Darktable 2.4 - different PPG demosaic results on 2 machines



Hi there,
I have one laptop with ubuntu 18.04 which was upgraded from 16.04. Darktable is from pmjdebruijn repository. Recently I have installed fresh ubuntu 18.04 on my second laptop and duplicated my working environment. Darktable on my new laptop is also from pmjdebruijn repo.

During my switch to new laptop I couldn’t get the same results on both laptops. All my work is on external drive therefore when opening RAW image the pipeline should be consistent. Occasionally I’m also examining my work on third computer with Ubuntu 16.04 and results are consistent with the old laptop.

On my new laptop images were flat, desaturated. I was suspecting that monitor profile was improper so I have recalibrated it (it’s Eizo) with no luck. Only after few days of researching I figured out that when I switch demosaic algorithm from PPG to other like AMaZE the image looks normal as on the old laptop. Generally mangling with demosaic on old laptop gives no visible improvement so I’m using PPG.

In the end I’m using AMaZE by default on my new laptop but I’m curious is there any logic behind such behavior? Different library somewhere?

(Thomas) #2

I think it is just a matter of module presets stored in the config-folders of the installations. Why these differed between upgrade and fresh installation, is difficult to understand in hindsight.


Yes, the differences are between old laptop with ubuntu upgraded to 18.04 and the new one with the fresh installation of the 18.04. I have my raw files on the external drive so in both cases the same xmp file is read. When I try new raw file without xmp attached it’s the same. In the fresh installation colors are washed out until I change demosaic to AMaZE.

(Thomas) #4

But not the module presets. Those are stored in the home folders.


Hm. In both cases the demosaic module have the same parameters: PPG and everything turned of. Is there something more?

(Thomas) #6

Not that I know of.

(Mica) #7

Are your working color profiles set to the same thing?


I have single Eizo display and the profile is the same on both laptops (triple checked it using md5sum). ICC on darktable/color/[in|out] are the same. Maybe ArgyllCMS version is different. Do not remember.

(Massimo Bill) #9

But are you seeing this also when zoomed in less than 50%?

If I’m not wrong, the demosaicing step shouldn’t be done (on display rendering) by darktable if the zoom is not greater than 50%… right?

Or actually… depending on the core options, it may be that PPG is always done, while the slower ones are only applied if zoomed in more than 50%. You may have a look in the core options.

Are you seeing this change in the image between different demosaic settings also when zoomed at less than 50%, then? What about when you change “demosaicing for zoomed out darkroom mode” in the core options?

Have you checked if this “core option” is the same if all of your darktable instances?


Exported JPG are different so this may not be it.
Let me try to find a good example and I will try to show the pictures.