Modality / VOI Lut

lut.js

function modalityLutFunctor(s, i) {
  return (x) => s * x + i;
}

function voiLutFunctor(wc, ww, maxOutput, minOutput) {
  const left = wc - ww / 2;
  const right = wc + ww / 2;
  const a = (maxOutput - minOutput) / (right - left);
  const b = -left * a;
  return (x) => a * x + b;
}

function computeBound(s, i, wc, ww) {
  const left = wc - ww / 2;
  const right = wc + ww / 2;
  return {
    min: (left - i) / s,
    max: (right - i) / s,
  }
}

function computeLut(s, i, wc, ww, maxOutput = 255, minOutput = 0) {
  const modalityLut = modalityLutFunctor(s, i);
  const voiLut = voiLutFunctor(wc, ww, maxOutput, minOutput);
  const { min, max } = computeBound(s, i, wc, ww);
  const lut = [];

  for (let i = min; i < max + 1; ++i) {
    lut[i - min] = Math.round(voiLut(modalityLut(i)));
  }

  return { min, max, lut };
}

computeLut(2, 1, 10, 10);