blendSubtract: Additive Threshold Clamping Mode

Unity-Based Threshold Function for High-Luminance Extraction

The subtract blend mode applies an additive threshold operation where color values persist only when the combined luminance exceeds unity. This creates high-contrast selections based on luminance accumulation.

The mathematical definition uses threshold clamping:

$$\text{subtract}(base, blend) = \max(base + blend - 1, 0)$$

Values below the unity threshold are eliminated, while excess luminance above 1.0 creates the final result. This produces stark binary separations between preserved and eliminated regions.

ライブエディター

const fragment = () => {
      const baseGrad = vec3(uv.x, uv.x.mul(0.7), uv.x.mul(0.4))
      const blendGrad = vec3(uv.y.mul(0.6), uv.y, uv.y.mul(0.8))
      const subtracted = blendSubtractVec3(baseGrad, blendGrad)
      const amplified = subtracted.mul(4)
      return vec4(amplified, 1)
}