Photoshop and Color Management - Color Management for Photographers - page 84

The Engine pop-up menu allows users to pick the CMM to be used for
color space conversions. The option called ACE (Adobe Color Engine) is the
CMM that Adobe created and is recommended. See the sidebar, “Black
Point Compensation,” because it is unique to Adobe applications. The
check box Use Dither (8-bit/Channel Images) is used when converting 8-bit
per color images. It allows Photoshop to mix colors in such a way that
aliasing is reduced when conducting color space conversions. Keep this
check box applied to prevent banding in gradients and smoothly shaded
real-world images (skies, subtle shadows, etc.).
Sidebar
Black Point Compensation: Black Point Compensation can be used when making color space
conversions of images using ICC profiles. An example would be converting from RGB to CMYK.
The conversion process using ICC profiles requires a source, where the document is coming
from; and a destination, where the document is going. Because there is no standard specifica-
tion for how ICC profiles map solid black from the source color space to the destination color
space, there are cases where the solid black of an image can produce less than solid black in
the resulting converted image.
To correct these possible problems, Adobe has a switch in the ACE CMM called Black Point
Compensation . Turning this switch on causes ACE to ignore the actual luminance of black in
the source color space. With this switch on, the darkest black in the source space is mapped to
the darkest black in the destination. I recommended that you use Black Point Compensation.
Note that Black Point Compensation is not an option when using the absolute colorimetric
intent. In most cases, the results with this option being utilized will provide a better appearing
preview indicating it should be used for the color space conversion. Black Point Compensation
can also be used for soft-proofing images on-screen and is discussed when configuring Photo-
shop's custom proof setup later in this chapter.
Section 5: Advanced Controls (Visible only when Advanced Mode
Check Box Is Applied)
There are two options controlled by a data entry field and a check box
to turn the features on or off. The Desaturate Monitor Colors by: check box
allows the user to specify how much the preview is desaturated in an
effort to deal with images in a color space whose gamut is larger than
their display. Since some images can contain colors that are outside the
gamut of the display, the idea is to lower the preview saturation so that
these colors can be seen. However, the preview will no longer be an accu-
rate indicator of the final output. This setting is recommend by Adobe
only for advanced users. I suggest ignoring this option unless you have
a compelling reason to work with a very large gamut working space and
don't mind that the preview becomes quite inaccurate.
The Blend RGB Colors Using Gamma is another setting for advanced
users and is a means for overriding the default color blending normally