OffscreenCanvas.convertToBlob()
Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
The OffscreenCanvas.convertToBlob()
method creates a Blob
object representing the image contained in the canvas.
The desired file format and image quality may be specified.
If the file format is not specified, or if the given format is not supported, then the data will be exported as image/png
.
Browsers are required to support image/png
; many will support additional formats including image/jpg
and image/webp
.
The created image will have a resolution of 96dpi for file formats that support encoding resolution metadata.
Syntax
convertToBlob()
convertToBlob(options)
Parameters
options
Optional-
An object with the following properties:
type
-
A string indicating the image format. The default type is
image/png
; this image format will be also used if the specified type is not supported. quality
-
A
Number
between0
and1
indicating the image quality to be used when creating images using file formats that support lossy compression (such asimage/jpeg
orimage/webp
). A user agent will use its default quality value if this option is not specified, or if the number is outside the allowed range.
Return value
Exceptions
The promise may be rejected with the following exceptions:
InvalidStateError
DOMException
-
The
OffscreenCanvas
is not detached; in other words it still associated with the DOM and not the current worker. SecurityError
DOMException
-
The canvas context mode is 2d and the bitmap is not origin-clean; at least some of its contents have or may have been loaded from a site other than the one from which the document itself was loaded.
IndexSizeError
DOMException
-
The canvas bitmap has no pixels (either the horizontal or vertical dimension is zero).
EncodingError
DOMException
-
The blob could not be created due to an encoding error.
Examples
const offscreen = new OffscreenCanvas(256, 256);
const gl = offscreen.getContext("webgl");
// ... some drawing using the gl context ...
offscreen.convertToBlob().then( blob => console.log(blob));
// Blob { size: 334, type: "image/png" }
Specifications
Specification |
---|
HTML Standard # dom-offscreencanvas-converttoblob-dev |
Browser compatibility
BCD tables only load in the browser
See also
- The interface defining this method,
OffscreenCanvas
.