sRGB color space problem?

[Rydgel]

Hello,

It seems I have an issue to display my texture with the correct colours. It seems like everything I tried didn't change anything.

Here is a few excerpt of how I load the texture and draw it:

use opengl_graphics::{GlGraphics, Texture, TextureSettings};
use graphics::{Context, Transformed};
use graphics::draw_state::DrawState;
use graphics::Image;
// ...
let mut texture_settings = TextureSettings::new();
texture_settings.set_convert_gamma(true);
texture_settings.set_compress(true);
let texture = Texture::from_image(&img, &texture_settings);
// ...
// in the drawing method
Image::new().draw(&self.texture, &DrawState::new_alpha(), transf, gl);

So changing the set_convert_gamma value to false or true does nothing.
Creating the Window with .srgb(true) or .srgb(false) does nothing.

I'm on OS X. I'm using Rust nightly rustc 1.16.0-nightly (24055d0f2 2017-01-31)
Cargo packages:

[dependencies]
itertools = "0.5.9"
piston = "0.31.3"
piston_window = "0.64.0"
piston2d-graphics = "0.21.1"
pistoncore-sdl2_window = "0.40.0"
piston2d-opengl_graphics = "0.40.0"
rand = "0.3.15"
find_folder = "0.3.0"
image = "0.12.2"

And here is the texture image itself

[bvssvni]

Seems that none of the backends implements gamma conversion for textures.

[Rydgel]

Maybe I can try to convert my texture with something like gamma_srgb_to_linear?

[bvssvni]

Yes, you can do this manually.

I wonder why it shows wrong colors, because it seems your texture is in sRGB. This should be enabled here https://github.com/PistonDevelopers/opengl_graphics/blob/master/src/back_end.rs#L338, converting to linear color space in the shaders, and back when writing to the frame buffer.

[Rydgel]

Yeah I saw that, it's weird. I even tried with other images, same problem.

[Rydgel]

I even tried several Window libraries, currently using SDL2Window, but tried GLFW and Glut with the same result.

[Rydgel]

Doing a gamma_srgb_to_linear conversion on my texture fixes the issue for me.
It's weird since it seems that the reverse function is done inside the drawing function.

[adfaure]

Hello,
I have the same issue here.

I will do it manually too, but will it be fixed in a future release ?
Thanks a lot !

[expenses]

@Rydgel @adfaure Would you mind sharing the code that you used to perform the conversion? I'm having trouble with this step.

Edit: this is what I've got so far:

fn to_f(value: u8) -> f32 {
    value as f32 / 255.0
}

fn to_u(value: f32) -> u8 {
    (value * 255.0) as u8
}

fn load_texture(filename: &str, texture_settings: &TextureSettings) -> Texture {
    let mut image = image::open(filename).unwrap().to_rgba();

    for pixel in image.pixels_mut() {
        let conv = gamma_srgb_to_linear([to_f(pixel[0]), to_f(pixel[1]), to_f(pixel[2]), to_f(pixel[3])]);
        pixel.data = [to_u(conv[0]), to_u(conv[1]), to_u(conv[2]), to_u(conv[3])];
    }

    Texture::from_image(&image, texture_settings)
}

[Rydgel]

@expenses Doing this basically: https://github.com/Rydgel/rust-rogue/blob/b09400daec0a84a82d6b357e9ffa5f55c68afd5c/src/drawings/sprites.rs#L64

[expenses]

@Rydgel So I was on the right track! Thank you very much!

[Aerolivier]

Am I right in thinking this can be solved by tagging the texture data with the GL_SRGB8 or GL_SRGB8_ALPHA8 formats? ( according to https://www.khronos.org/opengl/wiki/Image_Format#sRGB_colorspace )

As far as I understand, quantising the linear values to 8 bits (like suggested as a workaround) leads to a loss of integrity in the image ( as demonstrated at http://tulrich.com/webgl/rgb/linear_vs_srgb.html ).

I'd like to fix this, but I'm not familiar with the code base. Any pointers or should I just start getting stuck in?
Edit: Sorry for retracting the above, but I'm now considering a different course of action.