Checking the Advanced Mode check box at the top of the Color Settings dialog box displays two sets of additional settings shown at the bottom of Figure 15.3, Conversion Options and Advanced Controls.
In the Conversion Options area, the Engine setting enables you to set or change the color management engine that is used for color conversions (see Figure 15.7). Depending on the options available on your computer, those options range from a selection of two to six or more.
Figure 15.7: The Engine conversion options
Adobe has its own color management engine (in the parlance of the industry this is called a CMM, or color management method): Adobe Color Engine (ACE). Other CMMs you might encounter include Apple ColorSync, Heidelberg, Kodak, Imation, or Agfa.
Which engine should you choose? Each company suggests that its CMM uses a superior method of polynomial voodoo to convert color. Adobe similarly claims that theirs is
In reality (and with apologies to the various authors of these CMMs), the net effect of a color management engine is
Figure 15.8: The Intent conversion options
Perceptual is a rendering intent designed to make photos of generalized subjects look good when converted to a new color space. The Perceptual rendering intent uses a method of remapping colors that
Saturation is for business graphics and illustrations made with solid colors. Of the four intents, it is the easiest to understand and the
If you convert RGB images from EPS illustration programs such as Adobe Illustrator, the Saturation rendering intent will result in a better-looking image after conversion than the other intents. Saturation is best used when converting graphs,
Relative Colorimetric rendering is a method in which color precision is preferred over saturation, resulting in a more accurate conversion of colors into a new color space. Adobe s experts and many prepress professionals recommend that Relative Colorimetric rendering be used for most color conversions. One of the key
Relative Colorimetric should always be used with Black Point Compensation. Otherwise, shadow detail will plug up, because the black points in the conversion might not be mapped correctly.
This rendering intent is much like the Relative Colorimetric intent, except that it
There are two additional settings in the Color Settings dialog box under Conversion Options: Use Black Point Compensation and Use Dither (8-Bit/Channel Images). Black Point Compensation is generally set, because it maintains saturation of solid black in conversions that would normally
An example of this can be seen when converting RGB images to CMYK for print. If you leave this box unchecked and make a conversion (Image
CMYK), the darkest blacks will often be remapped to the
See the sidebar on Dot Gain later in this chapter
The Use Dither check box causes 8-bit images to be dithered when converted to 8-bit images of another color mode. Dithering is a method of alternating tonal values in tiny steps to smooth out tonal shifts. Checking this setting will result in smoother gradations in the converted file.
The settings Desaturate Monitor Colors By and Blend RGB Colors Using Gamma, though recommended for advanced users only, can improve the accuracy of the preview of images on your display.
The Desaturate Monitor Colors By option instructs Photoshop to desaturate colors by a specified amount when displayed on-screen. This option can be helpful when attempting to view the full range of colors in images with color gamuts larger than that of your display.
An example of this might be viewing on any display an image whose color working space is Wide Gamut RGB. Because the gamut in Wide Gamut is larger than any production display, this function will simulate the
The Blend RGB Colors Using Gamma setting controls the blending of RGB colors on-screen. When the option is selected, RGB colors are blended by using a selected curve. The range of values available here is between 1.0, which is linear (it has no effect), and 2.2, which creates slightly higher-contrast edge transitions. This option will also affect the blending of tones too (different values than in a gamma compensated edit), as in overlapping content in two
When the option is not selected, RGB colors are blended in the document s color space, matching the color display behavior of other applications.