Can You Query Individual Pixel Colors from an HTML Canvas?

Accessing Pixels in HTML Canvas

Can HTML Canvas objects be interrogated to retrieve the color of specific pixels?

Answer:

Yes, you can retrieve individual pixel values from a canvas using the W3C's pixel manipulation methods.

Example:

The example below demonstrates inverting the colors of an image on the canvas:

<code class="javascript">// Obtain the CanvasPixelArray for the specified coordinates and dimensions
var imgd = context.getImageData(x, y, width, height);
var pix = imgd.data;

// Iterate over each pixel and invert its 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)
}

// Display the modified ImageData at the specified (x,y) coordinates
context.putImageData(imgd, x, y);</code>

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