[SOLVED] : Different default raw black and white points for Canon CR2?

Software darktable
1

If I do history stack -> discard history to reset to default I get different raw black/white points for two Canon CR2 files from the same camera with the same lens. Is this correct?

Steps to repeat:

  1. Go to lighttable and select picture.

  2. Go to darkroom and do history stack → discard history.

  3. darkroom → raw black/white point.

  4. Check black level 0-1 and white point.

  5. _Y8A0003.CR2 has black level = 513 and white point = 14008
    0Y8A6784.CR2 has black level = 2047-2049 and white point = 14448.

  6. Expected result: black levels and white point depends on camera only and should be the same, since both are Canon CR2 from same camera sensor Canon 5D mk IV (and the same lens EF 24-70 mm f/2.8).

_Y8A0003.CR2 (42.0 MB)

0Y8A6784.CR2 (35.6 MB)

Why do the raw files get different default black levels and white points in darktable → darkroom → raw black/white point?

There is one difference between the files. The _Y8A0003.CR2 has Canon camera internal menu parameter setting color profile = AdobeRGB and 0Y8A6784.CR2 has Canon camera internal menu setting color profile = sRGB, but this should only matter if I generate jpg from camera. (The underscore in filename is Canon’s way to indicate this). The attached files are raw files.

I am using git master darktable 4.3.0+684~g23b0c0abd on Linux Debian 11.6. I have updated LibRaw and rawspeed submolues from git master. Lensfun data base is also updated.

The attached pictures are free to use for all.

2

As far as I know, several cameras have black and white points that vary with ISO. This is even recorded in the EXIF by the camera.
[Edit: exiftool output added while pehar was adding the same info]

Output of exiftool for your files:

0Y8A6784.CR2:

Average Black Level             : 2048 2048 2048 2048
Per Channel Black Level         : 2048 2048 2048 2048

_Y8A0003.CR2:

Average Black Level             : 512 512 512 512
Per Channel Black Level         : 511 512 511 512
3

This is what exiftool reports :

exiftool -H -G -a _Y8A0003.CR2 |grep White
[EXIF]          0xa403 White Balance                   : Auto
[MakerNotes]    0x0007 White Balance                   : Auto
[MakerNotes]    0x0006 White Balance Red               : 0
[MakerNotes]    0x0007 White Balance Blue              : 0
[MakerNotes]    0x030e Normal White Level              : 12735
[MakerNotes]    0x030f Specular White Level            : 14008

exiftool -H -G -a _Y8A0003.CR2 |grep Black
[MakerNotes]    0x0009 Black Mask Left Border          : 0
[MakerNotes]    0x000a Black Mask Top Border           : 0
[MakerNotes]    0x000b Black Mask Right Border         : 0
[MakerNotes]    0x000c Black Mask Bottom Border        : 0
[MakerNotes]    0x0146 Average Black Level             : 512 512 512 512
[MakerNotes]    0x030a Per Channel Black Level         : 511 512 511 512

exiftool -H -G -a 0Y8A6784.CR2 | grep White
[EXIF]          0xa403 White Balance                   : Auto
[MakerNotes]    0x0007 White Balance                   : Auto
[MakerNotes]    0x0006 White Balance Red               : 0
[MakerNotes]    0x0007 White Balance Blue              : 0
[MakerNotes]    0x030e Normal White Level              : 13135
[MakerNotes]    0x030f Specular White Level            : 14448

exiftool -H -G -a 0Y8A6784.CR2 | grep Black
[MakerNotes]    0x0009 Black Mask Left Border          : 0
[MakerNotes]    0x000a Black Mask Top Border           : 0
[MakerNotes]    0x000b Black Mask Right Border         : 0
[MakerNotes]    0x000c Black Mask Bottom Border        : 0
[MakerNotes]    0x0146 Average Black Level             : 2048 2048 2048 2048
[MakerNotes]    0x030a Per Channel Black Level         : 2048 2048 2048 2048

so darktable is correct.

4

@kofa, @pehar Thanks for checking.

I agree this is due to different ISO setting. I forgot to consider this factor.