canvas-to-buffer

A tiny converter to turn any graphic canvas into a buffer. With focus on speed: it doesn't create an expensive copy and makes clever use of atob() and Uint8Array.

Following performance tests prove that this module is using the fastest known method: Data URI to Buffer performance tests

Useful scenarios for this module:

Pipe each canvas from the browser to the server through web sockets at light speed
Compress a canvas into binary form for persistence
If the Canvas package is too heavy for you and you only need the toBuffer part and/or you care about speed
Have one package that works on both sides, browser and server. In other words: you can browserify it.

Furthermore this module is an important part of the Videomail Client whose implementation can be seen on Videomail

Example

// I call it a Frame but you can go with i.E. CanvasConverter, whatever
var Frame = require("canvas-to-buffer");

// Drop in any canvas, i.E. from a webcam
var frame = new Frame(canvas);

// Automatically detects image type and does the conversion
var buffer = frame.toBuffer();

// Returns the chosen image type, could be `'image/png'`
var imageType = frame.getImageType();

Options (example)

var Frame = require("canvas-to-buffer");
var frame = new Frame(canvas, {
  quality: 0.4,
  image: {
    types: ["webp", "png"],
  },
});

The example means, it tries to encode the canvas first as webp at the given quality before converting that data into a buffer. If that fails, i.E. the browser does not support it, then it will try again with the png format.

quality

Default: 0.5

Determines the quality when encoding the canvas into an image with the given type.

image.types

Default: ['webp', 'jpeg']

You know, turning a canvas into binary form requires an image type. No worries this module is able to automatically detect the supported image type in your browser.

But if you want to explicitly specify the image type for whatever reason, this is the option to use.

It can be a string or an array with max two image types.

FYI webp images have better compression, but are supported on Google Chrome only. Hence this module automatically falls back to 'jpeg' for any other browsers. Beware that binary data for JPEGs is about 20% larger.

Public functions

Just toBuffer() and getImageType(). Pretty self-explanatory.

But both need a callback when you use this package on the server side, see next chapter.

Compatibility

This package works on both sides, browser or server. For browser environments everything happens in sync, whereas on the server side it's in async and hence callbacks are needed in all public functions.

Tests

Tests can be run on your machine but you'll have to install Cairo first, see: How to install Cairo on different environments?

scris / canvas-to-buffer