ImageData: data property - Web APIs | MDN (original) (raw)

Baseline

Widely available

Note: This feature is available in Web Workers.

The readonly ImageData.data property returns aUint8ClampedArray that contains the ImageData object's pixel data. Data is stored as a one-dimensional array in the RGBA order, with integer values between 0 and 255 (inclusive).

Value

Examples

Getting an ImageData object's pixel data

This example creates an ImageData object that is 100 pixels wide and 100 pixels tall, making 10,000 pixels in all. The data array stores four values for each pixel, making 4 x 10,000, or 40,000 values in all.

let imageData = new ImageData(100, 100);
console.log(imageData.data); // Uint8ClampedArray[40000]
console.log(imageData.data.length); // 40000

Filling a blank ImageData object

This example creates and fills a new ImageData object with colorful pixels.

HTML

<canvas id="canvas"></canvas>

JavaScript

Since each pixel consists of four values within the data array, thefor loop iterates by multiples of four. The values associated with each pixel are R (red), G (green), B (blue), and A (alpha), in that order.

const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d");
const imageData = ctx.createImageData(100, 100);

// Fill the array with RGBA values
for (let i = 0; i < imageData.data.length; i += 4) {
  // Percentage in the x direction, times 255
  let x = ((i % 400) / 400) * 255;
  // Percentage in the y direction, times 255
  let y = (Math.ceil(i / 400) / 100) * 255;

  // Modify pixel data
  imageData.data[i + 0] = x; // R value
  imageData.data[i + 1] = y; // G value
  imageData.data[i + 2] = 255 - x; // B value
  imageData.data[i + 3] = 255; // A value
}

// Draw image data to the canvas
ctx.putImageData(imageData, 20, 20);

Result

More examples

Specifications

Browser compatibility

See also