Although some images may share identical RGB values, their appearance differs because every imaging device responds to color stimuli differently. The first square is from a Flextight 949 scanner, the second is from my monitor, and the third is from a Light-Jet printer. To work efficiently, you need a way to accurately preserve color information from a digital camera or scanner, through editing and correction to a finished print. Color management helps you do just that.
	Here’s an experiment: Download the Colorspaces.zip archive, open the image Colorspaces1.tif, access the Info palette (F8), and move your cursor over the window. The RGB values in the Info palette will read 124, 16, 87. Duplicate the image two times for a total of three images (Image > Duplicate). Leave the first image in its native colorspace of Adobe RGB (1998). With the first duplicate active, choose Image > Mode > Assign Profile, and assign sRGB Profile as the Destination Profile. On the second duplicate, assign ColorMatch RGB as the Destination Profile. Using the Info palette, verify that the RGB values for the three images are identical even though the visual appearance of all the squares is different.
	Close the two duplicates, then duplicate the original image twice more. This time, instead of assigning a new colorspace to the image, convert the color profiles to the new colorspace by choosing Image > Mode > Convert to Profile. For the first duplicate, convert to the sRGB Profile. Under Conversion Options choose Relative Colorimetric as the Intent, then check Use Black Point Compensation and Use Dither, and click OK. Convert the second duplicate to Color- Match RGB using the same settings for the Conversion Options as used earlier in this step. If you check in the Info palette, you’ll see the RGB values for the first duplicate change to 144, 16, 89, and the second duplicate’s RGB values change to 119, 10, 73, yet their color appearances stay the same (Note: You might have some value variations due to your own internal settings.) The color behavior of a device such as a printer or scanner is measured and stored in an ICC profile. At every stage in the imaging workflow, the profile associated with an image tells Photoshop what colors should look like. When an image moves from one portion of the workflow to another, say from RGB editing to CMYK printing, the image is converted from the Source Space (RGB editing space) to the Destination Space (CMYK printing) using the Convert to Profile command. This accurately preserves the image’s color appearance at all stages of the workflow.
	It is recommended for RGB workflows to convert images from an input space (digital camera or scanner) to an editing space such as Adobe RGB (1998), sRGB, or ColorMatch RGB. These mathematically generated colorspaces are optimal for tone and color correction, archiving, and storage. The editing space you choose is dictated by your workflow, and the devices you commonly use for output. Adobe RGB (1998), for example, is used for photography applications such as advertising and fine art. The profile sRGB is the best choice for images destined for the Web and portrait photography. Both colorspaces are shown in the ColorThink diagram. The center axis represents the grayscale from black to white. The further from the center a color lies, the more saturated it is. Adobe RGB (1998) is represented by the wireframe, and sRGB is the solid. Notice the larger color gamut of Adobe RGB (1998) particularly in the reds and greens. CMYK-based workflows are generally tied to a specific printing press or press condition, e.g., a sheetfed press printing on coated paper. Users should work in the colorspace that best describes the file’s output destination. Often, when images are converted from one colorspace to another, some colors can’t be faithfully reproduced because they lie outside the destination’s color gamut. Photoshop’s rendering Intent gives us the option of deciding how gamut colors should be converted to the new colorspace. Of the four rendering intents used in Photoshop, only two are used commonly, Relative Colorimetric and Perceptual.
	Open Colorspaces2.tif Choose the Convert to Profile command and make sure Preview is checked. Choose U.S. Sheetfed Coated v2 as the Destination Space and move down in the dialog box to Conversion Options. When the Relative Colorimetric rendering Intent is chosen, the appearance of the two colors is unchanged. If Perceptual rendering Intent is chosen, both colors become slightly darker. Relative Colorimetric rendering Intent is used for the majority of images where overall color accuracy is most important.
	Now, open the file Colorspaces3.tif. Again, open the Convert to Profile dialog box and choose U.S. Sheetfed Coated v2 as the Destination Space. Notice that when Relative Colorimetric is chosen as the Intent, the two red squares are converted to the same color. When the Perceptual rendering Intent is used, the differences between the two squares are preserved, although the color accuracy of both squares is compromised. The Perceptual rendering Intent is used for image conversions where saturated image detail is more important than color accuracy.

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Jay Kinghorn is a digital workflow consultant based in Boulder, Colorado.