Introduction to PDF Color: Fun with Whitepoint

Introduction to PDF Color: Fun with Whitepoint

I used a lot of Duckies in preparing my Introduction to PDF color presentation. *insert obligatory AHA disclaimer here* My experiments with CalRGB and WhitePoint are largely derivative of my ICC profile experiments, but trying to answer another question:

What the heck is this WhitePoint parameter that’s used for the CalGray, CalRGB and LAB color spaces, and what are valid values for this parameter?

White Point is generally defined as the whitest point of a printed page, just like Black Point is generally defined as the blackest black you can produce with an ink. Though the PDF Reference states:

The WhitePoint and BlackPoint entries in the color space dictionary control the overall effect of the CIE-based gamut mapping function described in Section 6.1, “CIE-Based Color to Device Color.” Typically, the colors specified by WhitePointand BlackPoint are mapped to the nearly lightest and nearly darkest achromatic colors that the output device is capable of rendering in a way that preserves color appearance and visual contrast.
WhitePoint is assumed to represent the diffuse achromatic highlight, not a specular highlight. Specular highlights, achromatic or otherwise, are often reproduced lighter than the diffuse highlight.

I didn’t find that terribly illuminating.  But the all-knowing Wiki offered some intriguing possibilities on this page. If Only There Was Some Way to translate those x10 and y10 values to the CIE X,Y,Z values the PDF Reference requires.

And let’s scrape that table of values for standard illuminant white point values from the wiki page and graft it to the ICC profile comparison discussed earlier

So let’s create a CalRGB colorspaces with these values we’ve scraped.

And the result is:

SwapWhitepoint-out

Learn more about Adobe PDF Library here.

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