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Finetuning capture sharpen #19245

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Finetuning capture sharpen #19245

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  1. For modern 14bit raws or low iso images the default of 0.4 for the variance threshold was definitely too high as only the "edges" were corrected and contrasty darker parts of the image were left out from CS correction. We now check for sensor precision and exif ISO and lower the threshold. There is no precise math behind the threshold lowering but just testing a huge amount of images to give a better default as a starting point.
  2. The control name of "edge sensitivity" has been changed to "contrast sensitivity" as this is not about edge detection but local variance.
  3. The radius correction failed in some images as the upper limit missed green channel clipping.
  4. There are images with a correctly calculated radius of > 1.0 so let's use that.

While being here and checking image.c code some constify and simplifications done there.

@jenshannoschwalm jenshannoschwalm added this to the 5.4 milestone Aug 24, 2025
@jenshannoschwalm jenshannoschwalm added feature: enhancement current features to improve scope: image processing correcting pixels scope: codebase making darktable source code easier to manage labels Aug 24, 2025
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See #19231 #18909

@jenshannoschwalm
Finetuning capture sharpen
2efcc41 
1. For modern 14bit raws or low iso images the default of 0.4 for the variance threshold
   was definitely too high as only the "edges" were corrected and contrasty darker parts of
   the image were left out from CS correction.
   We now check for sensor precision and exif ISO and lower the threshold.
   There is no precise math behind the threshold lowering but just testing a huge amount of
   images to give a better default as a starting point.
2. The control name of "edge sensitivity" has been changed to "contrast sensitivity" as this
   is not about edge detection but local variance.
3. The radius correction failed in some images as the upper limit missed green channel clipping.
4. There are images with a correctly calculated radius of > 1.0 so let's use that.
5. A minor tooltip fix

While being here and checking image.c code some constify and simplifications done there.
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feature: enhancement current features to improve scope: codebase making darktable source code easier to manage scope: image processing correcting pixels
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