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The Critically Important Color and Gamma Calibration Article

This article will explain how to understand and work with Photoshop's Color Management System (CMS), including how to create a custom profile, how to create an ICC profile for a monitor, how to set Photoshop's CMS defaults, how to use the Color Settings dialog box, and much more. It is excerpted from Inside Photoshop CS, by Gary D. Bouton. (Sams, 2004, ISBN: 0672326442).

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By: Sams Publishing
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December 15, 2004
  1. · The Critically Important Color and Gamma Calibration Article
  2. · Understanding Photoshop's Color Management System (CMS)
  3. · International Color Consortium (ICC)
  4. · Translation, Please
  5. · Preparing to Create a Custom Profile
  6. · Install the Latest Drivers for Your Equipment
  7. · Setting Photoshop's Color Management Defaults
  8. · The Settings Drop-Down List
  9. · Choosing from the RGB Working Spaces Drop-Down List
  10. · Color Management Policies
  11. · Conversion Options: Which Engine to Use
  12. · Black Point Compensation
  13. · Assigned Profile
  14. · Color Management Policies in Action
  15. · Converting a Profile Means Changing the Data
  16. · Soft-Proofing, or Seeing Onscreen What an Image Will Look Like When It's Printed

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The Critically Important Color and Gamma Calibration Article - Converting a Profile Means Changing the Data
(Page 15 of 16 )

  1. Press Shift+Ctrl(Command)+S to open the Save As dialog box. Choose the As a Copy option and then click Save. Because converting profiles involves changing the data, this is the right time to make a backup copy of Vision.tif. You or the client may change your mind at some point about the way you want to use this file.

  2. With Vision.tif open in Photoshop's workspace, choose Image, Mode, Convert to Profile from the menu. The Convert to Profile dialog box opens (see Figure 2.11). Position the dialog box so that you can still see most, if not all, of Vision.tif, and make sure the Preview option is checked.

Insider - The Convert to Profile dialog box is divided into three sections. The first lists the profile of the Source Space. This corresponds to the working color space profile. In the middle section, Destination Space, you choose a profile that defines which color space and color mode the CMS will change the data to fit inside. The last section, Conversion Options, should look familiar; it involves options, such as Intent and color management engines, that you learned about earlier in the chapter.

  1. Click the arrow next to the Profile drop-down list. Notice that in addition to the standard RGB color spaces you saw in the Assign Profile dialog box, this list includes profiles not only for RGB but also for other color modes.

  2. Choose sRGB IEC61966-2.1 from the Profile drop-down list. Notice that the image got brighter, not duller as it did in the previous example, because the dialog box opens with a CMYK profile chosen, instead of the current working profile. And CMYK is always duller than RGB, and even sRGB.

  3. While watching to see how the image changes or doesn't change, try each of the four rendering intents. You'll notice that for this image, little if any change occurs in the image preview when you change the rendering intent. For some images there would be noticeable changes.

Figure 2.11
Use the Convert to Profile dialog box to convert from one color profile to another in the same color mode, or to one in an entirely different color mode. This is the preferred way to change from RGB to CMYK.

Insider - Based on the earlier discussion of Intents, Relative Colorimetric is probably the best choice. This is not a photograph, and with the full spectrum gradient at the edges, maintaining the white point, and then using absolute values where possible, this will most likely produce the best conversion of values.

  1. Choose Relative Colorimetric from the Intent drop-down list. To see what will happen if you choose Relative Colorimetric, you can look at the preview if you have that option selected (see Figure 2.12). Leave the Engine option set at Adobe (ACE), leave Use Dither checked and uncheck Use Black Point Compensation. As mentioned in the Color Settings section of the chapter, the rule of thumb is to turn off Black Point Compensation when you're converting from one RGB profile to another.

  2. Click OK. Press Alt(Opt)+Ctrl(Command)+Z three times, pausing between clicks to see what effect the Convert to Profile has on the image colors. The shift in color is particularly noticeable in the greens. This is not surprising because Adobe RGB (1998) has a lot more greens in its color space than does sRGB IEC61966-2.1. By the third Step Backward, the image should be back in Adobe RGB (1998) mode; leave it there and leave the image open in Photoshop's workspace.

Figure 2.12
With the Preview option checked, you can see how different Intent choices change the look of the image.

Tip - Look to the status bar for clues

If you ever become confused as to which profile is currently the assigned profile, look at the bottom of the Photoshop interface (on the status bar). If you don't see a status bar, go to the Window menu and choose the Status Bar option. On this bar, you have access to information (including the current viewing magnification of a document in the lower-left corner). You'll also see a right-facing arrow (on this status bar). Click on the arrow and choose Document Profile from the context menu list, and the status bar will now display the currently assigned profile for the active document.

In fact, knowing that this information is available at your fingertips, you might want to consider choosing the option to "Leave as is (don't color manage)" when opening a document that prompts a Missing Profile dialog box to appear. By choosing not to color manage, you can then see what profile is assigned to the image (simply by observing the status bar). If you want to assign a different profile, you can still do so within the Photoshop interface. This method of waiting to change a color profile gives you more control over the results. Here's why: If you make a profile change when opening the document, there are no previews to see the effects of that change. But once the document is open, you can then access the Assign Profile dialog box within Photoshop, and with the Preview option selected, you can see (for yourself) the effects of any profile changes (as we have demonstrated in the exercises from this chapter).

Seeing how the image changes depending on which profile you assign or convert to might have given you the idea that whenever you want to see how a particular image will look when it's output to the Web or to print you could or should change the image profile. Don't! There is a much easier, safer, and more elegant way to do it. It's called soft-proofing an image. Read on, and you'll find that Adobe has tucked this time-, money-, and fingernail-saving feature in the View menu.

This chapter is from Inside Photoshop CS,  by Gary D. Bouton. (Sams, 2004, ISBN:  0672326442). Check it out at your favorite bookstore today. Buy this book now.

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