Graphics Programs Reference
In-Depth Information
one color space but not available in another color space are called out-of-
gamut colors . Colors in the original (source) color space need to be mapped
to colors that exist within the gamut of the new (destination) color space.
There are two basic techniques for mapping out-of-gamut colors. One
technique is to take all the colors that are out-of-gamut and map them
to the closest colors that are within color gamut of the destination (see
Fig. 1-11). We call this technique gamut clipping . The second technique is
to compress the range of color into the gamut of the destination. It is
important to note that when using this method, some colors that were
perfectly matched between the two devices will actually change. We call
this method gamut compression .
The ICC system provides different methods of gamut mapping and
calls these rendering intents . When you perform ICC color transformations
within an application, you will need to choose a rendering intent. The
rendering intents were created for different situations. The names of the
renderings are colorimetric , saturation , and perceptual .
The colorimetric method is a form of gamut clipping. The saturation
intent is also a form of gamut clipping, but attempts to preserve the sat-
uration of colors over lightness. The perceptual method is a form of gamut
compression. When using the perceptual method, visual detail and
luminance are preserved over hue and saturation.
Let's take a closer look at each rendering intent and see how they
operate.
The perceptual rendering intent transforms the colors so that the
image in the destination space is perceived in the same way as the orig-
inal. The conversions are weighted to deal with luminance over satura-
Fig. 1-11 This illustration
shows the primary
differences in gamut
compression and gamut
clipping using rendering
intents. (Illustration by Karl
Lang)
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