How can I access and manipulate pixel data within an HTML Canvas for image processing?

Read Pixel Data from HTML Canvas

Querying an HTML Canvas to obtain color information at specific coordinates is a valuable technique for image processing and pixel manipulation. The W3C documentation provides a comprehensive section on pixel manipulation, empowering developers with the means to retrieve and modify pixel data.

To illustrate this concept, let's consider the following example:

Invert an Image Using Pixel Manipulation

Using the getImageData() method, we can retrieve the CanvasPixelArray from the desired coordinates and dimensions. This array contains the color component data for each pixel in the selected region.

<code class="javascript">var context = document.getElementById('myCanvas').getContext('2d');

// Get the ImageData from the specified coordinates and dimensions.
var imgd = context.getImageData(x, y, width, height);
var pix = imgd.data;

// Iterate through each pixel, inverting the color components.
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)
}

// Update the Canvas with the modified ImageData.
context.putImageData(imgd, x, y);</code>

By leveraging pixel manipulation techniques, we can perform a variety of image processing operations, such as color inversion, image blending, and more, empowering developers with a versatile tool for graphical applications.

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