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[Thomas Baumann <thomas@xxxxxxxxxxx>]

Thank you for your explanation. I am not quite with you, though. Sure,
there is nothing to weight and mix in the deghosted area with pixels
from only one exposure, but nevertheless brightness and contrast of this
area follow nicely when I increase exposure-mu. Perhaps this adaptation
mechanism at the border ceases to work when the exposure is too far off.
There might even be a built-in limit to prevent side-effects like
increased noise.

Contrary to my former statement, there is a symmetrical effect when
deghosting a bright area with pixels from the darkest exposure. This can
be seen in the new combined testcase tc3:

$ enfuse --saturation-weight=0 --exposure-mu=0.0 -o 161022_tc3_mu00.tif 161022_tc3_70??.tif
$ enfuse --saturation-weight=0 --exposure-mu=0.2 -o 161022_tc3_mu02.tif 161022_tc3_70??.tif
$ enfuse --saturation-weight=0 --exposure-mu=0.5 -o 161022_tc3_mu05.tif 161022_tc3_70??.tif
$ enfuse --saturation-weight=0 --exposure-mu=0.8 -o 161022_tc3_mu08.tif 161022_tc3_70??.tif
$ enfuse --saturation-weight=0 --exposure-mu=1.0 -o 161022_tc3_mu10.tif 161022_tc3_70??.tif

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https://bugs.launchpad.net/bugs/1649122

Title:
  Enfuse brightness mismatch in deghosted area

Status in Enblend:
  Triaged

Bug description:
  Enfuse results in a brightness mismatch of dark deghosted areas when
  exposure-mu is decreased from its default value.

  Program Version:
  - enfuse 4.1.3 (could not compile 4.2)

  Platforms:
  - Debian Jessie
  - OS X 10.11.6 via MacPorts

  
  == Testcase Files ==

  https://www.dropbox.com/sh/8la13xukmfamjk5/AACI6mruatMEsZ27wZgl8ysha?dl=0

  Bracketed exposures:
  161022_tc2_7079.tif - RGBA
  161022_tc2_7081.tif - RGBA
  161022_tc2_7083.tif - RGBA
  161022_tc2_7085.tif - RGBA
  161022_tc2_7086.tif - RGB

  Enfused results:
  161022_mu00.tif - exposure-mu=0.0
  161022_mu02.tif - exposure-mu=0.2
  161022_mu05.tif - exposure-mu=0.5 (default)

  Commands to reproduce:
  $ enfuse --exposure-mu=0.0 -o 161022_mu00.tif 161022_tc2_70??.tif
  $ enfuse --exposure-mu=0.2 -o 161022_mu02.tif 161022_tc2_70??.tif
  $ enfuse --exposure-mu=0.5 -o 161022_mu05.tif 161022_tc2_70??.tif

  
  == Detailed Description ==

  Deghosting;
  All exposures except the lightest one (..7086) share the same alpha channel which masks a dark area in the middle of the image for deghosting of moving leaves. The masking is binary, there are no partially masked pixels.

  When I change the exposure-mu parameter from its default 0.5 to a
  smaller value to darken the image, the deghosted area stays much
  lighter than its surroundings. The problem does not occur when
  deghosting a bright area using pixels from a dark exposure.

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