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Author Topic: Flat field correction for CGATS  (Read 3790 times)
Iliah
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« on: March 11, 2013, 10:46:45 AM »
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New version of RawDigger available for download at http://www.rawdigger.com/node/194 includes the flat field correction based on a separate shot of a uniform surface replacing the target.

To illustrate how the flat field works I used a Zeiss 2/50 Makro lens on a Olympus OM-D EM-5. Contrary to normal, the aperture was fully opened and the traget was filling the frame. That allows to see sort of real life scenario. The target and reference white sheet of regular thick matt paper were not perfectly flat as I used clips to mount it instead of more fancy hold I normally do.

The shot of the target, raw

The reference shot for the flat field, raw

The CGATS file without the flat field compensation, if converted to bitmap it looks like


The CGATS with flat field correction applied, if converted to bitmap it looks like


It is interesting to compare the corrected and non-corrected for flat field files (CGATS data or JPEG renditions) for the difference between the RGB values on the peripheral and central white patches, as well as between neutral patches in different locations on the periphery of the target.

For the reference, the values measured off the target itself and generic RGB rendition of the reference values



Now, the profile can be calculated using the free Argyll CMS, one of the ways:

txt2ti3 -v -i CGATS_From_RD.txt Orig_Digital_ColorChecker_SG.txt Data4ProfileCalculation

colprof -v -A "CameraMake" -M "CameraModel" -D "Profile Description" -C "Your Copyright" -y -qu -aG -nc -O ProfileName.icc Data4ProfileCalculation

You can also use http://www.rawdigger.com/node/193 for questions, bug reports, and feature requests.
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