darktable 4.0 default "highlight reconstruction" RAF problem

Started 2 months ago | Questions thread
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FujiShooterCY Regular Member • Posts: 441
darktable 4.0 default "highlight reconstruction" RAF problem


I just upgraded my good old darktable 3.old to 4.0 on Linux and the shiny new highlight reconstruction module immediately threw an unexpected problem at me. Description:

  • clean darktable 4.0 fresh install,
  • stock out of the box default settings, nothing was altered, module order is "v3.0 RAW" as by default,
  • a correctly exposed RAF file with some tiny spots of overexposure on the clouds, white fabrics and sun glares (the "raw overexposure" indicator shows just a few red dots in each, nothing serious - even "clipping indicator" is silent, no clipping detected) is being opened.

In darkroom, these (supposedly) overexposed areas are covered by flat solid patches of a faded bluish color. No, this is not a neutral grey. After some research, it turned to be a problem with the "highlight reconstruction" module painting highlights this ugly way - instead of a neutral white.

Some fiddling with it revealed that

  1. yes, the "show mask" confirms overexposed areas locations,
  2. the "reconstruct in LCh" method only makes the flattened patches bigger in size,
  3. the "reconstruct color" method removes the flat ugly patches, but loosely injects the areas with magenta pixels instead; but Ok - at least no solid patches here,
  4. the "guided laplacians" method is not available (non-applicable?) with X-Trans RAF.

More experimentation with "clip highlights" method and the "clipping threshold" slider (the one equipped with the warning "you shouldn't ever need to touch this", ha-ha) revealed, that moving the slider all the way right (to 2.000) retains solid colored patches but changes their color to magenta.

Moving the slider the left direction from the default value of 1.000, predictably increases the size of the areas covered with that solid faded bluish flat color, and adds some burnout to the surrounding areas, too.

So, my idea of getting rid of the patches just with the slider, immediately failed miserably.

darktable applied the exposure correction +0.5 EV on import by default. I tried decreasing it, the histogram obediently moved to the left and ceased to touch the rightside clipping border, but the colored patched did not change.

My question is: how do I make my (slightly) overexposed spots at least neutral white? And, if possible, how to make all available highlight reconstruction methods equally non-destructive with regard to colors.

Right now I need the urgent solution and a few RAF frames only, so the retouch module will save my life this time, but for future I'd prefer some more robust and unified solution.

Please help me solving this puzzle! Thanks in advance. Regards, Andreas

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