorSync Utility can be found within the Utilities folder in Applications. It performs three functions: Repairing damaged profiles, providing information on the profiles you have installed, and assigning profiles to devices attached to your Mac, such as Scanner, Cameras and Printers. Profile First Aid - it is unlikely that you ll need to use this very often but if you are having problems with a profile not appearing in your menus, or one that gives very unexpected results, then it may be worth running. Most of the errors it will come up with mean little to all but the most advanced users but if it does find problems clicking Repair will solve most issues. Continued

46 SYSTEM OPTIMISATION & PROFILE SELECTION Profiles - The ColorSync Utility can also give you a lot of information about your profiles; it will tell you what profiles you have on your system and will also give you a 3D graph of a profile s colour space. This graph can be useful for comparing the gamuts of different devices. If you double click on a profile a more detailed window appears giving you a look at the structure of the profile and the various tags within it.this is only really necessary for advanced ColorSync users. Continued

47 SYSTEM OPTIMISATION & PROFILE SELECTION Devices - The ColorSync Utility will also display a list of devices attached to your Mac and the profiles associated with them. Most devices will automatically have an appropriate factory profile installed with the device drivers and this is often selected by ColorSync as the default profile for that device. However you can select another supplied profile or even a custom made profile by clicking on the arrow next to Current Profile. ColorSync will use these profiles when Quartz applications accesses the device, for example when Preview is printing to an inkjet printer, or when Image Capture downloads images from a Digital Camera. However not all applications on your Mac will be using Quartz and you may still have to select the profile for your devices in some programs.

48 SYSTEM OPTIMISATION & PROFILE SELECTION ColorSync Control Panel & Mac OS 9 1) Profiles for Standard Devices These profiles, as illustrated, will be used by the print driver when images need converting on the fly to an output or proofer profile. The print driver also gives the opportunity to make specific choices. Input Select your default source RGB colour-space. e.g. Adobe RGB. Display Indicates your current monitor profile. This is selected through the monitor control panel. Output Select the profile that best describes your final output device (print process). Proofer Select the profile that best describes your proof printer. For profiles to be available for selection in the control panel (and in many applications), they should be stored in the System ColorSync Profiles folder. Continued

49 SYSTEM OPTIMISATION & PROFILE SELECTION 2) Default Profiles for Documents These profiles, as illustrated, can be used as defaults when opening an image that has no embedded profile or when creating a new image file. In applications such as Adobe Photoshop setting the ColorSync Workflow option will use these defaults. RGB Select your default RGB working colour-space. CMYK Select your default CMYK working colour-space, such as your final print profile. GRAY See Photoshop info later for how to make a greyscale profile from a CMYK press profile. Lab ColorSync includes the Generic Lab Profile. Continued

50 SYSTEM OPTIMISATION & PROFILE SELECTION The CMM s tab offers a choice of Colour Management Modules. Some, such as Apple CMM, are installed as part of ColorSync, others become available when installed by third-party applications. Select Apple CMM

51 SYSTEM OPTIMISATION & PROFILE SELECTION Windows XP and 2000 Information about colour management under Windows XP and 2000 is currently available on-line and will be included in the next release of this document. All colour management theory and information on application settings are still relevant. Click on the weblink below. Then...

52 COLORSYNC OPTIONS Default Profiles for Documents The RGB and CMYK default profiles set here are the assumed profiles of images opened into documents and for opening new documents for applications that use ColorSync. For example, the Photoshop colour settings include the option of ColorSync workflow. Based on this, opening an RGB image into Photoshop would assume the ColorSync RGB default profile and the equivalent for CMYK. Linking application colour defaults back to the ColorSync defaults (ColorSync Workflow) can help reduce the possibility of errors due to different colour settings between applications. However, until a time when all applications have the same ColorSync Workflow option, this is not too helpful. Similar to this, Adobe have linked all their applications with shared colour settings files.these are more comprehensive than the ColorSync Workflow defaults, as covered in how to set up Photoshop.

53 COLORSYNC OPTIONS CMM Selection Selecting Automatic will use the default CMM of the profile being used if it is installed. A specific CMM can also be specified here. Initially we suggest selecting the Apple CMM for Macintosh ColorSync. If however, a process further down the workflow is known to work only with a specific CMM such as Kodak or Heidelberg in a windows environment, then it may be appropriate to choose such a CMM on your Macintosh workstation also. A further CMM, which cannot be selected from this menu, is the Adobe CMM (ACE).This can only be used for conversions within an Adobe product and we recommend it for all conversions within their applications.

54 COLORSYNC OPTIONS Default Profiles for Documents The RGB and CMYK default profiles set here are the assumed profiles of images opened into documents and for opening new documents for applications that use ColorSync. For example, the Photoshop colour settings include the option of ColorSync workflow. Based on this, opening an RGB image into Photoshop would assume the ColorSync RGB default profile and the equivalent for CMYK. Linking application colour defaults back to the ColorSync defaults (ColorSync Workflow) can help reduce the possibility of errors due to different colour settings between applications. However, until a time when all applications have the same ColorSync Workflow option, this is not too helpful. Similar to this, Adobe have linked all their applications with shared colour settings files.these are more comprehensive than the ColorSync Workflow defaults, as covered in how to set up Photoshop.

55 COLORSYNC OPTIONS CMM Selection Selecting Automatic will use the default CMM of the profile being used if it is installed. A specific CMM can also be specified here. Initially we suggest selecting the Apple CMM for Macintosh ColorSync. If however, a process further down the workflow is known to work only with a specific CMM such as Kodak or Heidelberg in a windows environment, then it may be appropriate to choose such a CMM on your Macintosh workstation also. A further CMM, which cannot be selected from this menu, is the Adobe CMM (ACE).This can only be used for conversions within an Adobe product and we recommend it for all conversions within their applications.

56 MONITOR HARDWARE SETTINGS Monitor Hardware Settings The starting point for most methods of monitor profiling is to select the appropriate hardware white-point.this option is generally available with most higher end monitors. The physical controls on the monitor (in addition to brightness/ contrast) may let you select a white-point of 5,000K, 6,500K or 9,300K. Select the desired setting. Choose 5,000K if matching to proofs in an equivalent viewing booth, or 6,500K may be more appropriate if in natural office lighting. If you do not have such options, profiling can also target a white point lower than that of the hardware default. These are generic hardware targets and some profiling applications have options to measure the actual white point of the monitor and then if the monitor hardware allows, adjust the individual R, G, B white values to match the perfect white-point.

57 MONITOR PROFILING Software based monitor profiling, option A The Apple Monitor Calibration Assistant is accessed through selecting Calibrate in the Colour section of the Monitor Control Panel or Displays Preference Pane. The Expert mode checkbox enables extra options but it is advisable for first time users to familiarise themselves with the process without these options. The wizard approach explains what is required at each stage, resulting in the creation of an ICC profile for your monitor. Continued

58 \ MONITOR PROFILING Software based monitor profiling, option B The Adobe Gamma Step by Step (Assistant) profiler is accessed by selecting Adobe Gamma in the Control Panel and proceeding through the Step by Step wizard. This produces similar results to those achieved from using the Apple Monitor Calibration Assistant, but this method is slightly more technical. Continued

59 MONITOR PROFILING Instrument based monitor profiling, option C Using a colour measuring instrument (colorimeter or spectrophotometer) to build a monitor profile combines accuracy with repeatability, reducing the subjectivity of the process. A series of known RGB colour values are displayed on the monitor and the instrument measures and records the Lab value for each colour. Before the colours can be measured, the hardware white point of the monitor will require setting, the brightness and contrast optimising and a profile target white point and gamma value selecting. A single instrument can generally be shared across as many workstations as appropriate (e.g. up to 5), but multiple software licenses are normally required. Monitor Profiling: www.

60 APPLICATION COLOUR SETTINGS Adobe Photoshop Elements This limited functionality version of Adobe Photoshop includes similarly limited colour management options. The application s colour modes are restricted to RGB (and index colour), which eliminates the complexities of CMYK colour management issues. Colour Settings (Edit Menu), offers three levels of colour management. None, Limited and Full. Switching between these options will change how the colours in an open image are interpreted, resulting in the display changing. None assumes that the RGB image values of the image are the exact values for the monitor display. Limited, assumes the image profile to be srgb, this being the colour space standardised for www. Full (colour management) is similar to limited,other than the assumed profile is Adobe RGB, this being a larger RGB colour-space and more appropriate for CMYK print processes. The option to embed the image profile (srgb or Adobe RGB) is given at the point of saving the image. In order to print a colour managed image we suggest using the following option in the print menu. Continued

61 ADOBE PHOTOSHOP ELEMENTS Print menu options Adobe Photoshop Elements If the document to be printed has been saved to include the RGB profile (srgb or Adobe RGB), this is indicated as the source space. The Print Space can be selected from any RGB or CMYK printer profile and an appropriate rendering intent. Continued

62 ADOBE PHOTOSHOP ELEMENTS Although there is no option to select the CMM in this window, the Adobe (ACE) CMM is used. The selected print driver may also include Colour Management options under a heading such as Colour Matching.This could include similar options to those in the Adobe application specific window, however we initially recommend using the Adobe options as illustrated. The options relating to saving the print settings as a default will vary on the active print driver.

63 APPLICATION COLOUR SETTINGS Adobe Photoshop v6 & v7 The main Colour Settings window is opened from the applications Edit menu, or in the Photoshop menu under OS X.These settings help to ensure that images are opened and converted correctly. Setting the Proof Setup window from the View menu correctly and the associated Proof Colors option are crucial to achieving an accurate on screen proof. To setup the Color Settings window as illustrated on the following page, select Europe Prepress Defaults in the top settings menu (Or US Prepress in the USA).This will display the defaults as illustrated. If the majority of profile conversions are to be RGB to CMYK, change the rendering intent to Perceptual. If you have the CC PressMatch profile (from the Colour Confidence Repro Pack) or another press separation profile, this can be set as the working space CMYK default. If the majority of your conversions are to be based on simulating a smaller gamut image into a larger gamut profile, then Relative Colorimetric may be more appropriate. Either way, when a conversion is requested through the Convert to Profile option, the user is prompted to confirm (or change) the intent to be used. However, a straight RGB to CMYK mode change does not give this choice or indicate what is being applied. Continued

64 ADOBE PHOTOSHOP Save the settings under an appropriate name, in the System Folder (or Library in OS X) / Application Support / Adobe / Color Settings.The settings file can now also be used with Adobe Illustrator and loaded on other workstations. Please note that if Advanced Mode is not checked, only reduced options are available and profiles can only be selected from Photoshop defaults, profiles in your ColorSync folder will not be available for selection. Continued Rename Check On Change to your Final Output CMYK separation profile. If not available, use the settings default profile. (Euroscale or US...) Change to Perceptual explained overleaf

65 ADOBE PHOTOSHOP Of the four Rendering Intents, Photoshop s Conversion Options default is Relative Colorimetric. Selecting the Use Black Point Compensation option with a colorimetric conversion enhances results, combining some of the benefits of the Perceptual intent. Converting to a smaller gamut profile (an RGB to CMYK conversion), using a Colorimetric intent could cause clipping of some colours. Selecting Use Black Point Compensation with the Colorimetric intent eliminates the clipping (flattening) of out-of-gamut shadow tones.the black point of the source profile is scaled to match the destination profile, similar to using the Perceptual intent. This method produces a better match to original colour than from the Perceptual intent, without the problems of clipping shadow areas as from the standard Colorimetric intent. However, out of gamut saturated colours can still become flattened, but not all images will contain such colours. So, if you don t intend to spend too long on evaluation of each image, the Perceptual intent is advised as the default RGB to CMYK conversion method. Continued

66 ADOBE PHOTOSHOP When opening an image in Photoshop, you may be prompted with one of the following situations. a) The documents embedded profile does not match the current RGB working space. Open based on the embedded profile to view the image as seen by its supplier. If it does not look ideal, assigning different source profiles may improve your starting point and then convert into your working RGB space if desired. b) The RGB document does not have an embedded profile. If this is an image you have scanned, you should apply the appropriate scanner profile and if desired convert into your Photoshop working RGB colourspace. It is generally easier to work with all images in a single RGB colourspace. If this image was supplied in its digital form and you have no experience of an appropriate profile for images from this supplier, start by assigning your working RGB colour-space. For CMYK images that were scanned to a specific CMYK specification (such as Euroscale Coated v2, or your specific press profile), assign the appropriate profile so it will be displayed as it will print. Continued

67 ADOBE PHOTOSHOP For unknown CMYK files, we recommend starting by assigning the profile of how the file will print (possibly your working CMYK profile). If having assigned your working profile (CMYK or RGB) the image colours do not look correct, using the Assign Profile option in the Image / Mode menu see if a different profile is more appropriate for the image. Following this, use Convert to Profile to adjust your image for your correct colour-space. To view an active CMYK image correctly as it will print, select Simulate Paper White from Proof Setup in the View menu.the display will toggle into Proof Colours (command Y) mode and include the correct background paper colour in the display. However, to accurately display how an active RGB document will print based on a CMYK profile, go to Custom in the Proof Setup menu. Select the desired CMYK destination profile, Perceptual intent and Simulate Paper White. These settings can be saved for future use and Command Y will toggle to the preview. Continued

68 ADOBE PHOTOSHOP Or, to view how a CMYK file will print to a proofing device (or a different printing press) without any further colour conversion, go to Custom and select the new CMYK destination profile and check the Preserve Colour Numbers box.this can similarly be applied to an RGB file when an RGB destination profile is also selected. Two other menu options relevant to the use of profiles are in the Image/Mode menu.these are Assign Profile and Convert to Profile Assign Profile will assign a selected profile to an image.this will not change the RGB or CMYK image values, but will change the way those values are interpreted, resulting in a change in the perceived colours in the image. Assigning a different profile may be used if an image is received and when correctly viewed on your profiled monitor (or printed to a profiled printer) the image colours look incorrect. Before colour correcting by adjusting the image colour values it may just be that the image has been interpreted through the wrong source profile. Even if the image included an embedded profile it could quite easily be incorrect. Continued

69 ADOBE PHOTOSHOP Assigning different profiles will not change the image data but will give you the opportunity to interpret the image in its ideal form. However, this procedure is not ideal as when switching between views it is not easy to judge which looked best. Switching the Preview check box on and off shows a quick comparison between the current and new profile s interpretation of the image colour values. The application What Profile? resolves this issue. A single image is displayed 4-up based on different source profiles (RGB/CMYK) with the option to assign the most appropriate. For more details on the other features: What Profile? www. Continued

70 ADOBE PHOTOSHOP Convert to Profile changes the pixel values in your image file, based on a conversion between the current source profile and a selected destination.this could be converting from an RGB to CMYK colour model,cmyk to RGB, RGB to RGB, or CMYK to CMYK. To apply a conversion both a CMM and appropriate rendering intent must be selected. As suggested for the colour setting defaults, select the Adobe (ACE) CMM. Continued

71 ADOBE PHOTOSHOP The choice of rendering intent should be determined based on the combination of source to destination profile. As previously described, technically if the source profile has a larger gamut than the destination gamut (most common with an RGB to CMYK conversion), the Perceptual intent should be most appropriate. If converting from a CMYK press colour-space to a larger CMYK proofing colour-space, then a Colorimetric intent may be more appropriate. When converting into a smaller gamut, the Photoshop option of Black Point Compensation makes it possible to take advantage of colorimentric intent colour matching whilst eliminating potential clipping of out of gamut shadow tones. However, the preview check box should be used to ensure areas of saturated colour are not being flattened. If so, the Perceptual intent may be more appropriate. The Use Dither option produces smoother conversions from blends and should generally be used. Following an image conversion, particularly when the result is in CMYK, make sure the Proof Setup (Proof Colours) settings are as desired, such as to simulate the printed results, including paper white simulation. Continued

72 ADOBE PHOTOSHOP Printing from Photoshop The Photoshop print options include the ability to apply a profile conversion on-the-fly as you print.this avoids the necessity to convert your image into a proofer colour-space, which could vary with time. The example indicates that an image in the Adobe RGB colour-space, with a proof setup of Euroscale Coated v2, will print to simulate (Absolute Colorimetric intent) the Euroscale on to the proofer profile. Had the Document: Adobe RGB button been selected with a Perceptual intent, the conversion would optimise the original RGB image for the colour gamut of the proofer, ignoring any influence of the Euroscale profile. To simulate the results of a CMYK source image, the Document Source should be converted with Absolute Colorimetric to the proofer profile. or Continue for Adobe Illustrator and Quark Xpress

73 ADOBE ILLUSTRATOR Adobe Illustrator v9 & 10 If colour settings have already been defined for Adobe Photoshop, this colour set can be saved and loaded into Adobe Illustrator Color Settings in the Edit menu. Otherwise it should be set to Europe or US Pre- Press: Change to your Final Output CMYK separation profile. If not available, use Euroscale in Europe or US Web /Sheetfed in the USA. Change to srgb if you are designing web graphics. Continued

74 ADOBE ILLUSTRATOR Adobe Illustrator v9 & 10 Illustrator has many of same functions as Photoshop - you can use Proof Setup to get a better idea how your graphic will print. You can assign the correct profiles for your graphics so that they travel smoothly through your colour workflow. And you can convert between profiles as you print so that you get the most accurate proofs of you documents. or Continue for Quark Xpress

75 APPLICATION COLOUR SETTINGS Quark Xpress v4 Quark Xpress ICC colour management is an Xtension that must be first selected in the Utilities / Xtensions Manager menu. Colour Management preferences can then be set in the Preferences section of the Edit menu. If no document is open the new preferences will be applied to all new documents, or if a document is open, only to the current document. Colour Management can then be switched on/off in this preference window. A reason for switching colour management OFF is if your document has been prepared in its final CMYK separation colour space and you want to be sure no further profile conversions are applied on the way to print. Similarly if you are applying colour management conversions on the RIP of a printer and do not want the possibility of additional conversions. Switching Colour Management ON activates a range of settings. Continued

76 QUARK XPRESS v4 Your display profile should be selected for the Monitor,Proof Printer profile for Composite and Press profile for Separation Printer. The separation profile is only used when CMYK separations are printed. For general printing the Composite profile will be used optionally simulating the results of the separation profile if instructed in the print dialogue. Default Source Profiles; your Photoshop default RGB profile, such as Adobe RGB should be selected in the RGB tab. Similarly your default press profile (e.g. Euroscale v2) for the CMYK tab.the Colour line refers to Xpress generated vector work and Image to pixel data. Display correction indicates if the display should simulate the Separation profile as for press separations, or the Composite profile if this has been defined to describe the final reproduction process. Continued APPENDIX 1 APPENDIX 1

77 QUARK XPRESS v4 The Display Correction can be limited to specific colour models by checking the list accordingly. When Colour Management is switched on, the print dialogue includes a Profiles tab.this defaults to the preference settings for profiles, with the added option of a check-box instructing Composite Simulates Separations. When this is checked, a composite proof will simulate the final separations profile colour-space. For example as configured in the illustration, the default source profile for CMYK images is Euroscale v2, the check-box will apply a colorimetric conversion between that profile and the proofer profile. Similarly an RGB image would be converted from Adobe RGB into Euroscale and then out to the Proofer profile. Continued

78 QUARK XPRESS v4 To ensure an accurate display of supported file formats, it is a recommended and practical procedure to convert all images into your selected default RGB and/or CMYK colour-space before placing them into Quark. Unfortunately Xpress v4 is limited in the format of images/graphics to which it can apply colour management, so the colour management options frequently remain switched off. The main limitation is the inability to apply colour management to EPS files (cont. tone or vector graphics). Xpress can not display such images colour corrected or apply a colour conversion within the application during the print process. However, if printing through an ICC aware RIP, the conversions can be applied at this stage. The above limitation can also be avoided by using third-party Xtensions that enhance the colour management abilities of Xpress. For further details: www.

79 SCANNER CALIBRATION Desktop Scanner Calibration Scanners have a variety of different options for calibration, these being the image adjustment controls in basic scanners. The following points will help in optimising your scanner for profiling: Switch off all automatic compensation tools, colour correction, auto highlight/shadow and USM (UnSharp Masking). Identify the tools that allow the setting of manual highlight/shadow and also mid-tone which may be referred to as exposure or Gamma. Scan the IT8 target and check the RGB colour values of the lower grey ramp in Photoshop or equivalent application or scanner software (using the colour picker and info palette). The RGB values of the white patch should be in the range of 245/250 with slightly lower values in the adjacent patch. At the other end of the scale the black patch RGB values should be in the range of 5/10 with slightly higher values in the adjacent patch. APPENDIX 1 Continued

80 SCANNER CALIBRATION Adjusting the Highlight/Shadow settings and rescanning will optimise the scanner to this range. Linearisation patch number 11 should be in the range of 120/135. To achieve this, the mid-tone/exposure setting (possibly called gamma) can be adjusted. A scan falling into the above categories should indicate a well calibrated scanner. The IT8 scan can then be used to build a profile and the same setting should be used for all future scans. Different scanner settings will normally be required to achieve similar calibrated results for profiling (and using) other media (reflection/transparency). APPENDIX 1

81 COLOUR MEASURING DEVICES Colour Measuring Devices Building a profile requires an accurate colour measuring instrument. Colour measuring instruments fall into one of the following three categories which describe the type of colour data captured: Densitometer A Densitometer records how dark a colour is. Different colours may have the same density. Density is generally used when working with inks of a known colour, to measure the amount of colour applied. Densitometers are not suitable for building colour profiles but can be used for device calibration. To recalibrate (NOT profile) a proofing device, colour densities can be measured and a correction for any drift applied. Density is used for measuring the control strip on a press sheet (a solid and possibly 75%, 50% and 25% patches). Density values are also used to check that film separations and printing plates are prepared to the correct exposure. Continued

82 COLOUR MEASURING DEVICES Colorimeter A Colorimeter records colour in a similar manner to how the eye filters colour into regions of Red Green and Blue.Through measuring the levels of these three colour components a colour can be represented in terms of the Lab colour space. A Colorimeter can be used to measure colour for building a profile, however the colour values recorded by a spectrophotometer are better and will contribute towards producing a generally more accurate profile. Spectrophotometer A Spectophotometer measures a colour s spectral data.this being the intensity of light reflected from a colour sample at a number of points along the visible spectrum.this data is interpreted in the form of a spectral curve showing the reflectance intensity of the colour at different wavelengths. So, unlike colorimetric data which records the balance of RGB in a colour (3 regions), spectral data records values at many points along the visible spectrum, ranging from Violets, through Blues, Greens, Yellows, Oranges to Reds. Continued

83 COLOUR MEASURING DEVICES From spectral data accurate Lab colour values can be calculated and also colorimetric and densitometric values. Measuring through optional UV filters helps eliminate the effect of non visible Ultra Violet wavelengths being distorted into the visible spectrum and influencing colour readings. A spectrophotometer is the ideal device for profile building. For each type of measuring instrument there are both hand-held and automated devices available. A hand-held device requires manual alignment of the device on each colour patch to be measured a run of up to 300 patches is acceptable but hard-going. An automated device can either read strips of colour patches (a strip reader), requiring alignment of each strip of multiple patches, or a complete sheet (X-Y table). Continued

84 COLOUR MEASURING DEVICES Other device specification options: Measuring devices can read either reflective and/or transmissive colour (e.g. colour measured from a print and/or monitor). For transparency measurements a transmissive device also containing a controlled light source is required. Desktop colour management generally requires a reflective model for measuring colour patches printed on paper and transmissive for monitors. Although building a transparency scanner profile requires a transparency IT8 target with Lab reference values for each patch, these targets are available with an associated set of measurements.these readings may not be as accurate as measuring oneself, but the values are within an accepted tolerance and avoids the unnecessary expense of an appropriate special transmissive device also containing a controlled light source. A compromise to also avoid purchasing even the most basic of Colorimeters is to use ones profiled scanner to measure colour values for building a printer profile. Continued

85 COLOUR MEASURING DEVICES Making your scanner a colour measuring device Just as a colour measuring device interprets colour patch values in the Lab colour-space required to build a profile, the same can be achieved through a profiled scanner.the results will not be perfect but better than nothing. Scanning in RGB and applying the appropriate scanner profile will convert the RGB scan values into the Lab colour-space. However, the accuracy will not be as good as using either a spectrophotometer or colorimeter. The accuracy of the RGB values is based on the limitations of the scanner and accuracy of its profile. Such factors combined, reduce the accuracy of your measurements but will still produce useable data. Measuring instruments: Printer profiling from your scanner: www. www. Continued

86 PRINTER LINEARISATION Printer Linearisation In order to build a good printer profile the device must first print reasonably linear and the same settings used for ongoing proof printing. The objective of linearisation is printing sets of C, M, Y and K patches at 5% steps from 0% to 100% and to visually be able to identify a difference in each step. For example the first visible colour being in the 15% patch would not be ideal and neither would the 70% patch becoming a solid as heavy as the 100% patch. Profiling your printer under such conditions is restricted to compressing separations to the 55% range from 15% to 70%. Separations should ideally uniformly cover the whole 100% range. Some RIPs have linearisation options built in for the printers they drive, however many models and direct print drivers do not have such options. Continued

87 PRINTER LINEARISATION In such circumstances there are generally choices available in the print driver print options, such as plain paper/gloss paper, or, fine/regular print mode, etc.these options are given by the manufacturers to control the ink flow to the varied range of papers the device may be used with. It is advisable to experiment with all print options to get a visually good linear print before printing colour patches to build a profile.this is especially important for remote profiles where you do not have direct control over the final profile. A test chart and further guidance on optimising your print driver settings is available from: Proofer Optimisation www.

88 PROFESSIONAL PROFILING FOR REPRO Profiling for Reprographics A profile determines what colour values are required to achieve a specific colour for a particular device/process. Using the CMYK (Cyan, Magenta,Yellow and Black), 4-colour process, the same colour can be achieved through different colour combinations.this is determined by the amount of black used. Black can be achieved from a combination of only CMY or the black colour itself.this does not only relate to producing areas of black in an image but also the black content of both grays and colours. For example a dark red colour may be reproduced from 90% M, 80% Y and 30% C.The two higher value colours (M and Y) determine that the colour will have a red hue and the C neutralises an amount of this colour to make it a dark red. It is therefore possible to use k (Black) to replace some (or all) of the C and appropriate amounts of M and Y. This reduces the amount of ink required for print. For quality offset printing neutral grey colours are generally made from predominantly the CMY colours, with K introduced in the darker shades.whereas in non neutral colours, such as the dark red example, black will be used where possible to reduce the CMY values and sometimes totally eliminate the lowest colour value (the shadow content). Continued

89 PROFESSIONAL PROFILING FOR REPRO This process is knows as UCR (Under Colour Removal). For newspaper separations, where black is used to a maximum wherever possible in both colours and neutrals, the process is known as GCR (Grey Component Replacement). Control of the above and other factors such as the maximum ink to be used to produce the darkest black (total ink) and the maximum value of the black separation can all be set as separation characteristics of a printer profile. The complexities of a press profile are not generally relevant to many desktop printers. Most simple colour inkjet printers are developed to work with RGB profiles and the conversion to CMYK is preset in the print driver. For other devices, such as colour copiers, the default options of lower level profiling applications will generally produce satisfactory results. However, for the more sophisticated inkjet and contract proofing devices, professional control of profile building is generally required.

90 Appendix 2 On-line product details Click for up-to-date on-line product details TypeMaker Limited 2002