Adobe Photoshop CS5 for Photographers - Martin Evening [290]
Saturation (Graphics)
The Saturation rendering intent preserves the saturation of the out-of-gamut colors at the expense of hue and lightness. Saturation rendering preserves the saturation of colors making them appear as vivid as possible after the conversion. This rendering intent is best suited to the conversion of business graphic presentations where retaining bright bold colors is of prime importance.
Relative Colorimetric
Relative Colorimetric is the default rendering intent utilized in the Photoshop color settings. Relative Colorimetric rendering maps the colors that are out of gamut in the source color space (relative to the target space) to the nearest ‘in-gamut’ equivalent in the target space. When doing an RGB to CMYK conversion, an out-of-gamut blue will be rendered the same CMYK value as a ‘just-in-gamut’ blue and out-of-gamut RGB colors are therefore clipped (see the example over the page in Figure 12.41). This can be a problem when attempting to convert the more extreme out-of-gamut RGB colors to CMYK color, but if you are using View Proof Setup Custom (Figure 12.40) to call up the Customize Proof Condition dialog you can check to see if this potential gamut clipping will cause the loss of any important image detail when converting to CMYK with a Relative Colorimetric conversion.
Figure 12.41 To illustrate how the rendering intent can influence the outcome of a color mode or profile conversion I used Chromix ColorThink 2.1.2 to help me create the diagrams shown on these two pages. The above diagram shows the Adobe RGB color space overlaying a US Sheetfed Coated CMYK color space. As you can see, Adobe RGB is able to contain all the colors that may be squeezed into this smaller CMYK space. The photograph opposite has been plotted on this diagram so that the dots represent the distribution of RGB image colors within the Adobe RGB space. When the colors in this image scene are converted to CMYK, the rendering intent determines how the RGB colors that are outside the gamut limits of the CMYK space are assigned a new color value. If you look now at the two diagrams on the opposite page you will notice the subtle differences between a relative colorimetric and a perceptual rendering (I have highlighted a single blue color in each to point out these differences). The upper example shows a Relative Colorimetric rendering, where you will notice that the out-ofgamut blue colors are all rendered to the nearest in-gamut CMYK equivalent. Compare this with the perceptually rendered diagram below and you will see that these same colors are squeezed in further. This rendering method preserves the relationship between the out-of-gamut colors but at the expense of sometimes (not always) producing a less vibrant separation.
Absolute Colorimetric
Absolute Colorimetric maps in-gamut colors exactly from one space to another with no adjustment made to the white and black points. This rendering intent can be used when you convert specific ‘signature colors’ and need to preserve the exact hue, saturation and brightness (such as the colors in a commercial logo design). This rendering intent is seemingly more relevant to the working needs of designers than photographers. However, you can use the Absolute Colorimetric rendering intent as a means of simulating a target CMYK output on a proofing device. Let's say you make a conversion from RGB to CMYK using either the Relative Colorimetric