fv/lib/filters/remove_red.js

FormVision is a node.js library for extracting data from scanned forms

// Generated by CoffeeScript 2.3.1
var filterBackground;

filterBackground = require('./filter_background');

// Remove red tones from given *image* and return the result (grayscale).
module.exports = function(image) {
  var cyan, desaturatedMask, foreground, formMask, hsv, nearInkMask, red, redMask;
  // Compute desaturated weak text with guessed font-size.
  hsv = filterBackground(image, 25, 35).toHSV();
  // Select 11x11 area around all groups of at least 3 connected gray pixels.
  nearInkMask = hsv.inRange(0, 0, 0, 255, 10, 0.9 * 255).dilate(9, 11).erode(11, 11).dilate(11, 11).toGray();
  desaturatedMask = hsv.inRange(0, 0, 0, 239, 0.3 * 255, 0.9 * 255);
  // Select desaturated pixels with a high probability to be ink.
  desaturatedMask = desaturatedMask.toGray().convolve(2, 2).invert().subtract(nearInkMask);
  // Compute preprinted form (saturated red color).
  red = image.toGray(1, 0, 0);
  cyan = image.toGray(0, 0.5, 0.5);
  redMask = red.subtract(cyan).convolve(1, 1);
  // Remove red and preserve desaturated colors.
  formMask = redMask.add(redMask).subtract(desaturatedMask);
  foreground = image.toGray().add(formMask);
  return foreground;
};