Vignette and distorsion correction (for older cams) - Feature Requests - CHDK Forum
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Vignette and distorsion correction (for older cams)

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Offline toinech

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Vignette and distorsion correction (for older cams)
« on: 20 / January / 2012, 19:43:07 »
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Some newer cams apply vignette {and distorsion correction}.
Not sure which one does?
Is it possible to do such correction (at least vignette which seems to be the low hanging fruit here) with older cameras?
Or it is too much processing.
Procedure seems to be simple:
1. Aperture, Focal length => vignette profile (most likely an attenuation factor based on radius)
   Vignette profile is camera dependent - possibly tables or math functions that interpolates the actual vignette of the lens
2. Radius is function of x, y and some reference point x0, y0 (most likely center of the sensor)
3. Multiply the pixel value brighness by reverse of attenuation.

Toine
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Offline reyalp

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Re: Vignette and distorsion correction (for older cams)
« Reply #1 on: 20 / January / 2012, 20:33:04 »
Vignette seems like it should be possible, though probably slow. reverse_bytes in optimized assembler takes a significant fraction of a second. If you can figure out how to program the image processing of Digic, that might be a different story.

You could also do this with a flat frame but this would be even slower. I suppose applying flats could be a menu operation like sum, average and subtract.

I'm not really sure of the value, I would expect most people concerned with this to have an extensive workflow on their PC. Assuming you use raw/dng there would be no quality advantage to doing it on the camera.

Distortion correction seems like it would be harder.
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