Bug in all CHDK DNG 1.3 files prior to Feb 18 2017 (trunk r4756) ?

waterwingz

12138

« on: 25 / February / 2017, 17:52:39 »

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Caught this thread in the dpreview.com forum last week : Software to process CHDK raw files from Canon compacts?

Apparently there has been a bug in CHDK DNG 1.3 bad pixed correction opcodes for some time. It has now been fixed in the autobuild stable and development releases but I'm kind of surprised nothing was reported here as well

If I understand the problem correctly, the Bayer pattern used to create bad pixel correction opcodes for DNG 1.3 was not correct. (A Bayer pattern defines which pixels are have red, green, or blue filters in front of them). This would cause post-processing software to incorrectly "fix" bad pixels when using CHDK generated DNG 1.3 images.

philmoz send one user a command line script to repair a few existing images.

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Ported : A1200 SD940 G10 Powershot N G16

philmoz

3450

Re: Bug in all CHDK DNG 1.3 files prior to Feb 18 2017 (trunk r4756) ?

« Reply #1 on: 25 / February / 2017, 18:39:02 »

I suspect Adobe has changed the algorithm they used to fix the bad pixels.
Previously, even though the bayer pattern was wrong, PS & LR still seemed to do an OK job, so the problem was not readily noticeable.

Attached is the source for the program I created to fix existing files.

Phil.

fixdng.c (3.86 kB - downloaded 48 times.)

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CHDK ports:
sx30is (1.00c, 1.00h, 1.00l, 1.00n & 1.00p)
g12 (1.00c, 1.00e, 1.00f & 1.00g)
sx130is (1.01d & 1.01f)
ixus310hs (1.00a & 1.01a)
sx40hs (1.00d, 1.00g & 1.00i)
g1x (1.00e, 1.00f & 1.00g)
g5x (1.00c, 1.01a, 1.01b)
g7x2 (1.01a, 1.01b, 1.10b)

icameisaw

21

Re: Bug in all CHDK DNG 1.3 files prior to Feb 18 2017 (trunk r4756) ?

« Reply #2 on: 02 / February / 2020, 06:46:33 »

Thank you. I've used gcc 9.2.1 to compile this..

.. but DNG files that have this fix applied - and have definitely been changed - still show the preview as purple and won't load in DxO's PhotoLab, and still won't load in any of Skylum's programs (Luminar, AuroraHDR, Photolemur).

(Affinity Photo will open both the 'before fix' and 'after fix' files, so some software / library will open the buggy DNGs.)

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