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Bug #9024

chromatic aberation correction produces artifacts

Added by Immanuel - almost 7 years ago.

Status:
Triaged
Priority:
Low
Assignee:
-
Category:
-
Target version:
Start date:
10/27/2012
Due date:
% Done:

20%

Estimated time:
Affected Version:
1.0.4
System:
bitness:
64-bit
hardware architecture:
amd64/x86

Description

enabling automatic chromatic aberation correction produces artefacts. The display, as well as the export (attached) is affected.

IMG_7444-01.jpg (6.97 MB) IMG_7444-01.jpg Output created by Darktable Immanuel -, 10/27/2012 06:16 PM
IMG_7444-01-HSV-SATURATION_CHANNEL.jpg (819 KB) IMG_7444-01-HSV-SATURATION_CHANNEL.jpg Saturation Channel after HSV-Decompose Immanuel -, 10/27/2012 06:16 PM
difference_plot.jpg (9.93 MB) difference_plot.jpg difference between export with and without automatic CA Immanuel -, 10/30/2012 05:39 AM
IMG_7444_without_CA.jpg (415 KB) IMG_7444_without_CA.jpg scaled image without CA correction Immanuel -, 10/31/2012 06:07 AM
IMG_7444_with_CA.jpg (402 KB) IMG_7444_with_CA.jpg scaled image with CA correction Immanuel -, 10/31/2012 06:07 AM
IMG_7444_with_CA.jpg (402 KB) IMG_7444_with_CA.jpg gimp file directly compares the effect of CA correction Immanuel -, 10/31/2012 06:07 AM
IMG_7444-HSV.xcf (2.08 MB) IMG_7444-HSV.xcf gimp file with decomposed image (HSV) Immanuel -, 10/31/2012 06:07 AM
IMG_7444.xcf (6.31 MB) IMG_7444.xcf gimp file directly compares the effect of CA correction Immanuel -, 10/31/2012 06:08 AM

Related issues

Related to darktable - Bug #8923: chromatic abberations correction module breaks display of jpegsFixed09/09/2012

Related to darktable - Bug #8746: Chromatic Aberrations does not remove all distortionsTriaged06/04/2012

Related to darktable - Bug #8745: Chromatic Aberrations module causes saturation shiftTriaged06/04/2012

Related to darktable - Bug #8318: Chromatic abberations works randomly for displayTriaged

Has duplicate darktable - Feature #10020: Chromatic aberration improvementNew07/22/2014

History

#1 Updated by Immanuel - almost 7 years ago

This happens on all my PCs with dt installations. Even on DreamStudio live distro.
Just enabling automatic CA correction reveals the problem.

I can provide the *.CR2 file (EOS 550D) if necessary. But I can't attach it here, due to size limit (10MB).

#2 Updated by Immanuel - almost 7 years ago

added difference plot (gimp grain extract) from image with and without automatic CA.

#3 Updated by Torsten Bronger almost 7 years ago

I'm not a developer, so just out of curiosity: Is IMG_7444-01.jpg supposed to have the artifacts, too? Because I cannot see anything bad in the picture except for uniform noise.

#4 Updated by Immanuel - almost 7 years ago

Of course, IMG_7444-01.jpg has those slight aritfacts too. I can see them clearly on my screen. Maybe it depends, how the display is calibrated ...
To make the issue more visible, one can try contrast enhancement (c2g in Gimp) or just decompose it to HSV channels. The artifacts are most clear in the saturation channel.
What I also did, is comparing the image with and without CA. Switching between those two images makes it easier to find the artifacts. See the new attachments.

#6 Updated by Ulrich Pegelow almost 7 years ago

  • % Done changed from 0 to 20
  • Target version set to Future
  • Status changed from New to Triaged

I think these artifacts are not too surprising. The underlying algorithm tries to auto-detect color shifts which are typical of chromatic aberrations
and then optimize them away. Seems like this is done in form of rectangular patches which explains why the effect is not homogeneous.

Of course the algorithm can not really know what is a CA and what is not. In your example image I don't see clear indications of CA's at all, not even
at the rim of the white canvas. So you pay the price of an auto-correction in a case where it does not fit.

Maybe in future we will come up with a better algorithm. The current one was taken from project Rawtherapee and anyhow deserves some love. Not a short term
topic, though.

#7 Updated by Roman Lebedev over 5 years ago

  • Related to Bug #8923: chromatic abberations correction module breaks display of jpegs added

#8 Updated by Roman Lebedev over 5 years ago

  • Related to Bug #8746: Chromatic Aberrations does not remove all distortions added

#9 Updated by Roman Lebedev over 5 years ago

  • Related to Bug #8745: Chromatic Aberrations module causes saturation shift added

#10 Updated by Roman Lebedev over 5 years ago

  • Related to Bug #8318: Chromatic abberations works randomly for display added

#11 Updated by Roman Lebedev about 5 years ago

  • Has duplicate Feature #10020: Chromatic aberration improvement added

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