Le 04/02/2017 à 04:03, Anton Aylward a écrit :
I have a picture of a white barrel cactus (Cleistocactus icosagonus) which was
taken in strong light, bringing out the white 'leafs'. The illumination is
along one edge, rather like a crescent moon. The crescent is overblown whenever
I convert to JPEG, and I can't figure out how to manipulate it down without the
rest of the image being darkened or distorted.
Other than ending up dealing with layers in GIMP, or somehow masking the
crescent, which, because of the spiky leaves might be awkward, what can I do
about this? I there some way to 'flatten' the top end of the white alone?
I know some controls have sliders, but, for example, keeping the R&G&B all
aligned is difficult. Is there a way to do numeric input or lock sliders
together?
Or am I just approaching this the wrong way?
Hello.
This is a case of overexposure in strong light, which is a specific case
of high dynamic range situation.
Can you share the RAW file ? I'm curious about the situation and would
like to experiment.
It would allow to confirm that something can be recovered indeed. Else
the following will not be of any help.
No one has mentioned global tonemapping, which is a tool intended for
dynamic range issues.
It may be good here in spite of caveats :
* You seem to want the rest of the image unaffected (which is virtually
never actually /strictly/ desired, for it would look unnatural anyway).
* Drago operator feels like a hack when you read the research paper
https://scholar.google.fr/scholar?cluster=11303574887036255127&hl=fr&as_sdt=0,5&as_vis=1
* Drago operator takes some practice to get something good, and has some
surprising properties. For example, changing the (upstream of the
filter) exposure settings actually changes resulting color rendering.
It's easy to wreck the picture by fiddling blindly with the settings.
That said, it might be useful in this case.
* (suggestion) Take snapshot (left column) to allow left/right
before/after comparison at any time.
* In most cases it makes sense to disable base curve when using global
tonemapping (because it is somehow similar to a basecurve in itself).
* Enable global tonemapping which defaults to drago.
* Because supposedly the picture is not that high dynamic range and you
don't have much dark details to recover, in tonemap module possibly
adjust bias, towards 1 for a weaker effect/more natural rendering.
* Then focus on color: to get the "warmness/sunbathing feel" right /
natural, adjust upstream exposure. Easiest is to use mouse wheel on top
right histogram (on center or right of it, not left part of histogram
which changes black level).
* If resulting picture is too dark or bright, in tonemap module adjust
"target" parameter in small steps.
Hope this helps.
--
Stéphane Gourichon
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