Function analyzeTexture

js/textureAnalysis.js:27–76

(imageData)

const _cache = new WeakMap();

/**
 * @param {ImageData} imageData  RGBA pixel buffer (only the R channel is read)
 * @returns {{ meanGrad: number, sharpFrac: number, pixelsPerEdge: number }}
 */
export function analyzeTexture(imageData) {
  if (!imageData) {
    return { meanGrad: 0, sharpFrac: 0, pixelsPerEdge: 4.0 };
  }
  const cached = _cache.get(imageData);
  if (cached) return cached;

  const { width, height, data } = imageData;
  if (width < 3 || height < 3) {
    const fallback = { meanGrad: 0, sharpFrac: 0, pixelsPerEdge: 4.0 };
    _cache.set(imageData, fallback);
    return fallback;
  }

  const stride = width * 4;
  let sumGrad = 0;
  let sharpCount = 0;
  let pixelCount = 0;

  // Central differences on the red channel; skip the 1-pixel border.
  for (let y = 1; y < height - 1; y++) {
    const rowOff = y * stride;
    for (let x = 1; x < width - 1; x++) {
      const i = rowOff + x * 4;
      const left  = data[i - 4];
      const right = data[i + 4];
      const up    = data[i - stride];
      const down  = data[i + stride];
      const dx = (right - left) * 0.5;
      const dy = (down  - up)   * 0.5;
      const mag = Math.sqrt(dx * dx + dy * dy);
      sumGrad += mag;
      if (mag > SHARP_THRESHOLD) sharpCount++;
      pixelCount++;
    }
  }

  const meanGrad = sumGrad / pixelCount;
  const sharpFrac = sharpCount / pixelCount;

  let pixelsPerEdge;
  if (sharpFrac > 0.15 || meanGrad > 50)      pixelsPerEdge = 1.0;
  else if (sharpFrac > 0.05 || meanGrad > 20) pixelsPerEdge = 1.5;
  else if (meanGrad > 8)                       pixelsPerEdge = 2.5;
  else                                         pixelsPerEdge = 4.0;

  const result = { meanGrad, sharpFrac, pixelsPerEdge };
  _cache.set(imageData, result);