CR3 to Tiff conversion results in different brightness levels

Submitted by LelliD on

Hi,

I have two .CR3 files (Canon M50 Mark II), which were taken with exactly the same parameters, and the same illumination, so I would expect the same brightness level (and the .jpeg files indeed have the same brightness).

When I'm converting the .CR3 files to 16-bit TIFF files using the latest bits of LibRaw (2021-10), I get two TIFF images with quite different brightness levels.

Converting the .CR3 files first to .DNG files, using Adobes DNG converter, and then convert those .DNG files to 16-Bit TIFF files with LibRaw result in the same brightness level, as expected.

Is there any 'hidden' factor in the .CR3 files, which is not taken into account in the current LibRaw version?

Maybe it has something to do with the fact that those pictures are slighly overexposured, because I can't see this effect with pictures which are not overexposured.

Thanks, Lellid

Forums: 

It is very difficult to

Submitted by lexa on

It is very difficult to discuss the problem in abstract without having sample files

-- Alex Tutubalin @LibRaw LLC

Providing the files

Submitted by LelliD on

Hi,

I can provide the files (as long as they will not appear in a public forum). I think it would suffice to upload the two .CR3 files (35 MB each). Can you please show me a way to upload them?

Lellid

We never publish files that

Submitted by lexa on

We never publish files that are sent to us without explicit permission.

Please use any file sharing service (e.g. WeTransfer/free option) and send the link to info@libraw.org

-- Alex Tutubalin @LibRaw LLC

(copied from E-mail, probably

Submitted by lexa on

(copied from E-mail, probably this answer may be interested to public)

To turn off automated maximum adjustement use dcraw_emu -c 0 (imgdata.params.adjust_maximum_thr = 0)

-- Alex Tutubalin @LibRaw LLC

Thanks - seems to work now

Submitted by LelliD on

Hi Alex,

with dcraw_emu using -M -o 0 -c 0 -j -W -q 1 -4 -T as arguments, both TIFF images converted from CR3 now look equally bright, and the two TIFF images converted from the corresponding DNG files also look equally bright. However, the TIFF images converted from CR3 and DNG differ in brightness. Is this by design?

I'm now trying to figure out how to use it programmatically. The parameter adjust_maximum_thr seems not to be accessible from the libraw_set_... API. I'm using C# with InteropServices. I think I can write such method and amend it to libraw; or better maybe you should consider the addition of this method (something like libraw_set_maximum_threshold).

I already used in my program:

```
libraw_set_no_auto_bright(handler, 1);
libraw_set_bright(handler, 1.0f);

```
so I expected no automatic brightness adjustment anyway.

Thanks, LelliD

Brightness adjustement and

Submitted by lexa on

Brightness adjustement and maximum level adjustement are different things (wrong maximum may/will result into 'pink highlights' problem and auto-adjust works against it).

I agree, set_maximum_adj_threshold should be added to C-API.

-- Alex Tutubalin @LibRaw LLC