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Olympus E-510 analog channel gain offset

Hi, I got an Olympus E-510 and currently developing rendering using raw Bayer data.
Thanks to Dave C's "DCRAW", I'am able to hack on it and get the raw bayer data out.
I've observed channel unbalance between Gr and Gb channel. On my camera, it has about 2% difference in gain, i.e., Applying gain equalization with Gr / 1.02 = Gb * 1.02, in order to get smooth gray field without horizontal grid lines.
On other people's camera (ORF raw data from web sites), it requires different channel gain offsets.
I believe the CMOS sensor is from Panasonic.

I have the following questions:
Does Gr and R share the same analog channel? Anyone has the sensor spec?
Does the maker note contains the channel gain offset calibration data? If so, how to decode it?

By the way, on E-400 (Kodak CCD sensor) does not exhibit such gain offset problem.

Shane

Shane Hu
Thu, 05 Mar 2009 00:15:42 +0000

Gr and Gb often differ, and not with a fixed percentage.
Gr usually goes up in reds, and down in blues.
For good compensation you will need to map R, G, B values to a Gr correction.
Some cameras compensate for this internally.

Set BayerGreenSplit to >0 to tell the debayer code that there is a split.

See for example http://www.kodak.com/global/plugins/acrobat/en/business/ISS/ . . .

Lars

LarsB
Tue, 27 Apr 2010 18:15:49 +0000

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