image-js/lib/util/histogram.js

Image processing and manipulation in JavaScript

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.mean = mean;
exports.median = median;
/**
 * Returns the median of an histogram
 * @param {number[]} histogram
 * @return {number}
 * @private
 */
function median(histogram) {
  let total = histogram.reduce((sum, x) => sum + x);
  if (total === 0) {
    throw new Error('unreachable');
  }
  let position = 0;
  let currentTotal = 0;
  let middle = total / 2;
  let previous;
  while (true) {
    if (histogram[position] > 0) {
      if (previous !== undefined) {
        return (previous + position) / 2;
      }
      currentTotal += histogram[position];
      if (currentTotal > middle) {
        return position;
      } else if (currentTotal === middle) {
        previous = position;
      }
    }
    position++;
  }
}

/**
 * Retuns the mean of an histogram
 * @param {number[]} histogram
 * @return {number}
 * @private
 */
function mean(histogram) {
  let total = 0;
  let sum = 0;
  for (let i = 0; i < histogram.length; i++) {
    total += histogram[i];
    sum += histogram[i] * i;
  }
  if (total === 0) {
    return 0;
  }
  return sum / total;
}