Steve on Image Processing and MATLAB

Concepts, algorithms & MATLAB

B = “Profile Connection Space”

Posted by Steve Eddins,

A couple of weeks ago I asked if anyone could guess what this "equation" means on my office whiteboard:

B=PCS

It's related to the color management approach standardized by the International Color Consortium (ICC). In this approach, each input device (a camera, for example) or output device (such as a printer) has an associated color profile. The color profile contains a numeric "recipe" (multiple recipes, actually) for converting colors between the device's own color space and one of two standard colorimetric spaces: XYZ and L*a*b*. The standard space is called the profile connection space, or PCS.

The idea is to allow color management systems to transform colors appropriately as they move from an input device to a computer display, and then to an output device. All color space transformations in the pipeline work by "connecting" through one of the two standard profile connection spaces.

ICC profiles contain transformation recipes that go both ways: from the device to the PCS, and from the PCS to the device. The lookup tables, curves, and matrices that make up the recipes are stored in tags in the profile. These tags have names like AToB and BToA.

Which finally brings us to the answer to my whiteboard mystery: I have a lousy memory! I could never remember whether "A" referred to the device space, or to the profile connection space. I was always having to look it up in the spec. One day I got tired of this and wrote "B = PCS" on my whiteboard.

Maybe I'll leave it there forever.

Happy New Year, everyone!

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