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Inside Macintosh: Advanced Color Imaging on the Mac OS /
Chapter 4 - Developing ColorSync-Supportive Applications / Developing Your ColorSync-Supportive Application

Providing Soft Proofs

Using the ColorSync Manager, your application can provide your users with a soft-proofing feature to enable them to preview the printed results of a color image on the system's display or local printer without actually outputting the image to the printer that will produce the final image. The destination printer's profile provides the ColorSync Manager with the information required to determine how the colors of the image will appear when printed. You can soft proof an image by showing on the system's display the outcome a printer would produce because most displays support a wider color gamut than do printers. Therefore, a display will probably be able to show all the colors a printer could support.

Providing a feature that simulates the printed outcome for the user to preview can save users considerable time and cost by allowing them to intervene and adjust colors before sending the image to a printing shop. For example, without the ability to soft proof and correct the colors of an image using a color management system such as the ColorSync Manager, a graphics designer producing a poster to be printed by a printing press would require the services of a prepress shop to achieve the correct results before sending the image to the printing press. The graphics designer might print the image to a local desktop printer with a color gamut more limited than that of a printing press and then submit the output to the prepress to correct the colors, repeating this process until the results were satisfactory. Your application can eliminate the need for the intermediate steps by allowing the user to color match the image to the color gamut of the final printing press, display the image, and adjust the colors accordingly.

You can use the low-level ColorSync Manager color-matching functions CWMatchPixMap and CWMatchBitmap to perform the color matching, or you can match a list of colors using the CWMatchColors function. To use these functions, your application must first define a color world that encompasses the profiles for the devices involved in the soft-proofing process.

For example, suppose your user intends to create a color image by drawing to the display, then color matching the image to the color gamut of the printing press and printing the image to a local desktop printer before delivering it to the printing press. The user intends to repeat this process until he or she is satisfied with the color rendering. To allow the user to do this, your application must build a color world using the system profile for the display device, the profile for the printing press, and the profile for the local desktop printer; you must specify the profiles in processing order. Because the process involves three profiles, your application must use the CWConcatColorWorld function to set up the color world. "Creating a Color World for Color Matching and Checking Using the Low-Level Functions" (page 4-25) describes how to set up a color world.

You can preserve the series of profiles from a soft-proofing process for future use by creating a device-linked profile representing the configuration and passing the device-linked profile to the CWConcatColorWorld function to set up a color world. For information on how to create and use a device-linked profile to build a color world, see "Creating and Using Device-Linked Profiles" (page 4-52).

Your application can also use the high-level QuickDraw-based NCMBeginMatching and CMEndMatching functions for soft proofing of a color image drawn to the display that your user wants to color match to the gamut of a printing press and print to a desktop printer.

The NCMBeginMatching function matches the colors using the two profiles that you specify, and the CMEndMatching function terminates the color-matching session. Because the NCMBeginMatching function takes two profiles only--a source profile and a destination profile--you must call sets of these functions to enact soft proofing.

QuickDraw matches to the most recently added profiles first. Therefore, to use the NCMBeginMatching and CMEndMatching pair to perform soft proofing from a displayed image to a printing press output image to a desktop printer image, you would first call the NCMBeginMatching function with the printing press to desktop printer profile references and then call NCMBeginMatching with the display to printing press profile references. QuickDraw will color match all drawing from display to printing press and then to the desktop printer.

To use the NCMBeginMatching function, you specify the source and destination profiles. Passing NULL as the source profile assures that the ColorSync Manager uses the system profile as the source profile. Similarly, passing NULL as the destination profile uses the system profile as the destination profile.

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© Apple Computer, Inc.
13 NOV 1996