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Feature #12014

Profiled denoise: consider Fuji DR setting for noise profile selection

Added by Björn Sonnenschein over 1 year ago. Updated over 1 year ago.

Status:
Incomplete
Priority:
Low
Assignee:
-
Category:
Darkroom
Target version:
-
Start date:
02/15/2018
Due date:
% Done:

20%

Estimated time:
Affected Version:
git master branch
System:
all
bitness:
64-bit
hardware architecture:
amd64/x86

Description

Fujifilm cameras provide a dynamic range setting, which performs underexposure by using an ISO setting one stop lower than the ISO chosen by the user. If the internal JPEG engine is used, the image is processed with a tone curve to match normal exposure, but with highlight detail retained due to the underexposure.
The raw file, however, corresponds to an underexposed image taken with the lower iso setting, but tagged as the regular iso setting. Thus, a DR200 image taken at ISO 400 is in fact an ISO 200 Image, but with the EXIV data reading ISO 400. Profiled denoise does not take the DR setting into account and therefore selects the ISO 400 preset, which is not correct. It would be very useful if the profiled denoise would take the DR setting into account when selecting the noise profile.

DSCF5351.RAF (32.2 MB) DSCF5351.RAF Björn Sonnenschein, 02/16/2018 10:36 AM
DSCF5351.JPG (6.49 MB) DSCF5351.JPG Björn Sonnenschein, 02/16/2018 02:13 PM

Related issues

Related to darktable - Feature #11370: Respecting RawExposureBias tag for Fujifilm RAF filesNew12/18/2016

History

#1 Updated by Tobias Ellinghaus over 1 year ago

  • % Done changed from 0 to 20
  • Status changed from New to Incomplete

Do you have a sample file?

#2 Updated by Björn Sonnenschein over 1 year ago

I have attached a sample file. The Dynamic Range setting is denoted by the field DevelopmentDynamicRange in the MakerNote.
In the sample, DR is 200, which corresponds to 1 stop of underexposure, so that the ISO 400 in the Exiv corresponds to a real ISO 200.
Other possible settings are 100, which is a normal exposure, and 400, corresponding to 2 stops of underexposure.
Only ISO values are possible that still allow the camera to expose at lower ISO. Thus, as the base ISO of Fujifilm cameras is 200, the minimum ISO the user may select with DR 200 activated is ISO 400, and with DR 400 it is ISO 800.

#3 Updated by Tobias Ellinghaus over 1 year ago

Ok, I see. Just one thing I am still not clear about: Does Exif.Fujifilm.DevelopmentDynamicRange always show the same 200 when going down 1ev, or is it always the real ISO value? So, when having the camera set to -1ev and shooting at (nominally) ISO 1600, does that value say 200 or 800?

#4 Updated by Björn Sonnenschein over 1 year ago

Oh, sorry for the ambiguity:
The DevelopmentDynamicRange always refers to the Dynamic Range setting and not to the ISO value. Thus, DevelopmentDynamicRange of 200 indicates a real ISO of 800 for images shot at nominally ISO 1600

#5 Updated by Tobias Ellinghaus over 1 year ago

Could you also upload the corresponding JPEG please? So we can make sure to not change the ISO for that.

#6 Updated by Tobias Ellinghaus over 1 year ago

  • Related to Feature #11370: Respecting RawExposureBias tag for Fujifilm RAF files added

#7 Updated by Björn Sonnenschein over 1 year ago

Of course, here is the corresponding JPEG

#8 Updated by Žilvinas Žaltiena over 1 year ago

Björn Sonnenschein wrote:

Fujifilm cameras provide a dynamic range setting, which performs underexposure by using an ISO setting one stop lower than the ISO chosen by the user. If the internal JPEG engine is used, the image is processed with a tone curve to match normal exposure, but with highlight detail retained due to the underexposure.
The raw file, however, corresponds to an underexposed image taken with the lower iso setting, but tagged as the regular iso setting. Thus, a DR200 image taken at ISO 400 is in fact an ISO 200 Image, but with the EXIV data reading ISO 400. Profiled denoise does not take the DR setting into account and therefore selects the ISO 400 preset, which is not correct. It would be very useful if the profiled denoise would take the DR setting into account when selecting the noise profile.

One important moment here is DR200 + ISO400 is truly ISO200 only if mentioned underexposure isn't compensated in post. If you make +1EV exposure while processing such raw file, you end up with effective (analogue+digital) ISO400. Then noise profile for ISO200 isn't right (too weak), profile for ISO400 (as is currently autoselected) is closer, but still not right. For this to work correctly, there must be separate profiles for ISO and DR setting combinations, because ISO achieved by purely analogue amplification and ISO achieved by analogue combination + digital push may have different patterns.

#9 Updated by Björn Sonnenschein over 1 year ago

I must admit that I don't understand your statement completely.
For Instance, a RAW image Taken with DR200 at nominal ISO 400 is an image taken with ISO 200, but with exposure measured for ISO 400. No digital Gain is applied by the camera. If digital gain is applied with Darktable using the exposure module, this is done after the profiled denoise in the pixel pipeline and thus it doesn't affect the profiled denoise.

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