Step by Step solution about How to resolve the algorithm Percentage difference between images step by step in the JavaScript programming language

Overview: This JavaScript code defines two functions, getImageData and compare, to compare the similarity between two images using pixel-by-pixel difference analysis.

Function 1: getImageData

• Input: An image URL and a callback function.
• Process:
  • Creates an image (img) and canvas (canvas) elements.
  • When the image loads, the canvas size is set to match the image's size, and the image is drawn onto the canvas.
  • The getImageData method is used to retrieve pixel data from the canvas.
  • The callback function is invoked with the extracted pixel data.

Function 2: compare

• Input: URLs of two images and a callback function.
• Process:
  • Calls getImageData for the first image to get its pixel data.
  • Calls getImageData for the second image to get its pixel data.
  • Checks if the two images have different sizes, and if so, returns NaN to indicate they're not comparable.
  • Initializes a diff variable to 0.
  • Iterates over the pixel data of both images, comparing the Red, Green, and Blue components of each pixel.
  • Calculates the absolute difference between the corresponding pixel components and accumulates the difference in the diff variable.
  • Normalizes the difference by dividing it by the total number of pixels and the maximum possible difference value (255).
  • Invokes the callback function with the percentage of pixel difference between the two images.

Usage: In the provided code, compare is called with the URLs of two images ('Lenna50.jpg' and 'Lenna100.jpg'), and a callback function that logs the result. The result represents the percentage of pixel difference between the two images, providing a quantitative measure of their similarity.

function getImageData(url, callback) {
	var img = document.createElement('img');
	var canvas = document.createElement('canvas');

	img.onload = function () {
		canvas.width = img.width;
		canvas.height = img.height;
		var ctx = canvas.getContext('2d');
		ctx.drawImage(img, 0, 0);
		callback(ctx.getImageData(0, 0, img.width, img.height));
	};

	img.src = url;
}

function compare(firstImage, secondImage, callback) {
	getImageData(firstImage, function (img1) {
		getImageData(secondImage, function (img2) {
			if (img1.width !== img2.width || img1.height != img2.height) {
				callback(NaN);
				return;
			}

			var diff = 0;
			
			for (var i = 0; i < img1.data.length / 4; i++) {
				diff += Math.abs(img1.data[4 * i + 0] - img2.data[4 * i + 0]) / 255;
				diff += Math.abs(img1.data[4 * i + 1] - img2.data[4 * i + 1]) / 255;
				diff += Math.abs(img1.data[4 * i + 2] - img2.data[4 * i + 2]) / 255;
			}

			callback(100 * diff / (img1.width * img1.height * 3));
		});
	});
}

compare('Lenna50.jpg', 'Lenna100.jpg', function (result) {
	console.log(result);
});