Wednesday, October 17, 2012

About Green and other stuff...

Getting there.

As written before, the complications were the Canon files.

At least, that's what I thought.

So I mainly looked for differences between the sensor readings of Leica and Canon.

But despite some differences (Canon seems to favor blue a little bit more than Leica does) it didn't make much sense.

The Leica values and the Canon values were too close to explain the big differences I was seeing.

Then I thought I had the model wrong. Not YUV but maybe YCbCr (in the second one the red and blue are gamma corrected), so I tried that. And that did lead to better results, but was also very photo specific. One photo would need a high setting, another photo a low setting... and in some situations the strength setting would cancel out the gamma setting and the filtering would hardly be noticeable.

Overall it wasn't very satisfying, since I still didn't understand what was going on.

Then, at some point, when I was just lazying around, thinking about this problem, I suddenly realized that in all my tests I had been ignoring the black level, and that the black level might not appreciate that very much.

In my Canon test photos the black level was much higher than in the Leica test photos. It explained the big differences I was seeing.

And indeed: incorporating the original black level in the calculations solved it all.

No more need to gamma correct, it just works on the linear data... for Canon and for Leica and for all kinds of black levels.

I've also been working on a red RGB and blue RGB filter. Quality wise they seem to perform better than the chrominance red and blue filters, but the results are also different (gray-toning wise), so the chrominance filters will stay.

And I still need to figure out if the new red and blue filters require some extra coding on the opposite end of the scale (the white level), since there similar issues might exist.

Anyway, I expect to have these three extra filters finished now pretty soon, in the meantime thinking about orange and yellow...

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