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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 - Choosing from the RGB Working Spaces Drop-Down List
(Page 9 of 16 )

When you click the down arrow to expose the choices offered by the RGB drop-down list, you may find a huge list of profiles from which to choose. The number of profiles in the RGB drop-down list depends on the number of RGB profiles loaded at the system level and whether the Advanced Mode is activated. If Advanced Mode is not activated, the list is rather short. The profiles are grouped into the following categories:

  • Custom. (Available in Advanced Mode only.) At the top of the list is Custom RGB. If you choose this option, you can define your own custom RGB space. Unless you are an expert in color management trying to solve a particular problem, we strongly recommend that you avoid the potential masochism in creating your own RGB workspace. That said, the only reason ordinary Photoshop users might use this feature would be to create a profile for BruceRGB.

  • Load RGB and Save RGB. (Available in Advanced Mode only.) These two commands are found in the second section of the drop-down list. Load RGB enables you to cruise your hard disks for an ICC profile that's not in the system-level Color folder; oddly, this is not an option when Advanced Mode is not checked. Photoshop can convert the monitor setup file (*.ams) into an ICC profile if you save it by using the Save RGB command after you've loaded it with the Load RGB command. Save RGB will save any currently chosen RGB workspace profile to any location on your hard disk, which is handy when you need to share a custom profile with another Photoshop user.

  • Other. This section contains any profile you've created with the Custom command but have not yet saved with the Save RGB command.

  • Monitor RGB. This is a straightforward choice to use Adobe's sRGB space. Although the colors on your screen will look lush on your monitor and on the monitors of others who visit your site, it's a limited color space and not good for much other than Web graphics.

  • Standard Working Spaces. This part of the list contains the profiles that are the best as default working spaces. Unless you are working under unusual conditions, you should choose one of the profiles in this section. The profiles are Adobe RGB (1998), Apple RGB, ColorMatch RGB, and sRGB IEC61966-2.1 (commonly referred to as sRGB).

    • Adobe RGB (1998). A good all-around RGB working space with a color gamut large enough to produce decent RGB or CMYK printed output. This is our recommendation as a default working space.

    • Apple RGB. A good working space if your finished work will be seen only on Macintosh OS monitors, or if you are using older software that is not capable of color management. This working space is used by the Emulate Photoshop 4 preset. I use Apple RGB space on a Windows XP machine occasionally to work between Apple and Windows systems, for comparison's sake.

    • ColorMatch RGB. A working space that corresponds to the color space of the Pressview monitor. A small color space, it is sometimes used for images that will be output to a CMYK commercial printing press. Many prepress experts prefer to use a larger space than this for print work.

    • sRGB IEC61966-2.1. The working color space of choice for the creation of Web graphics. If you think you will use an image on the Web and also in print, choose Adobe RGB (1998) as your working space instead. sRGB is too narrow for print work, even on RGB inkjet printers.


Note - Mac's ColorSync RGB

On the Macintosh, ColorSync RGB is also available as a standard working space. The actual working space used when Macintosh ColorSync is chosen depends on what you've chosen in the Apple ColorSync Control Panel.


  • More RGB Profiles. (Available in Advanced Mode only.) The last section of the list contains all other RGB profiles available in your computer's system-level Color folders. You'll see all kinds of default device profiles for monitors, printers, scanners, and cameras, as well as profiles installed by RGB equipment you own. A few standard working spaces are listed here also: They include NTSC (1953) and PAL/SECAM,SMPTE-C, which refer to TV and video color spaces; CIE RGB and Wide Gamut RGB, which are both very wide, large color spaces that are not recommended unless you are working with files that are 16 bits per channel.

Adobe RGB (1998) is the best overall choice for working with or creating images that will output in a variety of ways. Logos, for example, typically are used in print, on the Web, in videos, and on product packaging. If you want to be able to set and forget your workspace profile, Adobe RGB (1998) is the one to choose because it is the most flexible workspace. If you want to tweak images from the moment the first pixel is laid down, you should choose one of the special-use profiles that will work best for your intended output.


Note - Meet BruceRGB

One other standard RGB space, BruceRGB, is worth mentioning. Bruce Fraser, a prepress guru and writer, felt that Adobe RGB was too large a color space and that ColorMatch was too small for most prepress work. BruceRGB has become one of the accepted standard working spaces in the prepress world. Unfortunately, Adobe doesn't install the BruceRGB profile along with the other standard RGB working spaces. You can use the Custom RGB feature described earlier, however, to create this profile. To obtain the values, you must enter them in the Custom RGB dialog box to create the profile.


Choosing from the CMYK Working Spaces Drop-Down List

The profile you choose in the CMYK drop-down list is the profile that will be applied to new CMYK images you create. You should be aware that what you specify as your default working CMYK space is also the default space when you use the View menu's proofing feature. Unless a custom proofing space is specified, the default CMYK working space is used for the soft-proof view, even when the image being proofed is an RGB image or has a different CMYK working space. The structure of the drop-down list parallels that of the RGB list:

  • Custom. When you click on the CMYK Custom option, you'll see a dialog box that will be familiar if you ever looked at or changed the CMYK settings in Photoshop 5.5. If you need to tweak the settings of an existing profile or create one of your own, this is the place to do it. But if you are trying to re-create a custom setting you created and saved in an earlier version of Photoshop, it's easier to use the Load CMYK and Save CMYK options instead.

  • Load CMYK and Save CMYK. Use these two commands to load new ICC profiles you may have obtained, or to load CMYK Setup files (*.API) or Separation Setup files (*.ASP) you may have created in previous versions of Photoshop. Use Save CMYK to save a loaded ICC profile to disk or to convert and save a CMYK Setup file or Separation Setup file you've loaded to the now-standard ICC profile that Photoshop CS uses.

  • Other. This section contains any profile you've created with the Custom command and have not yet saved with the Save CMYK command.

  • Standard CMYK Work Spaces. This section contains the profiles you'll use most. These standard profiles were designed to describe the colors that can be printed using various kinds of presses and papers under print conditions typical in the U.S., Europe, and Japan. You should choose for your default the profile that matches the CMYK press conditions you most often use. If you are working with files from Photoshop 4 or earlier, or files that will be used in older publishing programs that are not capable of color management, you may prefer to choose a standard profile—the Photoshop 4 Default CMYK or Photoshop 5 Default CMYK profile—from the next section on the list instead. On the Macintosh, ColorSync CMYK is also available as a standard working space. The actual working space used when Macintosh ColorSync is chosen depends on what you've chosen in the Apple ColorSync Control Panel.

Generally, the CMYK ICC profile you use for soft-proofing would be the same one you use for conversion from RGB or LAB to CMYK.

Choosing from the Gray Working Spaces Drop-Down List

By now you've surely (and correctly) guessed that the Gray drop-down is used to specify which profile is used by default with grayscale images. This one has a twist: It has a few custom commands:

  • Custom Dot Gain. (Available in Advanced Mode only.) Choose this command to display the Custom Dot Gain dialog box, where you can enter values or click points and drag on the curve to create a profile that matches the way dot gain occurs at different halftone percentage points when printed. Dot gain is the amount by which a printed halftone dot increases or decreases in size when the ink, dye, toner, or other pigment is applied to the printed surface. To determine how to construct the curve, you should use a densitometer to take readings from a gradient bar that actually used the same inks, media, and output device you will ultimately use. For example, if the densitometer produces a reading of 16% when it reads the 10% portion of the gradient tint bar, you would type 16 in the 10% field of the Custom Dot Gain dialog box. If you do not have access to test prints, ask the folks who run the press which values you should use.

  • Custom Gamma. (Available in Advanced Mode only.) With this command you can create a profile for grayscale images that mimics their display on a monitor that has a custom gamma setting. Gamma determines the contrast of the midtones in an image. If you want to use a profile that reflects the gamma settings for Macintosh and Windows monitors, use either the Gray Gamma 1.8 or 2.2 settings at the bottom of the list.

  • Load Gray and Save Gray. (Available in Advanced Mode only.) Use these commands to load custom gray ICC profiles you may have obtained but that are not installed, or to save a custom setting you've created.

  • Other. This section contains any profile you've created with the Custom command but have not yet saved with the Save Gray command.

  • Standard Gray Working Spaces. The balance of the list contains standard profiles that reflect dot gains of 10, 15, 20, 25, and 30%. Typically, you obtain this sort of information by asking the pressman who is familiar with the (device-dependent) physical printing press. This dialog box section also contains standard profiles called Gray Gamma 1.8 and Gray Gamma 2.2. Gray Gamma 1.8 mimics the default gamma of a Macintosh OS monitor and also corresponds to the default grayscale setting used in Photoshop 4 and earlier versions. Gray Gamma 2.2 corresponds to the default gamma of a Windows OS monitor. Choose the default setting that most closely matches the behavior of your most common grayscale output.

Choosing from the Spot Working Spaces Drop-Down List

The default choice you make in the Spot working spaces drop-down list differs from the others in that it governs the way spot color channels and duotones display. These profiles are the only ones that are not attached to files themselves, as you would embed other types of profiles in saved files. The choices here are identical to those offered in the Gray Working Spaces drop-down, except that Custom Gamma and the two Gray Gamma choices are not available here. You create custom dot gain profiles and choose between standard default profiles based on the same information and concerns you would for dot gain in the Gray Working Spaces. If the system-level Color folder holds custom Grayscale ICC profiles, another section (the custom Grayscale set) will appear after the Standard set.

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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