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IXUS 100 (SD780) - is CHDK RAW really beneficial?

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Offline ixussuxi

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Re: IXUS 100 (SD780) - is CHDK RAW really beneficial?
« Reply #10 on: 09 / August / 2010, 05:13:44 »
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I looked a bit more carefully at chromatic aberration in the DNG files, using the free tca_correct app. There is a small amount of CA, mostly at the wide end of the zoom. Here's the dcraw parameters at various focal lengths. So at 5.9mm, say, dcraw command line would include '-C 0.9996 0.9993'. At the widest end this implies relative movement by distances of up to 1 or 1.5 pixels.

Focal length, red mag, blue mag
5.9mm  0.9996 0.9993
7.2mm  0.9997 0.9994
8.7mm  0.9997 0.9996
10.6mm 0.9997 0.9998
12.5mm 0.9997 0.9999
14.8mm 0.9999 1.0001
17.9mm 1.0001 1.0003

Here's a sample of the results at 5.9mm (ISO 100). Left is the uncorrected DNG, middle the corrected DNG and right Canon's JPEG. All 500% crops.



There is a fair bit of noise reduction applied to the DNGs (dcraw -n 150) but still not as much as Canon appears to use.
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Offline ixussuxi

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Re: IXUS 100 (SD780) - is CHDK RAW really beneficial?
« Reply #11 on: 09 / August / 2010, 10:38:35 »
Another comparison - 100% crop from centre frame. Processed DNG on left and Canon JPEG on right. The in-camera sharpness is set to minimum (value=0). Even then Canon's sharpening looks pretty heavy, with prominent white haloes around the shapes.

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