Created
August 8, 2016 15:04
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Image diffing using JavaScript
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const avgDiff = (canvas) => { | |
let context = canvas.getContext('2d'); | |
let imageData = context.getImageData(0, 0, canvas.width, canvas.height); | |
let data = imageData.data; | |
let sum = 0; | |
let count = 0; | |
// TODO: perhaps this can be sped up by not going over every pixel? | |
for (let i = 0; i < data.length; i += 4) { | |
sum += Math.abs(128 - data[i]); // red | |
sum += Math.abs(128 - data[i + 1]); // green | |
sum += Math.abs(128 - data[i + 2]); // blue | |
// skipping alpha | |
count += 3; | |
} | |
return sum / count; | |
}; | |
const invert = (canvas) => { | |
let context = canvas.getContext('2d'); | |
let imageData = context.getImageData(0, 0, canvas.width, canvas.height); | |
let data = imageData.data; | |
// Invert rgb data | |
for (let i = 0; i < data.length; i += 4) { | |
data[i] = 255 - data[i]; // red | |
data[i + 1] = 255 - data[i + 1]; // green | |
data[i + 2] = 255 - data[i + 2]; // blue | |
// skipping alpha | |
} | |
// Overwrite original image | |
context.putImageData(imageData, 0, 0); | |
}; | |
module.exports = (sources) => { | |
// *** Setup *** | |
let canvas1 = document.createElement('canvas'); | |
let canvas2 = document.createElement('canvas'); | |
// DEBUG | |
// document.body.appendChild(canvas1); | |
// document.body.appendChild(canvas2); | |
let context1 = canvas1.getContext('2d'); | |
let context2 = canvas2.getContext('2d'); | |
let results = []; | |
let promises = []; | |
console.time('diff'); | |
console.info('diffing!'); | |
for (i = 0; i < sources.length - 1; i += 1) { | |
let p1 = new Promise((resolve, reject) => { | |
var image = document.createElement('img'); | |
image.src = sources[i]; | |
image.onload = e => { | |
canvas1.width = image.width; | |
canvas1.height = image.height; | |
context1.drawImage(image, 0, 0); | |
resolve(); | |
}; | |
image.onerror = e => { | |
reject(); | |
}; | |
}); | |
let p2 = new Promise((resolve, reject) => { | |
var image = document.createElement('img'); | |
image.src = sources[i + 1]; | |
image.onload = e => { | |
context2.globalAlpha = 1; // Reset alpha channel | |
canvas2.width = image.width; | |
canvas2.height = image.height; | |
context2.drawImage(image, 0, 0); | |
resolve(); | |
}; | |
image.onerror = e => { | |
reject(); | |
}; | |
}); | |
let p3 = Promise.all([p1, p2]).then(() => { | |
// Invert 1st image | |
invert(canvas1); | |
// Layer 1st image over 2nd image | |
context2.globalAlpha = 0.5; // This value influences shapes/images drawn to the context | |
context2.drawImage(canvas1, 0, 0, canvas1.width, canvas1.height); | |
// Get diff from average | |
results.push(avgDiff(canvas2)); | |
}); | |
promises.push(p3); | |
} | |
return Promise.all(promises).then(() => { | |
console.timeEnd('diff'); | |
console.info('end diff'); | |
return results; | |
}); | |
}; |
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