Equirectangular Projection Color Issues in Three.js

I've reviewed your issue with the equirectangular projection showing darker and more saturated colors compared to the original scene. This is a common problem when working with texture rendering pipelines in Three.js.

Potential Causes

The color discrepancy you're experiencing could be due to several factors:

1. Gamma correction issues: When rendering to a texture and then re-rendering that texture, gamma correction might be applied twice.

2. Shader precision: Your custom shader might be processing colors with different precision than the main renderer.

3. Texture encoding: The texture encoding format might not be preserving the original color values correctly.

Alternative Approaches

Instead of rendering the equirectangular projection to a plane, you could try:

1. Direct Canvas Rendering: Use the WebGLRenderer's readRenderTargetPixels method to read the pixels from your equirectangular render target and draw them directly to a 2D canvas context.

JAVASCRIPTCopied
// After rendering to equirectangularRenderTarget
const width = equirectangularRenderTarget.width;
const height = equirectangularRenderTarget.height;
const buffer = new Uint8Array(width * height * 4);

renderer.readRenderTargetPixels(
  equirectangularRenderTarget,
  0, 0, width, height,
  buffer
);

// Draw to a 2D canvas
const canvas = document.createElement('canvas');
canvas.width = width;
canvas.height = height;
const context = canvas.getContext('2d');
const imageData = context.createImageData(width, height);
imageData.data.set(buffer);
context.putImageData(imageData, 0, 0);

// Now canvas contains your equirectangular image
document.body.appendChild(canvas);

2. Adjust Texture Encoding: Make sure your render target and materials use consistent encoding:

JAVASCRIPTCopied
// Set consistent encoding
equirectangularRenderTarget.texture.encoding = THREE.sRGBEncoding;
planeMaterial.map.encoding = THREE.sRGBEncoding;
renderer.outputEncoding = THREE.sRGBEncoding;

3. Modify Your Shader: If you're using a custom shader, ensure it's handling color space correctly:

GLSLCopied
// In your fragment shader
vec4 texColor = texture2D(map, vUv);
// Convert from linear to sRGB space if needed
texColor.rgb = pow(texColor.rgb, vec3(1.0/2.2));
gl_FragColor = texColor;

Debugging Approach

To isolate the issue, try:

1. Rendering the equirectangular texture directly without any custom shaders
2. Comparing the output with and without gamma correction
3. Testing with a simple color pattern to see if all colors are affected equally

Without seeing your specific shader code, these are general approaches to address the color discrepancy issue in equirectangular projections.