DNG BlackLevel handling when cpp != 1

[LebedevRI]

@LebedevRI @alexvanderberkel I got darktable decoding dual pixel dng files.

There is one more thing in rawspeed that "requires relaxing". bool DngDecoder::decodeBlackLevels(const TiffIFD* raw) { in DngDecoder.cpp should accept cpp==2 too.

So i suggest it to be

 if ((mRaw->getCpp() < 1) || (mRaw->getCpp() > 2))
    return false;

Can you agree here? And could you modify this or do you want me to do a pr? BTW it would be nice to push current rawspeed to dt :-)

Originally posted by @jenshannoschwalm in https://github.com/darktable-org/rawspeed/issues/214#issuecomment-570887227

More specifically, as per https://www.adobe.com/content/dam/acom/en/products/photoshop/pdfs/dng_spec_1.4.0.0.pdf, all that blacklevel info is not at all specific to cpp=1/cpp=2. See BLACKLEVELREPEATDIM, BLACKLEVEL, BLACKLEVELDELTAV, BLACKLEVELDELTAH. Which only highlights how broken the current 4-channel mRaw->blackLevelSeparate is.

[jenshannoschwalm]

Ok, i agree on missing proper blacklevel support.

You know http://wwwimages.adobe.com/www.adobe.com/content/dam/acom/en/products/photoshop/pdfs/dng_spec_1.5.0.0.pdf ? There is even more to be worked on.

Do you have priority list of more "things-to-be-fixed" regarding dng?

[LebedevRI]

Ok, i agree on missing proper blacklevel support.

You know http://wwwimages.adobe.com/www.adobe.com/content/dam/acom/en/products/photoshop/pdfs/dng_spec_1.5.0.0.pdf ?

Oh, nice, i should update my bookmark then.

There is even more to be worked on.

Do you have priority list of more "things-to-be-fixed" regarding dng?

I don't think i have any list regarding DNG. (well, other than the general issue of 'multi-image raw support')

[madwyn]

Thanks for pointing me to the right direction. I'm wondering will this be fixed in the develop branch?

RGB DNG files have cpp=3 and they also can have black levels label 50714 Black Level.

It's confusing that black level handling needs to consider cpp, I can understand <1 or >3 looks "bad".

[LebedevRI]

Just so we have frame of reference, can you upload here (you may need to zip it first) some such DNG?

[parafin]

By RGB DNG do we mean LinearRaw DNG with SamplesPerPixel equal to 3?

[LebedevRI]

By RGB DNG do we mean LinearRaw DNG with SamplesPerPixel equal to 3?

Yes. I'd be particularly interested in some sane sample, with different black levels in all 3 channels (as opposed to the dual-pixel dng's..)

[madwyn]

Edit: Removed temporary link.

---

The file size is well over 10MB, here is the link:

[madwyn]

The file was originally a X3F image converted by x3f tools to DNG, then I used Adobe DNG converter "converted" it again to get some compression. I would assume the tags should be intact.

@parafin, you are right, it's LinearRaw with cpp=3.

[LebedevRI]

_SDI0247.X3F.dng-partaa.zip _SDI0247.X3F.dng-partab.zip _SDI0247.X3F.dng-partac.zip _SDI0247.X3F.dng-partad.zip

[madwyn]

By RGB DNG do we mean LinearRaw DNG with SamplesPerPixel equal to 3?

Yes. I'd be particularly interested in some sane sample, with different black levels in all 3 channels (as opposed to the dual-pixel dng's..)

I extracted the values using exiftool, they look identical:

50714 Black Level                     : 206.875 206.875 206.875

I also run dng_validate against this file, no errors. So I assume it's a valid DNG file with legal tags.

[madwyn]

When reading the code, I also noticed that the White Level tag is always treated as an integer filed, but according to the DNG spec, it's a field contains as many values as the "plane" number.

Will this behaviour get changed, just like black levels?