CanvasRenderingContext2D.getImageData()
The CanvasRenderingContext2D
method
getImageData()
of the Canvas 2D API returns an
ImageData
object representing the underlying pixel data for a specified
portion of the canvas.
This method is not affected by the canvas's transformation matrix. If the specified
rectangle extends outside the bounds of the canvas, the pixels outside the canvas are
transparent black in the returned ImageData
object.
Note: Image data can be painted onto a canvas using the
putImageData()
method.
You can find more information about getImageData()
and general
manipulation of canvas contents in Pixel
manipulation with canvas.
Syntax
ctx.getImageData(sx, sy, sw, sh);
Parameters
sx
-
The x-axis coordinate of the top-left corner of the rectangle from which the
ImageData
will be extracted. sy
-
The y-axis coordinate of the top-left corner of the rectangle from which the
ImageData
will be extracted. sw
-
The width of the rectangle from which the
ImageData
will be extracted. Positive values are to the right, and negative to the left. sh
-
The height of the rectangle from which the
ImageData
will be extracted. Positive values are down, and negative are up.
Return value
An ImageData
object containing the image data for the rectangle of the
canvas specified. The coordinates of the rectangle's top-left corner are
(sx, sy)
, while the coordinates of the bottom corner are
(sx + sw, sy + sh)
.
Exceptions
IndexSizeError
DOMException
-
Thrown if either
sw
orsh
are zero. SecurityError
DOMException
-
The canvas contains or may contain pixels which were loaded from an origin other than the one from which the document itself was loaded. To avoid a
SecurityError
DOMException
being thrown in this situation, configure CORS to allow the source image to be used in this way. See Allowing cross-origin use of images and canvas.
Example
Getting image data from a canvas
This example draws a rectangle, and then uses getImageData()
to grab a
portion of the canvas.
<canvas id="canvas"></canvas>
The object retrieved by getImageData()
has a width of 200 and a height of
100, for a total of 20,000 pixels. Of those pixels, most are either transparent or taken
from off the canvas; only 2,500 of them are opaque black (the color of the drawn
rectangle).
const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');
ctx.rect(10, 10, 100, 100);
ctx.fill();
let imageData = ctx.getImageData(60, 60, 200, 100);
ctx.putImageData(imageData, 150, 10);
Result
Specifications
Specification |
---|
HTML Standard # dom-context-2d-getimagedata-dev |
Browser compatibility
BCD tables only load in the browser
See also
- The interface defining this method:
CanvasRenderingContext2D
ImageData
objectCanvasRenderingContext2D.putImageData()
- Pixel manipulation with canvas