DngDecoder: improve ColorMatrix extraction

[kmilos]

See https://discuss.pixls.us/t/dng-hdr-created-in-dt-has-unsupported-input-profile/32528

Not really implementing "rationals support" throughout (I'll bring the comment back in), but should be an ok workaround (better than returning a zero matrix).

[codecov]

Codecov Report

Base: 60.23% // Head: 60.23% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (6d7ce20) compared to base (c18d01b).
Patch coverage: 69.56% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #380   +/-   ##
========================================
  Coverage    60.23%   60.23%           
========================================
  Files          206      206           
  Lines        12526    12535    +9     
  Branches      1749     1752    +3     
========================================
+ Hits          7545     7551    +6     
- Misses        4842     4845    +3     
  Partials       139      139           

Flag	Coverage Δ
integration	48.00% <76.19%> (+0.01%)	⬆️
rpu_u	48.00% <76.19%> (+0.01%)	⬆️
unittests	22.00% <0.00%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/librawspeed/decoders/DngDecoder.cpp	51.53% <69.56%> (+0.30%)	⬆️

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[LebedevRI]

Thank you!

[kmilos]

Thanks for merging and extending.

I guess this is now no longer compatible w/ https://github.com/darktable-org/darktable/blob/5a1a1845fa32378daa9db4b5c3a5705051b1ac49/src/common/imageio_rawspeed.cc#L268 as the division will have already been done when the float cast is requested?

[LebedevRI]

Right, it is expected that places like that will have to be updated.