On 07/20/2014 10:43 AM, Pascal Obry wrote:
> Ok, anyway for now I have output the basecurve from dt-curve-tool and
> will be using this.
Hi the list,
1) Why aren't toncurves showing up when adding the entry to
presets_from_basecurve ?
Roman did remove the lines injecting the preset in the DB because a
warning would prevent compilation of DT if the basecurve array was empty
[1]. This was totally justified because of the warning treated as error
policy in DT.
2) Why is the preset array called xxx_from_basecurve ?
Because at first dt-curve-tool was simply call basecurve. I'll submit a
PR for changing the name of the array.
3) Why should you disable basecurve when using the computed tonecurve ?
I added support for tonecurve because I was totally unsatisfied by the
current basecurve approach which is plainly wrong with regard to
expected colorimetric results[2]. Hence the exclusive use.
I knew DT devs were going to have a meeting at LGM and would discuss
this matter, and probably draw a plan of actions wrt a late tonecurve,
as reminded by Roman.
I just wanted to experimentally prove that a late real tonecurve would
greatlly improve my photo colors, and help some modules do a better work
with linear data as input. I could confirm on my side both improvements,
but I was still unsatisfied of color saturation with the single
tonecurve applied. Colors were lacking some pop. The thing is tonecurve
is only computed for the L* channel, and to make sure color rendering is
JPEG alike, we should take care to compute a* and b* curves, but the
experimental code that is part of the tool shows we don't compute good
curves for these channels.
Hope this explaination helps to put in perpective all the weirdness.
[1] 34e1aefff8bfdf683d2f27a340ceb60ef6c52333
[2] First, basecurve is applied too early in the processing pipe, thus
forcing all modules to work on non linear data wheras their design may
assume linear data input.
Second, basecurve applies a single curve to all RGB channels
independently leading to very wrong colors in certain circumstances (in
my D7000 usacase, all reds/oranges were simply oversaturated). This
approach is way too simplistic, to be correct color wise
--
Edouard Gomez
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