Question

Is it possible to query a HTML Canvas object to get the color at a specific location?

Answer 1

There’s a section about pixel manipulation in the W3C documentation.

Here’s an example on how to invert an image:

var context = document.getElementById('myCanvas').getContext('2d');  // Get the CanvasPixelArray from the given coordinates and dimensions. var imgd = context.getImageData(x, y, width, height); var pix = imgd.data;  // Loop over each pixel and invert the color. for (var i = 0, n = pix.length; i < n; i += 4) {     pix[i  ] = 255 - pix[i  ]; // red     pix[i+1] = 255 - pix[i+1]; // green     pix[i+2] = 255 - pix[i+2]; // blue     // i+3 is alpha (the fourth element) }  // Draw the ImageData at the given (x,y) coordinates. context.putImageData(imgd, x, y);