Difference between revisions of "Gamma"
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(some extra framebuffer info) |
(add alpha premultiplication) |
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Line 7: | Line 7: | ||
The corollary is: | The corollary is: | ||
* Image files loaded as textures should be converted from sRGB to RGB (but some decoders do this for you!) | * Image files loaded as textures should be converted from sRGB to RGB (but some decoders do this for you!) | ||
+ | * Since alpha is linear, [[Premultiplied alpha|alpha premultiplication]] should happen in linear space, i.e. after converting to RGB [http://ssp.impulsetrain.com/gamma-premult.html] | ||
* The shader responsible for putting the final pixels on the screen should have a gamma correction step doing: | * The shader responsible for putting the final pixels on the screen should have a gamma correction step doing: | ||
:<source lang="GLSL"> | :<source lang="GLSL"> | ||
Line 21: | Line 22: | ||
</source> | </source> | ||
− | Note, however, that OpenGL may also perform this step for you on any on-screen framebuffers (i.e. the default framebuffer) if you do < | + | Note, however, that OpenGL may also perform this step for you on any on-screen framebuffers (i.e. the default framebuffer) if you do <code>glEnable(GL_FRAMEBUFFER_SRGB)</code>. |
== See also == | == See also == |
Revision as of 10:27, 19 December 2019
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