Convert exr to png file

[Youdiie]

I wanted to convert exr file to png file.
I used the example 1b_convert_exr_to_png, but the color of converted png file was quite different from original exr file.
exr file: (can't upload exr file, so instead screenshot)

converted png file:

I found the comment does the image crate expect gamma corrected data? in tone_map function.
Is that comment related to this problem?
Any comment will be helpful!

[johannesvollmer]

Hi! Yes, this might be the problem. The exr format allows many color spaces, in linear format. Most other software doesn't use linear colors.

Where do your exr images come from?

[johannesvollmer]

The color differences can have many sources, but I think these are the most likely in your case:

• "color space linear versus non-linear" The exr format stores linear colors, but PNG certainly uses non-linear sRGB colors, so you have to perform a conversion
• "tone mapping" The exr format allows for arbitrary brightness, but PNG is only integers from 0 to 255 (or 0 to 1 floats). Thus, the example performs tone-mapping to squash the infinite values into the limited range from 0 to 1. This leads to washed out colors. You can remove this step entirely, if your image has the 0 to 1 range from the start.

[johannesvollmer]

So essentially, remove the calculations from line 45 in the example

exrs/examples/1b_convert_exr_to_png.rs

Line 45 in 0d78600

let clamped = (linear - 0.5).tanh() * 0.5 + 0.5;

[NicTanghe]

This seems like a prerequisite to anny work with exrs.
https://docs.rs/colorspace/latest/colorspace/
Seems sort of abandonned though