Function noisePng

packages/agent-core/test/tools/image-compress.test.ts:65–77

High-entropy image whose PNG barely compresses — used to force the ladder.

(width: number, height: number, alpha = false)

/** High-entropy image whose PNG barely compresses — used to force the ladder. */
async function noisePng(width: number, height: number, alpha = false): Promise<Uint8Array> {
  const image = new Jimp({ width, height, color: 0x000000ff });
  const data = image.bitmap.data;
  for (let i = 0; i < data.length; i += 4) {
    // Deterministic pseudo-random bytes (no Math.random for stable fixtures).
    // Distinct multipliers per channel keep entropy high so PNG barely shrinks.
    data[i] = (i * 2_654_435_761) & 0xff;
    data[i + 1] = (i * 40_503) & 0xff;
    data[i + 2] = (i * 12_289) & 0xff;
    data[i + 3] = alpha ? (i * 7 + 17) & 0xff : 0xff;
  }
  return new Uint8Array(await image.getBuffer('image/png'));
}

async function decodeAlpha(bytes: Uint8Array): Promise<boolean> {
  const image = await Jimp.fromBuffer(Buffer.from(bytes));