support more diffing methods

Author: mouafa

lib/diff.js

@@ -1,5 +1,4 @@
-const { rgb2yiqDistance } = require('./YIQ')
-const { rgbDistance } = require('./RGB')
+const methods = require('./methods')
 const { highlight, blendAlpha } = require('./util')
 const log = require('./log')
 
@@ -8,11 +7,13 @@ const defaultOptions = {
   highlightFade: true,
   highlightColor: [255, 0, 0],
   transparent: false,
-  overlapse: false
+  overlapse: false,
+  method: 'rgb'
 }
 
 function diff(img1Buffer, img2Buffer, option = {}) {
   option = Object.assign({}, defaultOptions, option)
+  const method = methods[option.method] ? methods[option.method] : methods[defaultOptions.method]
 
   const out = {
     data: Buffer.from(img1Buffer)
@@ -25,7 +26,7 @@ function diff(img1Buffer, img2Buffer, option = {}) {
   for (let i = 0; i < length; i = i + 4) {
     pixel1 = [img1Buffer[i], img1Buffer[i + 1], img1Buffer[i + 2]]
     pixel2 = [img2Buffer[i], img2Buffer[i + 1], img2Buffer[i + 2]]
-    const distance = rgbDistance(pixel1, pixel2)
+    const distance = method(pixel1, pixel2)
 
     if (distance > option.threshold) {
       diffPixels++

testdrive/index.js

@@ -13,6 +13,11 @@ diff('./fixture/img1.png', './fixture/img2.png', './fixture/diff_solid.png', { h
 diff('./fixture/img1.png', './fixture/img2.png', './fixture/diff_transparent.png', { transparent: true, highlightFade: false })
 diff('./fixture/img1.png', './fixture/img2.png', './fixture/diff_overlapse.png', { overlapse: true, transparent: true })
 
+diff('./fixture/img1.png', './fixture/img2.png', './fixture/diff_method_rgb.png', { method: 'rgb', highlightFade: false })
+diff('./fixture/img1.png', './fixture/img2.png', './fixture/diff_method_rgbTuned.png', { method: 'rgbTuned', highlightFade: false })
+diff('./fixture/img1.png', './fixture/img2.png', './fixture/diff_method_yiq.png', { method: 'yiq', highlightFade: false })
+diff('./fixture/img1.png', './fixture/img2.png', './fixture/diff_method_yiqTuned.png', { method: 'yiqTuned', highlightFade: false })
+
 function diff(inputImg1, inputImg2, outputImg, options = {}) {
   var img1 = fs
     .createReadStream(inputImg1)