tiff/src/horizontal_differencing.ts

TIFF image decoder written entirely in JavaScript

// Section 14: Differencing Predictor (p. 64)

export function applyHorizontalDifferencing8Bit(
  data: Uint8Array,
  width: number,
  components: number,
): void {
  let i = 0;
  while (i < data.length) {
    for (let j = components; j < width * components; j += components) {
      for (let k = 0; k < components; k++) {
        data[i + j + k] =
          (data[i + j + k] + data[i + j - (components - k)]) & 255;
      }
    }
    i += width * components;
  }
}

export function applyHorizontalDifferencing16Bit(
  data: Uint16Array,
  width: number,
  components: number,
): void {
  let i = 0;
  while (i < data.length) {
    for (let j = components; j < width * components; j += components) {
      for (let k = 0; k < components; k++) {
        data[i + j + k] =
          (data[i + j + k] + data[i + j - (components - k)]) & 65535;
      }
    }
    i += width * components;
  }
}