Photoshop Color Settings

Tells Photoshop how to process an image's colors

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Working Space

Working space is how Photoshop refers to its default color spaces.  We tell Photoshop what to use as the default color spaces in its Color Settings dialog box as seen in Figure 1.  This dialog box is accessed by clicking Edit > Color Space.  We can set up to four default color spaces.  One for RGB, one for CMYK, one for Grayscale and one for Spot.  Whether or not Photoshop automatically assigns the default color space to an image is based on how we set up the Color Management Policies in the Color Settings dialog box.
 

Color Management Policies

The Photoshop Color Management Policies tell Photoshop whether or not to use the color profile embedded in an image and what to do if the embedded profile is different from the working space profile.  It can also forewarn us if an image does not have an embedded profile.
 

Converting Color Spaces

If we need to change an image's color space, we convert it from one color space to another using Photoshop's Image > Mode > Convert to Profile and then save the image so the new profile gets embedded with the image.

The fact that two color spaces are involved means there are two color gamut's involved.  This means one set of predefined colors is being converted to another.  By definition, no two color gamut's are the same.  (If they were, why bother having a second one?)  Therefore, in any two different color spaces, one will have colors the other doesn't.  If a color exists in the original, or source, color space but not the destination color space, then Photoshop (or any other image editing software) needs to know how to convert the mismatched color.  We set these options in the Conversion Options section of Photoshop's Color Settings dialog box.
 

Conversion Options: Engine

The Engine option tells Photoshop what software will handle the conversion.  I leave mine set to Adobe.
 

Conversion Options: Rendering Intent

Colors in the source color space that are not in the destination color space are known as out of gamut colors.  The Rendering Intent option tells the color conversion engine how to handle out of gamut colors.  There are four options.

• Perceptual.  If out of gamut colors are encountered, then the Perceptual intent will shift both in gamut and out of gamut colors so as best to preserve the visual relationship between the colors while remapping out of gamut colors to a color that is in gamut in the destination color space. 
• Saturation.  Converts the image's colors to highly saturated in gamut colors in the destination color space.  I do not recommend the Saturation intent for photographers.  It is more appropriate in graphics where color accuracy is not critical.
• Relative Colorimetric.  For in gamut colors, maps color to color between source and destination color spaces.  For out of gamut colors, remaps the color to the closest in gamut color.  Maps source white to destination white.
• Absolute Colorimetric.  For in gamut colors, maps color to color between source and destination color spaces.  For out of gamut colors, remaps the color to the closest in gamut color.  Does not remap source white to destination white but rather converts white as a color, so whites may look different once converted to the destination color space.

 

Most photographers use either the Relative Colorimetric or Perceptual intent.  Perceptual attempts to maintain color relationships over accuracy while Relative Colorimetric strives to maintain color accuracy.
 

Conversion Options: Black Point Compensation

Tells the conversion engine whether or not to adjust for any differences in black between the source and destination color spaces.  If turned on, the full range of the source and destination color spaces are used during the conversion.  If turned off, black and other dark colors can appear muddy.  I cannot think of a reason as to why this option should be turned off.
 

Conversion Options: Dithering

When processing out of gamut colors in an 8-bit per channel image, it tells the engine to combine colors in the destination color space in such a way as to best represent the out of gamut color.  Can help minimize posterization but can also lead to larger file sizes.  The Channels and Bit Depth page explains bit depth.