Maintenance and read more Dng exif colordata

[jenshannoschwalm]

DNG Exif: Use AnalogBalance, read more tags and maintenance

Now also read Exif.Image.AnalogBalance and Exif.Image.ForwardMatrix.
To allow easier checking of read exif data we initialize the matrixes with usable defaults instead of marking them as invalid and keep track about found data via gbooleans.
Avoid reading all dng tags if no version has been provided.

Name all matrixes as used in the DNG specs to avoid confusion.

For easy of maintenance all Illuminant specific data are kept in struct dt_dng_illuminant_data_t illuminant_data having struct dt_dng_illuminant_data_t per Illuminant.

• temperature
• human readable Illuminant name for better logs
• the xy coordinate
• the CA matrix to transform illuminant data to D65

Implemented use of Exif.Image.AnalogBalance if provided.

Added pretty extensive information about found tags and used matrixes via -d imageio.

This all requires re-read exif data - done via user request button or fresh import - so no break of old edits.

Note about currently unsupported dng features:

1. According to DNG specs we would have to interpolate between illuminants if there is no given D65 illuminant and at least 2 provided illuminant temperatures are one below and one above D65.
2. To improve quality the specs describe and favor the usage of ForwardMatrix if provided. There seems to be more maths involved (matrix diagonalisation ...).
3. The specs describe how to handle DT_LS_Other illuminant.
4. No support for 4 channel images

Camera DNG files with (1) or (3) are still pretty rare, for (2) there are at least files from sigma.

If we want to have dt progress in this field it would be very nice to get hold on such samples. Thus we check for these cases, report in log and ask the user for feedback via control log to have better chances to get hold on such images to investigate and test implementations.

Tag problematic DNG image files

As commented in commit cf9d9f6 there a dng files still problematic for darktable.
While reading exif data they now automatically are tagged with "darktable|github|dng_issue"
so they can be found easily by the user.

[jenshannoschwalm]

1. Release note would be "DNG files make use of AnalogBalance information"
2. Not sure i will be able to implement at least the ForwardMatrix correction for 5.0 so let's go with this for now. At least the code is more easy to read/use now so chances might be better other people stepping in ...

[kmilos]

Nice! Too bad RPU is down so we can recheck existing samples...

One question, as I'm not too familiar w/ the WB nor CC internals:

I noticed the iPhone 16 DNGs (needs JPEG XL support in rawspeed though) have 1 1 1 for AsShotNeutral, and AnalogBalance that is not identity. (Maybe there are other devices doing this as well, but can't check RPU). Rawspeed will populate wb_coeffs as 1 then. Are there any side effects on WB and/or CC then?

[jenshannoschwalm]

I guess this pr would help for those images. Could you share one?

[kmilos]

Can't remember where I found a sample, couldn've been here...

[TurboGit]

Needs a rebase and conflict resolution after the big code cleanup.

[kmilos]

@jenshannoschwalm That link doesn't seem to contain raws... I now remembered I got the one sample I have from here.

[TurboGit]

Looks good, thanks!

[TurboGit]

Thanks!

[TurboGit]

@jenshannoschwalm : Can you draft a release note entry please? TIA.

[jenshannoschwalm]

Release note:

1. Added support for exif tags 'AnalogBalance' used for color calibration and LinearResponseLimit used in highlights reconstruction.
2. If we find currently unsupported color calibration data in DNG specific tags we tag the image by darktable|issue|no-samples for better support,