SNS-HDR and Raw Chromatic Aberration

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SNS-HDR and Raw Chromatic Aberration

Postby den » Thu Jul 12, 2012 6:05 pm


Starting with program v1.4.22.1 for Lite/Home/Pro, noise reduction was introduced utilizing DCoffin's "dcraw.exe -n <num>" [set threshold for wavelet denoising]... [ref:]

...Please consider doing the same for Chromatic Aberration correction in the 'dcraw' Raw conversion as well... ...i.e., "dcraw.exe -C <r b>" ["Enlarge the raw red and blue layers by given factors, typically 0.999 to 1.001, to correct chromatic aberration."]

The following illustration has two duplicate 295x295 pixel 1:1 image area crops of a single Canon EOS-350D CR2 file "dcraw" converted to tiff... ...the only difference in the "dcraw" conversion options is "-C" as shown. The conversion tiffs were then tone-mapped using SNS-HDR Lite with a Default preset...
IMG_9936_dcraw_CA_correction_SNS-HDRLitev14221-default_1-1ZF.jpg (105.69 KiB) Viewed 8539 times

This may be a challenge to implement because of the generation of 1-3 pixel wide image dimension edge artifacts which may confuse multiple image alignment and de-ghosting algorithms.

More sophicated CA correction methods have been suggested but when CA is corrected before "image merge" and "tone-mapping" of the SNS-HDR auto-workflow... ...the product is much improved...

...especially for those of us that work with nature landscapes and moderate quality zoom lenses.

Thank you for the consideration...
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Re: SNS-HDR and Raw Chromatic Aberration

Postby den » Wed Jul 18, 2012 9:28 am

For those who would wish to explore with there own image data, here is a table of "Red_shift" and "Blue_shift" values where the "Blue_shift" is half of the "Red_shift" which seems to be typically generic when using a Canon EOS-350D camera with an EFS 17-85mm 1.4-5.6 IS USM lens... ...and image data captured with an ISO 100 setting.... ...I really have no way to verify that this ratio of Red to Blue shifts is generic for other camera/lenses.

"dcraw.exe -C <r b>" Correct chromatic aberration
.."Red" .."Blue"
0.99800 0.99900
0.99825 0.99913
0.99850 0.99925
0.99875 0.99938
0.99900 0.99950
0.99925 0.99963
0.99950 0.99975
0.99975 0.99988
1.00000 1.00000 ..Default (no correction)
1.00025 1.00013
1.00050 1.00025
1.00075 1.00038
1.00100 1.00050
1.00125 1.00063
1.00150 1.00075
1.00175 1.00088
1.00200 1.00100
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Re: SNS-HDR and Raw Chromatic Aberration

Postby Sebastian Nibisz » Mon Jul 30, 2012 10:41 am

I'll try to add this option.
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Sebastian Nibisz
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