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5.3 Adobe Photoshop
Adobe Photoshop supports RGB, CMYK and CIE Lab colour spaces and has a wide range of specialist colour matching palettes including Pantone, Trumatch, FocoTone, TOYO and ANPA_COLOR. It functions as a generic CMS as described in section 2 and is believed to be based on Kodak.
When selecting or creating a colour, Photoshop has a gamut alarm if the colour can not be produced on the output device. The closest matching solid colour is displayed next to the alarm symbol.
Adobe PhotoShop supports RGB, CMYK and CIELab (a visually uniform transformation of CIE XYZ space for surface colours) device independent colours. CIELab is recommended for moving images between systems, and for printing to Postscript level 2 printers.
As in other Colour Management Systems, the system in Adobe Photoshop contains a set of device profiles. Photoshop also allows the user to calibrate the colours, either by using specific tools, or by visual comparison with a calibrated monitor.
When using Photoshop colour calibration, the user creates a preference file that contains calibration information on the display device and printer combination. The calibration menus include many devices, but also allow for custom settings. The user needs to create a preference file for each combination of printer and monitor in use. The monitor calibration information also contains a setting for ambient light, as this affects how colours appear. Different files are therefore required if the lighting conditions are varied.
The basis of the Adobe system is the monitor calibration.
The user has options to calibrate gamma, color balance, and white and black reference points. The Monitor calibration program allows the user to match the white reference point to white paper colour. Gamma, colour balance and black reference points are calibrated using the mouse and slider bars. The user visually matches grey areas on the display.
Since the white reference point is obtained by visually matching white on the display to white paper, Adobe recommend saving and loading custom calibration settings for each different paper stock. Once a monitor is calibrated, a Monitor setup can be generated, including the ambient light information. Custom values supplied by the manufacturer can also be entered.
Once the monitor is defined, then the user can progress to printing ink setup. Again, there is a list to choose from or the user can create custom definitions.
Setting printing inks allows for the input of CIE colour values and for dot gain percentage. The user interface is via mouse driven windows. Once a basic setup is defined, the user can create a colour proof. The user can then adjust the calibration settings until the on-screen image visually matches the proof.
If the user is using a set of printing inks that are not listed in the Inks Setup menu, then he/she can create a custom set by one of three methods.
Adobe Photoshop can print the CMYK image as one image or as four separate images. This is an option in the print menu. In some cases the user may want to adjust the way the CMYK plates are generated by adjusting black generation and undercolour removal parameters. There are two options, undercolour removal (UCR) and grey colour replacement (GCR). GCR is the default method and is used for coated stock. UCR is the best choice for uncoated stock and newsprint. Adobe PhotoShop allows the user to specify the degree of black generation, and the total ink limits. Once this is done, the user can then specify Light, Heavy, Medium or Maximum black generation. This produces a base line curve. The user can then use the mouse to alter this curve, and the colour proportions are adjusted accordingly.
Photoshop allows the creation of a curve that corrects colour cast on scanned images.
Unlike the three packages discussed more fully in the preceding sub-sections, information on this package was not obtained by demonstration, but simply sales literature. It is, however, indicative of what will become a more prevalent feature of such image editing packages. It contains a full integration of the Kodak Precision Color Management System as outlined in sub-section 4.3. Therefore users can expect access to all the features that CMS offers. In how usable a manner those features are provided can only be determined by inspection.
- Check whether Adobe has a set of Photoshop colour patch values. The menu only lists the most commonly used ink sets and printers. Other sets are available.
- Use a colorimeter to obtain the CIE values of each of the patches in the proof.
- Select a colour patch and adjust the colour on-screen until it matches the proof.