Converting and processing linear exr's


#1

hello.
I’m trying to process linear exr’s (with alpha) and output 8 bits sRGB png.
something like this :
gmic -o ima.exr -gimp_emulate_film_various 56,100,0,0,0,0,0,0,0 -o ima.png
I tried a lot of things already but I’m totally lost now.
I usually get black frames.tried to -mul 256 but colors are always wrong…
thanks in advance
luc


(David Tschumperlé) #2

I’m wondering why you start with -o ima.exr, shouldn’t it be -i ima.exr ?


#3

sorry.a typo.yes it’s -i


(David Tschumperlé) #4

Ok :slight_smile: Could you put this file somewhere so I can try by myself ?

EDIT: I suppose the .exr is read with a different value range, adding -n 0,255 just after the file input could help.


#5

ok.just needs a gamma 2.2 and it works!
-apply_gamma 2.2 -n 0,255
thanks a lot
luc


#6

If you want linear to sRGB output it should be something like this at the end:

-n 0,255 -rgb2srgb -o file.png

(Carmelo Dr Raw) #7

It looks like this command assumes that the input EXR data is in linear sRGB colorspace… or does G’MIC read the input color space primaries from the EXR itself?


#8

That’s correct, it does srgb “gamma” encode only. I expect color space is not read from the EXR, but I could be wrong.

Edit: on the same subject, if such things were supported I’d expect the data to be made available (i.e. loaded into an image on the stack) but not automatically applied. That way the user has control over it’s use and could perhaps decide whether to load it.