Severe contrast enhancements: on 45% rule — and cats

Started Jun 28, 2013 | Discussions thread
ilza
Forum MemberPosts: 82
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Re: LAB mode does not preserve the colours
In reply to knickerhawk, Jul 10, 2013

It seems like kind of an odd argument that adjusting L in LAB "does not preserve the colors". By definition it does.

You speak as a humanities guy lured by the magic of formulae. As opposed to that, in exact sciences we treat formulae as just “an acceptable approximation to reality”; and the reality in the frame of this discussion is the human perception of colors.  AFAIU, we know close to zilch about this topic. (BTW, I started this discussion as a way to advancing this knowledge a teeny-weeny step.)

So it makes perfect sense to discuss color shifts (i.e., perceived color shifts) after adjusting L in the LAB color space.

Of course, the notion of “acceptable approximation” depends on context.  I trust the designers of XYZ and LAB that their mappings as good as it gets — but only in context of considering swatches of colors, not colors inside a real photo image. And when one discusses “contrast manipulation”, one is definitely out of context of color swatches, right?

See the OP: the tonal mapping people know it for a long time that when you change the contrast in the “brightness” channel, it is not enough to just naively preserve the original chromaticity (which would be fine in context of swatches!).  So considering color of swatches is just the first step. What I proposed in the OP is one such way to treat the next step after swatches.

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