LX7 wrong black levels, black/white point hidden parameters?

kofa · September 15, 2021, 7:16am

Please let me know if I should raise github issues for either of the observations below.

#1: Wrong black levels?
I was editing a Panasonic LX7 raw, and found a colour shift when raising exposure.
Without raising exposure:

With raised exposure:

I noticed that the waveform showed different black levels for the channels. I checked in exiftool, and that indicated 128 for all channels, like used in darktable:

Changing the black levels allowed me to fix the colour cast:

#2: Hidden parameter(s)
I created a style using those black points, and applied that to another photo - but the geometry of that picture changed:

It seems that a non-adjustable, hidden parameter, crop right, also changed. I guess this is related to the LX7 being a multi-aspect-ratio camera. I was just wondering why the parameter is hidden.

kofa · September 15, 2021, 8:55pm

It turned out to be a regression

github.com/darktable-org/darktable

Lumix LX7 black point wrong

opened 06:41PM - 15 Sep 21 UTC

kofa73

**To Reproduce** 1. Import raw and sidecar from https://tech.kovacs-telekes.o…rg/files/2021-09-15-darktable-lx7-blackpoint/ 2. Select step 12 in history (this loads the black point values from darktable 3.6, all = 143) 3. Reset the _raw black/white point_ module (this will set the current values, all = 128 4. See colour cast **Expected behavior** Proper black levels are used **Screenshots** ![Screenshot_20210915_202706](https://user-images.githubusercontent.com/3177739/133489977-91dc68e5-df17-441a-bf3e-5ece03d94216.png) **Which commit introduced the error** Probably dae697b @LebedevRI In rawspeed the black value seems to be 150 (neither 128, not 143 that I saw in darktable 3.6), and these lines have not been updated for 7 years: https://github.com/darktable-org/rawspeed/blob/develop/data/cameras.xml#L6008-L6032 Wrong value seems to come from EXIF: ``` kofa@eagle:~/darktable$ exiftool `locate *P1060660.RW2`|grep -i black Black Level Red : 128 Black Level Green : 128 Black Level Blue : 128 ``` **Platform** * darktable version : 3.7.0+1050~g0c01bab23 * OS : Linux - kernel 5.11.0-31 * Linux - Distro : Ubuntu 21.04 * Memory : 64 GB * Graphics card : NVidia 1060/6GB * Graphics driver : 460.91.03-0ubuntu0.21.04.1 * OpenCL installed : yes * OpenCL activated : yes * Xorg : 1:7.7+22ubuntu1 * Desktop : KDE 5.80.0-0ubuntu1 * GTK+ : 3.24.25-1ubuntu4.1 * gcc : 10.3.0 * cflags : none * CMAKE_BUILD_TYPE : RelWithDebInfo

jdneumeyer · September 17, 2021, 4:04am

Seems more like a 7+ year bug with a magic number no one understands. I wonder if Panasonic fixed the black levels in a newer version of their raw format. The fix worked for several samples I tried. I think I tried the GH5, GH5s, G9 and GX9 in addition to my S5. I didn’t try to push the exposure tho. I’ll have to try older camera samples and retest the others.