<canvas> ... </canvas>tags can be used as a fallback for browsers which don't support canvas rendering. It's also very useful for assistive technology users (like screen readers) which can read and interpret the sub DOM in it. A good example at html5accessibility.com demonstrates how this can be done:
ImageDataobject represents the underlying pixel data of an area of a canvas object. It contains the following read-only attributes:
ImageDatainterface represents the underlying pixel data of an area of a
<canvas>element. It is created using the
ImageData()constructor or creator methods on the
CanvasRenderingContext2Dobject associated with a canvas:
getImageData(). It can also be used to set a part of the canvas by using
<canvas>looks like the
<img>element, with the only clear difference being that it doesn't have the
altattributes. Indeed, the
<canvas>element has only two attributes,
height. These are both optional and can also be set using DOM properties. When no
heightattributes are specified, the canvas will initially be 300 pixels wide and 150 pixels high. The element can be sized arbitrarily by CSS, but during rendering the image is scaled to fit its layout size: if the CSS sizing doesn't respect the ratio of the initial canvas, it will appear distorted.
CanvasPatterninterface represents an opaque object describing a pattern, based on an image, a canvas or a video, created by the
HTMLCanvasElement.getContext()method returns a drawing context on the canvas, or
nullif the context identifier is not supported.
HTMLCanvasElement.toBlob()method creates a
Blobobject representing the image contained in the canvas; this file may be cached on the disk or stored in memory at the discretion of the user agent. If
typeis not specified, the image type is
image/png. The created image is in a resolution of 96dpi.
image/jpegimages to specify the quality of the output.
ImageBitmapinterface represents a bitmap image which can be drawn to a
<canvas>without undue latency. It can be created from a variety of source objects using the
ImageBitmapprovides an asynchronous and resource efficient pathway to prepare textures for rendering in WebGL.