Gamma

Quick rules of thumb, since I can never remember which is which:

• RGB = linear space
• sRGB = gamma space
• most image files store sRGB
• sRGB is unfit for blending

The corollary is:

• Image files loaded as textures should be converted from sRGB to RGB (but some decoders do this for you!)
• Since alpha is linear, alpha premultiplication should happen in linear space, i.e. after converting to RGB [1]
• The shader responsible for putting the final pixels on the screen should have a gamma correction step doing:

const float gamma = 2.2;

out vec4 color;

void main()
{
    // ...

    color = pow(color, 1. / gamma);
}

Note, however, that OpenGL may also perform this step for you on any on-screen framebuffers (i.e. the default framebuffer) if you do glEnable(GL_FRAMEBUFFER_SRGB).

See also

• https://blog.johnnovak.net/2016/09/21/what-every-coder-should-know-about-gamma/
• https://stackoverflow.com/questions/23026151/do-i-need-to-gamma-correct-the-final-color-output-on-a-modern-computer-monitor
• https://www.khronos.org/opengl/wiki/Framebuffer#Colorspace
• https://en.wikipedia.org/wiki/Gamma_correction
• https://www.cambridgeincolour.com/tutorials/gamma-correction.htm
• http://chilliant.blogspot.com/2012/08/srgb-approximations-for-hlsl.html