image-js/lib/image/transform/mask/intermodes.js

Image processing and manipulation in JavaScript

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = intermodes;
/*
 *
 * see https://github.com/fiji/Auto_Threshold/blob/master/src/main/java/fiji/threshold/Auto_Threshold.java
 * Intermodes: This assumes a bimodal histogram. Implements the thresholding Prewitt, JMS & Mendelsohn, ML (1966),
 * "The analysis of cell images", Annals of the NewYork Academy of Sciences 128: 1035-1053
 *
 */

function intermodes(histogram) {
  let iHisto = histogram.slice();
  let iter = 0;
  while (!bimodalTest(iHisto)) {
    // smooth with a 3 point running mean filter
    let previous = 0;
    let current = 0;
    let next = iHisto[0];
    for (let i = 0; i < histogram.length - 1; i++) {
      previous = current;
      current = next;
      next = iHisto[i + 1];
      iHisto[i] = (previous + current + next) / 3;
    }
    iHisto[histogram.length - 1] = (current + next) / 3;
    iter++;
    if (iter > 10000) {
      throw new Error('Intermodes Threshold not found after 10000 iterations');
    }
  }

  // The threshold is the mean between the two peaks.
  let tt = 0;
  for (let i = 1; i < histogram.length - 1; i++) {
    if (iHisto[i - 1] < iHisto[i] && iHisto[i + 1] < iHisto[i]) {
      tt += i;
    }
  }
  return Math.floor(tt / 2.0);
}
function bimodalTest(iHisto) {
  let b = false;
  let modes = 0;
  for (let k = 1; k < iHisto.length - 1; k++) {
    if (iHisto[k - 1] < iHisto[k] && iHisto[k + 1] < iHisto[k]) {
      modes++;
      if (modes > 2) {
        return false;
      }
    }
  }
  if (modes === 2) {
    b = true;
  }
  return b;
}