Sony A7xxx Posterization and Colored Banding (Part 2)

Started Dec 8, 2018 | Discussions thread
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sharkmelley
sharkmelley Senior Member • Posts: 2,589
Sony A7xxx Posterization and Colored Banding (Part 2)
10

This new thread picks up from the previous thread which filled up all too quickly:

Sony A7III Posterization and Colored Banding

I've changed the title from A7III to A7xxx because it is certain that more than one camera is affected.

For those who see no need for another thread on this subject, please feel free to ignore it, without comment

I'll try to summarize what we know so far:

The issue under discussion is coloured banding in the shape of 12-sided polygons. It's rare to see a complete pattern in a real-life photo but here's an example from over 3 years ago:

Sony RX1 Example

On that camera, the artefact could be disabled by switching off vignetting correction. Unfortunately this is no longer the case on (some or all) cameras in the A7xxx series.

A more recent discussion is here:

The effect of in-camera Lens Compensation and more ...

The effect only happens for lenses that are recognised by the camera and for which correction parameters are available. A table of numbers similar to this will be found in the EXIF:

Vignetting Corr Params : 0 32 96 224 384 576 864 1248 1728 2368 3200 4256 5472 6816 8224 9632

If the parameters are all zero then there is no problem:

Vignetting Corr Params : 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Here are a few more points of interest:

  • The artefact is "baked into" the raw pixel data of the raw file. It is not applied by the raw converter.
  • On the A7III v2.0 firmware it happens even with in-camera vignetting correction switched to off. Similarly on the A7RII.
  • The pattern of coloured polygons is the same whether the vignetting correction is on or off.
  • The artefact is typically found in darker areas of an image that are pushed in processing. Note that the processing doesn't cause the problem - it simply reveals what is already there.
  • Some lenses are much more affected than others. It's probably related to the amount of vignetting.

The same issue was found on the A7RII over a year ago. At the end of a long thread the diagnosis was the same:

Cause of green/purple concentric rings in fog photo?

The OP proved that the rings appeared even with A7RII in-camera vignetting correction set to off. They disappeared when he disabled the electronic contacts on the lens. Taping over them is equally effective.

In short, we are no further forward than those A7RII experiments of one year ago. There is some unknown correction being applied to the raw camera data when the camera is paired with any lens for which correction data is available. There is no user control over this unknown correction - it is applied even when all lens corrections are switched off. The unknown correction introduces 12-sided polygon coloured banding into the data which can become obtrusive under certain circumstances.

Mark

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Takahashi Epsilon 180ED
H-alpha modified Sony A7S
http://www.markshelley.co.uk/Astronomy/

 sharkmelley's gear list:sharkmelley's gear list
Sony a7S Nikon Z6 +1 more
Sony RX1
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