Tuesday, August 30, 2011

The Editor

[Please note that this post is part of a series describing my first wobbly steps into the world of ICC color profiles. The aim is to build an ICC color profile editor from scratch. Seeing how I started this project with no knowledgde whatsoever on the subject, it's wise to realise that some of my findings described in these posts are incorrect. The incorrect conclusions are usually corrected in later posts. For the whole series in one go, click here.]

So, the curve editor I wrote for this color project is approaching its final stages. It still lacks some functionality, but for testing purposes it's quite ok now. Let me show you some examples...

The editor itself is the big black square with the curves, and next to it on the right is the standard proofing picture I use. There will be the option later on to load a random photo, but this thing covers at least the basics: colors and grays.

The first picture is a random profile and you see the TRC curves, all blended together (red, green and blue) in a gamma 2.2 curve.

(for real it looks a bit clearer, the JPG quality and down scaling make the screenshots a bit fuzzy).

Then in the second picture you see I've pulled blue down and the effect is immediately visible in the color transition in the picture on the right (grays turning blue).

With the control point setting on the left I can switch the number of vertical lines in the editor. It means I can set the number of 'points' to pull or push the curve. The more points, the smaller the changes. The nicest curves are actually created with a low number of control points. Gives very smooth results. The highest number of points is 32.

In picture 3 you see the curves out of control in an 8 point setting and the color translation becomes unusable, with the grays especially in the mid tones and highlights turning into everything but gray...

And as you can see, it's actually not that easy to spot that this is a totally whacked color profile if you only focus on the colors. It seems to be the grays that tell the story the quickest. Gray is always a combination of a similar amount of red, green and blue. Any deviation is quickly spotted if you concentrate on the gray scale.

For calibration the editor works basically the same, but the curves have an opposite effect when they move. Pulling blue down decreases blue in the calibration, but with the TRC pulling blue down increases blue through the color translation.

I've still some work left to change the TRCs that are stored as parametric curves (those only have the gamma stored as a number, but not a whole curve) and then I can move on to more daunting parts of a profile: the gamut! (or something :-) )

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