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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).

Author Info:
By: Sams Publishing
Rating: 4 stars4 stars4 stars4 stars4 stars / 60
December 15, 2004
TABLE OF CONTENTS:
  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 - Color Management Policies
(Page 10 of 16 )

The default working spaces profiles you just went through apply primarily to newly created files. But what happens when you open a file that doesn't have a color management profile attached to it, or that has a different working space profile attached to it than the default profile you've selected? Similarly, what happens when you cut from and paste into images that have different working spaces? The Color Management Policies section in the Color Settings dialog box (see item 3 in Figure 2.7) takes care of situations in which profiles are mismatched. Adobe calls the actions taken by Photoshop to reconcile color mismatches and missing profiles the Color Management Policies.

Each of the three drop-down lists—RGB, CMYK, and Gray—offers the same three Color Management Policy options:

  • Off. This setting doesn't exactly mean no color management at all. It means that an ICC working space will not be assigned to newly created files. This is not to say that the working spaces you have designated are not affecting the soft- proofing capabilities while working on a newly created file in Photoshop. Very large gamut RGB working spaces usually create printed output that is prone to excessive clipping, so a choice here other than Off might be the solution when you aren't happy with the output.

Off also means that profiles attached to documents that are opened will be ignored, and they will be discarded if they do not match the default working space. On the other hand, if the profile of the opened document matches the current default profile, the profile will be preserved.

And Off means that when part or all of an image is pasted into another image, the colors will be added based on their absolute numeric value.


Note - Perception versus numerical value in color conversion

When the numerical value of a color takes precedence in determining how colors are translated from one color space to another, the perceived color often changes, and many observers would not think it a faithful translation. The reason is that the perceived color of inks and dyes is greatly affected by the surface to which they are applied. For example, when a numerically specified color (RGB 97, 176, 224) is applied to newsprint, it appears darker and duller than the same color printed on glossy coated cover stock.

When the perceived appearance takes precedence over the numerical value of a color, the goal is to create a color that appears to be the same on newsprint as on cover stock, even though the actual ink or combination of inks used is wildly different. Maintaining perceptual color fidelity is very important when you are working with corporate colors or most photographic material.


  • Preserve Embedded Profiles. This Color Management Policy means that profiles attached to open documents are used and preserved. When material from one file is copied into another and the working space profiles of the two do not match, this policy attempts to maintain perceptual color values when the receiving image is an RGB or grayscale image, and will use absolute numeric color values when the receiving image is a CMYK image.

  • Convert to Working. When this policy is in effect, the default behavior is to convert all opened images to the current working color space regardless of whether they have a profile attached. Additionally, when image data is copied from one file into another, the appearance of the color always takes precedence, regardless of the color mode of either image.

We recommend that you use the Preserve Embedded Profiles Color Management Policy for all three color modes. You can always change the profile that is attached to an image, but we believe that is a decision you should make consciously and not have happen on a default basis.

Second Guessing Default Color Management Policies

The default policies are useful but they are not always what you really want to have happen. For this reason, Adobe has provided you with the option of asking Photoshop to notify you whenever a mismatch occurs between image profiles when documents are opened or created, and when you open an image that doesn't have a profile. We recommend that you always keep the Profile Mismatches and Missing Profiles options checked so that you are able to make these critical color decisions.

Having Photoshop notify you of mismatches or missing profiles when you open a document is a good idea if your workflow has only a few workstations and the artist is trained to make such choices. In a high-volume workflow with many workstations, however, such on-the-spot decision making can really slow things down.

Advanced Color Settings Options

We've now covered all the Color Settings options that Adobe thinks most people need to make. But other options are available in the Color Settings dialog box. If the Advanced Mode option in the upper-left corner of the dialog box is checked, the dialog box expands to reveal additional important color management settings. Even if you don't want to change these default settings, you should read on because the choices offered in the section on Conversion Intents are those you are asked to make when you convert an image's profile, when you choose a custom soft-proofing profile, and when you assign a print profile.

Check the Advanced Mode option in the Color Settings dialog box if it is not already checked, and then let's move on to the next section.

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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