Epson Color Managed Workflow Manual do Utilizador descarregar pdf (Página 43)

Color management

Adobe Photoshop CS4 for Photographers

This chapter on Digital Capture is provided free with the Adobe Photoshop CS4 for Photographers book. Not for distribution or resale.

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 43). 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 42) 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.

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 or Perceptual CMM and the target

CMYK output is a newspaper color supplement printed

on uncoated paper. If you use the Absolute Colorimetric

rendering intent to convert these ‘targeted’ CMYK colors

to the color space of the prooﬁng device, the proof printer

can reproduce a simulation of what the printed output on

that stock will look like. Note that when you select the

Proof option in the Photoshop print dialog, the Absolute

Colorimetric rendering is applied automatically to produce

a simulated proof print.

Figure 42

You can also change the rendering

intent in the Custom Proof dialog. This allows

you to preview a simulated conversion without

actually converting the RGB data.

Figure 41

The default rendering intent setting

can be overridden when using the Convert to

Prole command.

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