ChApter 2. digitAl workFlow
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includes a device independent color space such as CIE LAB, called a profile
connection space. This gives it a device independent color value to use in the
next step.- It looks up the device independent CIE LAB color value in the output
profile and uses the adjustment found there to determine what color value to
send to the output device.
This three-step process, called rendering, converts the color values found in
the source image into the color values needed to obtain accurate colors in the
output. As this process takes place, there may be colors that one device can
reproduce that the other device can’t because they are out-of-gamut. When
this happens the input color value is changed to a color that is in gamut on
the output device. The rules that govern this adjustment when using ICC
profiles are known as rendering intents and there are four of them to choose
from.
- Perceptual is the most commonly used intent in digital photography and
is based on the fact that relative color values are more important to a viewer
than absolute values. This intent adjusts the entire gamut of the image so it
fits the gamut of the destination device. Even colors that were in-gamut are
adjusted so the relationships between colors remain the same and the overall
look of the image is preserved. - Colorimetric comes in two versions, relative and absolute (the difference
is based on whether the white point is adjusted or not). In digital photogra-
phy the relative version is sometimes used and the white point of the source
color space is changed to the paper white of the output device so whites in
the original image remain white in the output. This intent to retain a near
exact relationship between in gamut colors, even if this clips out of gamut
colors. In contrast, perceptual rendering tries to also preserve some relation-
ship between out of gamut colors, even if this results in inaccuracies for in
gamut colors. If you use the colorimetric rendering intent when converting to
a smaller color space you may see banding, posterization and other artifacts
into the image. - Saturation is designed to produce saturated colors without trying to be
accurate. This intent is never used in digital photography but is best when
printing or displaying pie charts and other solid colors found in business
graphics.
ProFileS in PhotoShoP
When an image is opened in Photoshop, if its profile doesn’t match the work-
ing space you are often given choices. They include:- Use the embedded profile (instead of the working space).
- Convert to the working space.
- Discard the embedded profile and don’t color manage.
Instead of choosing a profile blindly, you can select the last choice to discard
the embedded profile. When the image opens, you can then use the Edit >
Assign Profile command to assign other profiles to it to see which has the
best effect on the colors. When you then save the file you can embed the new
profile.
A color management
system uses an input
profile, a profile
correction space and an
output profile to adjust
colors as they are
moved from one device
to another.