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Pure Javascript HTML5 (Ca)nvas (Man)ipulation

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About the Project

The main focus of CamanJS is manipulating images using the HTML5 canvas and Javascript. It's a combination of a simple-to-use interface with advanced and efficient image/canvas editing techniques. It is also completely library independent and can be safely used next to jQuery, YUI, Scriptaculous, MooTools, etc.

CamanJS is very easy to extend with new filters and plugins, and it comes with a wide array of image editing functionality, which is only growing as the community makes more plugins.

For more information, I highly recommend taking a look at the official website where there is more comprehensive documentation and interactive demos.

NodeJS Compatibility

There is now a version of CamanJS that is made to work with NodeJS. It has all of the functionality of the normal browser version, including plugins. Take a look at the node branch for more information.

Block Renderer

CamanJS now uses a block rendering system, which gives some notable benefits:

  • Image rendering is now asynchronous, which means page rendering is no longer blocked.
  • Slower filters get a nice speed improvement due to (fake) render concurrency.

The way the renderer works is:

  1. When each filter function is called, instead of rendering immediately, they are added to a render queue.
  2. When the render() function is called, THEN the rendering actually begins.
  3. The next filter is shifted off of the render queue and sent to the rendering function.
  4. The image is divided into X number of blocks, which are simply horizontal partitions in the image.
  5. The filter is performed on each block simultaneously by using setTimeout() with a 0ms timeout value. Using setTimeout() is what forces each block to render asynchronously, even if the timeout value is 0.
  6. When a block is finished being rendered, it calls a function that tracks the # of blocks that have finished. When all blocks have finished, it signals that the filter is finished rendering.
  7. If there are more filters in the render queue, then steps 3-6 happen for each until the queue empties.
  8. When the queue empties, the callback supplied to render() is called.

The concurrency defaults to 4 blocks, but you can change this to whatever number you want by changing the Caman global variable renderBlocks:

Caman.renderBlocks = 8; // even number recommended

How to Use

Building CamanJS Yourself

CamanJS is built into the dist folder. The copies of CamanJS that are already in the folder are kept up-to-date; however, if you make any modifications to CamanJS and wish to combine all of the plugins and minify the code, you will have to re-build it yourself. Building CamanJS also runs JSHint on the code to check for syntax and formatting errors, which are reported at build time.

Building CamanJS requires NodeJS to be installed. To build, simply run:

node Makefile.js

The copies of CamanJS that are in the dist folder will be overwritten with the newly built copies. The 'full' copies include all of the plugins, while the non-full copies are simply the core library.

Basic Usage

Using CamanJS is simple. It goes something like this:

Caman('path/to/image.jpg', '#canvas-id', function () {
  // and so on...

You can also directly point to an image if you don't want to create a separate canvas element. In this case, the image element will be replaced with the canvas element, and the canvas will be drawn with the image content:

Caman("#image-id", function () {

You can now even save images after they've been modified! With the current implementation, users will have to rename the file to something.(png|jpg) since they get redirected to the base64 encoding of the image and the browser doesn't know the file type. The save() function defaults to png, but you can override this and specify either png or jpg.

Caman('img/example.jpg', '#image-caman', function () {
  this.render(function () {'png'); // shows a download file prompt

    // or...
    this.toBase64(); //  base64 data URL representation of the image. useful if you want to upload the modified image.

CamanJS Layering System

CamanJS now supports a powerful layering system, much like the one you would find in Photoshop or GIMP. Here's an example of how it works:

Caman('#test', function () {
   * Creates a new layer. Everything called inside the callback argument will be applied
   * to the new layer. Layers have some special layer-only functions such as setBlendingMode(),
   * opacity(), and copyParent(). In order to access the standard filters, you need to access them
   * through this.filter.
  this.newLayer(function () {
    // There are many blending modes, more below.
     * Yep, you can stack multiple layers! The further a layer is nested, the higher up on the layer
     * stack it will be.
    this.newLayer(function () {

Layer Blending Modes

These are all of the layer blending modes currently supported by CamanJS. You can also add new blending modes via plugins if you need some special functionality.

  • normal
  • multiply
  • screen
  • overlay
  • difference
  • addition
  • exclusion
  • softLight

If you wish to add your own blending mode:

(function (Caman) {

// Extend this blenders object
Caman.extend(Caman.manip.blenders, {
     * This function will be iterated over in a pixel-by-pixel fashion.
     * Both arguments are rgba objects:
     *      rgbaLayer.r, rgbaLayer.g, rgbaLayer.b
     * The first argument is the current pixel from the layer, and the second
     * argument is the current pixel from the parent canvas (the canvas below
     * the current layer).
    someBlender: function (rgbaLayer, rgbaParent) {
        rgbaParent.r = rgbaLayer.r * 2 - rgbaParent.r;
        rgbaParent.g = rgbaLayer.g * 1.5 - rgbaParent.g;
        rgbaParent.b = rgbaLayer.b * 2.5 - rgbaParent.b;
        // Important! Remember to return the updated rgba object!
        return rgbaParent;


Editing Remote Images

CamanJS can even edit images that are stored remotely. Since the browser enforces a same-origin policy for editing canvas data, we have to load the image data via a local proxy.

CamanJS comes with a PHP proxy (you're welcome to add a proxy in the language of your choice) that you can use in the proxies folder. Before you use CamanJS for editing, all you have to do to enable the proxy is:

// Will use the PHP proxy in the proxies folder. You can also specify a URL instead of calling useProxy().
Caman.remoteProxy = Caman.useProxy('php');

If no proxy is defined when a remote image is attempted to be edited, an error will be thrown.

Caman Events

Currently CamanJS has three different events you can listen for, and it is very simple to add new events if you need to.

  • processStart
    • fired when a single image filter begins manipulating an image
  • processComplete
    • fired when a single image filter finishes manipulating an image
  • renderFinished
    • fired when all image filters are done and an image is finished being rendered

You may also find this extremely handy:

Caman('img/example.jpg', '#image-caman', function () {
  this.colorize('#AF3D15', 25);
  // Callback to render() fires when this image is done rendering.
  this.render(function () {
    console.log("Image finished rendering!");

How to Extend

Extending CamanJS is easy as well. It's accomplished by adding functions onto the manip object. Below is a simple example of how to do so:

(function (Caman) {
  // Pixel-wise manipulation
  Caman.manip.fancy_filter = function (adjust) {
    // === IMPORTANT ===
    // this.process() will be run in a loop, and the
    // rgba object represents the current pixel's rgba
    // values. you *must* return the modified rgba object
    // for it to work properly and you *must* name the function
    // passed in the 2nd argument to process() the same name as
    // this filter.
    return this.process(adjust, function fancy_filter(rgba) {
      rgba.r += adjust;
      rgba.g -= adjust;
      rgba.b += adjust * 2;
      rgba.a = 0.9;
      // to get data about a pixel relative to this one currently
      // being processed, you can use getPixel([horiz_offset], [vert_offset]);
      var topLeft      = this.getPixelRelative(-1, 1);
      var topRight    = this.getPixelRelative(1, 1);
      var bottomLeft  = this.getPixelRelative(-1, -1);
      var bottomRight  = this.getPixelRelative(1, -1);
      // gets a pixel from the canvas at the specified absolute coordinates
      var absPixel    = this.getPixel(200, 300);
      return rgba;
    // If you want to use a convolution kernel instead of manipulating each
    // pixel directly, you can easily do it like this:
    Caman.manip.convolutionFilter = function () {
      return this.processKernel('Convolution Filter', [
        [1, 1, 1],
        [1, 1, 1],
        [1, 1, 1]
      ], 9);

The arguments to processKernel are:

this.processKernel( Filter Name, Convolution Matrix (3x3 or 5x5), [Divisor], [Bias] );

Utility Functions

CamanJS comes with a set of utility functions that you may find very useful when extending it. In the main body of the function thats extending CamanJS, you can simply access them through Caman, e.g. Caman.rgb_to_hsl(). Their names should be pretty self explanatory:

  • rgb_to_hsl()
  • hsl_to_rgb()
  • rgb_to_hsv()
  • hsv_to_rgb()
  • rgb_to_xyz()
  • xyz_to_rgb()
  • xyz_to_lab()
  • lab_to_xyz()
  • hex_to_rgb()


CamanJS has both QUnit unit testing and a custom benchmarking page to monitor render times on a per-filter basis. Simply open test/index.html for the QUnit tests, and test/benchmark.html for the benchmarking tests.

If you add a filter, please edit test/benchmark/benchmark.js and add your filter (with appropriate args) to the list at the top of the file.

Project To-do

  • Implement a way to specify canvas elements by class instead of id, and apply effects to all found canvases.
  • Add lots more adjustments/effects

Project Contributors

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