Question

I’m trying to write a greasemonkey script, and it would be preferable for it to be able to work with images (specifically, find the darkest pixel in an image). Is there a way to do this or must I embed flash?

Answer 1

Since it’s Firefox specific, you can use a canvas element. I’ve never written a greasemonkey script, so I don’t know exactly how you would do it, but the idea is, you create a new canvas element and draw the image onto the canvas. Then, you can get the pixel values from the canvas.

// Create the canvas element var canvas = document.createElement('canvas'); canvas.width = image.width; canvas.height = image.height;  // Draw the image onto the canvas var ctx = canvas.getContext('2d'); ctx.drawImage(image, 0, 0);  // Get the pixel data var imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);  // Loop through imageData.data - an array with 4 values per pixel: red, green, blue, and alpha for (int x = 0; x < imageData.width; x++) {     for (int y = 0; y < imageData.height; y++) {         var index = 4 * (y * imageData.width + x);         var r = imageData.data[index];         var g = imageData.data[index + 1];         var b = imageData.data[index + 2];         var a = imageData.data[index + 3];          // Do whatever you need to do with the rgba values     } }