What does "Linearity Upper Margin" mean?

exiftool -g0:2 -LinearityUpperMargin IMG_4337.CR3   
---- MakerNotes:Camera ----
Linearity Upper Margin          : 12735

There's a black/white level discussion at discuss.pixls.us that speculates:

discuss.pixls.us/t/measure-black-and-white-levels/32082/19

Here is what I meant: raw data non-linearity exceeds 6% when above this value. The value is ISO-dependent.

Thanks

Thanks

Thanks again for your help.

The discussion of black level at

got me to wondering about black level since the LinearityUpperMargin seems to always be 12735 for this camera. It puzzles me.

I diffed two exif outputs from images made from the same scene about one second apart. About the only difference I notice between the two images is focus failed in the first and then the bird moved and focus succeeded in the second with one point on the eye. But, the black level is very different.
Guessing, is the camera trying to give more detail in shadows when not finding the eye of the bird?

Out of focus image SOOC: www.rsok.com/~jrm/raw/IMG_4171.JPG
Raw for out of focus image: www.rsok.com/~jrm/raw/IMG_4171.CR3
diff between two exiftool outputs: www.rsok.com/~jrm/raw/4171-4172.diff
second image after processing: www.rsok.com/~jrm/2023Jun21_birds_and_cats/2023jun01_bunting_IMG_4172c.html

exiftool -G0:2 -s IMG_4171.CR3 > /tmp/4171.txt
exiftool -G0:2 -s IMG_4172.CR3 > /tmp/4172.txt
diff /tmp/417[12].txt > /tmp/4171-4172.diff

170c170
< [MakerNotes:Camera] MeasuredRGGB                : 635 1024 1024 399
---
> [MakerNotes:Camera] MeasuredRGGB                : 679 1024 1024 418
209,214c209,214
< [MakerNotes:Camera] WB_RGGBLevelsAsShot         : 1869 1024 1024 2040
< [MakerNotes:Camera] ColorTempAsShot             : 4756
< [MakerNotes:Camera] WB_RGGBLevelsAuto           : 1869 1024 1024 2040
< [MakerNotes:Camera] ColorTempAuto               : 4756
< [MakerNotes:Camera] WB_RGGBLevelsMeasured       : 1869 1024 1024 2040
< [MakerNotes:Camera] ColorTempMeasured           : 4756
---
> [MakerNotes:Camera] WB_RGGBLevelsAsShot         : 1859 1024 1024 2013
> [MakerNotes:Camera] ColorTempAsShot             : 4784
> [MakerNotes:Camera] WB_RGGBLevelsAuto           : 1859 1024 1024 2013
> [MakerNotes:Camera] ColorTempAuto               : 4784
> [MakerNotes:Camera] WB_RGGBLevelsMeasured       : 1859 1024 1024 2013
> [MakerNotes:Camera] ColorTempMeasured           : 4784
229c229
< [MakerNotes:Camera] PerChannelBlackLevel        : 2047 2047 2047 2047
---
> [MakerNotes:Camera] PerChannelBlackLevel        : 511 511 511 511
236,237c236,237
< [MakerNotes:Image] BaseISO                      : 308
< [MakerNotes:Image] MeasuredEV                   : 11.88
---
> [MakerNotes:Image] BaseISO                      : 259
> [MakerNotes:Image] MeasuredEV                   : 12.12
239c239
< [MakerNotes:Image] TargetExposureTime           : 1/323
---
> [MakerNotes:Image] TargetExposureTime           : 1/256
249c249
< [MakerNotes:Image] MeasuredEV2                  : 21.5
---
> [MakerNotes:Image] MeasuredEV2                  : 22

I figured it out. The change in black level goes with ISO. At ISO less than 320, black level is near 512 and at ISO 320 or higher black level is near 2048.

Thanks again