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Author Topic: Mysterious color/saturation gradient  (Read 1432 times)

Hening Bettermann

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Mysterious color/saturation gradient
« on: May 15, 2015, 05:19:35 pm »


I have an image that shows a color gradient for which I have no explanation. It is a tree against sky on an overcast day. The image gives the impression of an overall yellow tint in the central part. That is an optical illusion, the sky behind the branches is blown and hence white, it is only the branches that are yellow. But only in the central part. In the periphery, the branches look more neutral, even though they are yellow if measured with the Digital Color Meter.

The phenomenon is most clearly visible in the +4 EV frame of an exposure triplet. The screen shot shows the upper half of this frame, displayed in Iridient in my own camera profile with WB 6500, tint 0.(Non-DNG numbers).

Regardless which WB I choose, the central branches look colored, those in the periphery look grey.

The camera is an a7r, the lens an OM Zuiko 2.8/24 at f/8, 1/6 second for this frame, ISO 64.
The phenomenon is present on the series of 3 exposure triplets on this subject, and on a single triplet shot of the same subject the same day from another angle with the Zuiko 2.8/28. This was the 30. of december 2014, temperature around or slightly below zero degrees Celsius. The phenomenon is not present on a single shot taken on a sunny 3rd september the same year with the 28 mm Zuiko, nor on some shots with the FE Sonnar 2.8/35 taken in summer. It may seem that it is about temperature.

Does anybody have an explanation, or similar experience?

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