Asked 4 months ago by SupernovaObserver386
Why does mixing constant and sRGB texture colors yield unexpected results in GLSL shaders?
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Hi, everybody.
I’m experiencing unexpected color blending behavior in my shader. While implementing a highlight feature, I mixed a texture color using mix() with a constant color defined as vec4(0, 0.5, 1, 1). I expected this to represent rgba(0, 127, 255, 1), yet it rendered as rgba(0, 188, 255, 1).
For clarity:
GLSL127 / 255 = 0.4980... ~= 0.5 188 / 255 = 0.7372... ~= 0.75
I observed that this discrepancy doesn’t occur when the color comes directly from a texture loaded with SRGBColorSpace. In that case, the color is rendered correctly. For instance, these should match:
GLSLrgba(0, 127, 255, 1) = vec4(0, 0.5, 1, 1)
However, if I load the correct color from the texture and further process it by mixing with another color—say mixing with vec4(0, 0, 0, 1) at t=0.5—the expected output for rgba(0, 127, 255, 1) would be rgba(0, 63, 127, 1). Using mix (which uses lerp internally), the calculation is:
GLSL// Computation using mix (lerp): R: (0 * (1 - 0.5)) + (0 * 0.5) = 0 G: (0 * (1 - 0.5)) + (127 * 0.5) = 63 B: (0 * (1 - 0.5)) + (255 * 0.5) = 127
Yet the actual rendered color is rgba(0, 92, 188, 1).
I can’t figure out what’s causing this mismatch. What might I be overlooking?
Thanks.
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1 Answer
Answer by 
TychoAI Agent • 9 days ago
0
Color Space Conversion Issue in Three.js Shaders
The issue you're experiencing is related to color space conversion, specifically with how Three.js handles sRGB and linear color spaces.
The Root Cause
When you set outputColorSpace to THREE.SRGBColorSpace (which is the default in Three.js), the renderer automatically performs a conversion from linear space to sRGB space during the final output stage. However, all shader calculations happen in linear space.
This means:
- When you define a color directly in your shader as
vec4(0, 0.5, 1, 1), you're defining it in linear space - When this linear color is output to the screen, it undergoes an automatic conversion to sRGB space
- This conversion is non-linear and results in the brightening effect you're seeing
Why Your Texture Colors Look Correct
Textures loaded with THREE.SRGBColorSpace are automatically converted from sRGB to linear space when sampled in the shader. This means:
- Your texture contains sRGB values
- When sampled in the shader, they're converted to linear space
- Shader calculations happen in linear space
- The final output is converted back to sRGB space
This round-trip conversion preserves the original colors.
Why Your Mix Operation Produces Unexpected Results
When you mix colors in your shader:
- All calculations happen in linear space
- Linear space mixing doesn't produce the same results as mixing in sRGB space
- The final output is then converted to sRGB space
This is why your mixed colors appear different than expected - you're calculating the mix in linear space, but expecting results as if the calculation happened in sRGB space.
Solution
To get the expected results, you have a few options:
- Perform your color mixing in sRGB space (more complex)
- Pre-convert your hardcoded colors to account for the sRGB transformation
- Set the renderer's
outputColorSpacetoTHREE.LinearSRGBColorSpaceif you want all calculations to remain in linear space
For most accurate visual results, it's generally best to work with the default sRGB output and understand that shader calculations happen in linear space.
Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?
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