PDFlib 8 Windows COM/.NET Tutorial

3.5.3 Color Management and ICC Profiles
PDFlib supports several color management concepts including device-independent color,
rendering intents, and ICC profiles.
Cookbook A full code sample can be found in the Cookbook topic color/iccprofile_to_image.
Device-Independent CIE L*a*b* Color. Device-independent color values can be specified
in the CIE 1976 L*a*b* color space by supplying the color space name lab to setcolor( ).
Colors in the L*a*b* color space are specified by a luminance value in the range 0-100,
and two color values in the range -127 to 128. The illuminant used for the lab color space
will be D50 (daylight 5000K, 2˚ observer)
Rendering Intents. Although PDFlib clients can specify device-independent color values,
a particular output device is not necessarily capable of accurately reproducing the
required colors. In this situation some compromises have to be made regarding the
trade-offs in a process called gamut compression, i.e., reducing the range of colors to a
smaller range which can be reproduced by a particular device. The rendering intent can
be used to control this process. Rendering intents can be specified for individual images
by supplying the renderingintent parameter or option to load_image( ). In addition, rendering
intents can be specified for text and vector graphics by supplying the renderingintent
option to create_gstate( ).
ICC profiles. The International Color Consortium (ICC) 1 defined a file format for specifying
color characteristics of input and output devices. These ICC color profiles are considered
an industry standard, and are supported by all major color management system
and application vendors. PDFlib supports color management with ICC profiles in the
following areas:
> Define ICC-based color spaces for text and vector graphics on the page.
> Process ICC profiles embedded in imported image files.
> Apply an ICC profile to an imported image (possibly overriding an ICC profile embedded
in the image).
> Define default color spaces for mapping grayscale, RGB, or CMYK data to ICC-based
color spaces.
> Define a PDF/X or PDF/A output intent by means of an external ICC profile.
Color management does not change the number of components in a color specification
(e.g., from RGB to CMYK).
Note ICC color profiles for common printing conditions are available for download from
www.pdflib.com, as well as links to other freely available ICC profiles.
Searching for ICC profiles. PDFlib will search for ICC profiles according to the following
steps, using the profilename parameter supplied to load_iccprofile( ):
> If profilename=sRGB, PDFlib will use its internal sRGB profile (see below), and terminate
the search.
> Check whether there is a resource named profilename in the ICCProfile resource category.
If so, use its value as file name in the following steps. If there is no such resource,
use profilename as a file name directly.
1. See www.color.org
84 Chapter 3: Creating PDF Documents (Edition for COM, .NET, and REALbasic)