Assigning and Converting Color Profiles

If an image has the wrong (or no) embedded color profile, you will have to assign it a profile manually. You can do this in Photoshop using the Edit r Assign Profile command. This determines which color space is used as a reference when interpreting the colors in the image.

If you don't know where the profile-less image comes -

from, you can use the various entries in the Profile dropdown list and the image preview to check which color space looks best before clicking OK to apply it. Here, only the color space information is embedded in the image file - which changes the way the colors in the image are interpreted but does not alter the image data itself.

Assign Profile

Assign Profile: Don't Color Manage This Document O Working RGB: sRGB IEC61966-2.1 © Profile:

Adobe RGB (1398)


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Figure 3-14: The Assign Profile dialog - not to be confused with the Convert to Profile dialog!

It is another, quite serious matter if you convert an image from one color space to another (Edit r Convert to Profile). In this case, the image data is resampled and the new profile is embedded in the image data. If the image doesn't have a profile at all, the resampling takes place from the current working color space (selected in Photoshop preferences) into the new color space.

As well as the target color space, you must select the intent you want to use. This will usually be Relative Colorimetric if you are working with digital photos, as this causes the minimum amount of change in the image colors when the source and target color spaces are relatively similar. If the target color space is smaller than the source space (typical when converting images to CMYK), and if

Figure 3-15: The Convert to Profile dialog. The Intent and various other options must be set when colors are converted for use in a new color space.

your image has highly saturated colors, Perceptual is usually the better choice of intent.

You can also select which engine you want to use for the conversion. We almost always use Adobe (ACE), as it works equally well in Windows or Mac environments.

We recommend that you check the Use Black Point Compensation option, as this automatically adjusts the black point to suit the target color space.

The Use Dither option is only available for 8-bit images and attempts to simulate colors that aren't available in the target color space. Dithering can produce better-looking colors in smaller target color spaces, but it can produce unwanted image artifacts. You will have to experiment and decide from photo to photo whether this option delivers better results.

The Flatten Image to Preserve Appearance option flattens all layers to the background, thus avoiding unpredictable changes to individual layers * See section 714, page 280. that can occur during conversion.*

Work as much as possible in the RGB color space and avoid converting color spaces if you can, as they always reduce image quality. If you convert an image from a large color space to a smaller one and then back, the larger color gamut will not be recreated - in other words, color space conversion is irreversible.

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