Canvas - Change colors of an image using HTML5/CSS/JS?

Question

Is there a way to change colors of an image much like in Flash/ActionScript with using only HTML5/CSS/JavaScript?

Here's an example in Flash: http://www.kirupa.com/developer/actionscript/color.htm EDIT: This is the process I wish to duplicate.

I'm trying to accomplish something like this (color changing aspect, preserving lighting and shadows): http://www.acura.com/ExteriorColor.aspx?model=TL WITHOUT loading & replacing a new image each time; I want to be able to simply change the color tone (i.e. do a pure HTML5/CSS/JS method). EDIT: This is the result I wish to achieve, not the process.

Basically I want to change the palette/tone of an image, while preserving the other aspects of the image (such as gradient, lighting, etc.). I have gotten close, but not close enough; I've gotten to the point where I use an image mask and composite that over the original image (sort of like a transparent image overlay). Below is some sample code (please note this is just a snippet, so it may or may not work; I am only displaying sample code so you get an idea of what I'm trying to do):

<div id='mask'>
    <canvas id='canvas' width='100' height='100'></canvas>
</div>
<button data-rgba='255,0,0,0.5'>red</button>
<button data-rgba='0,255,0,0.5'>green</button>

<script>
foo = {};
foo.ctx = jQuery('#canvas')[0];
foo.ctx_context = foo.ctx.getContext('2d');
foo.mask = jQuery('#mask')[0];
foo.img = new Image();
foo.img_path = '/path/to/image_mask.png'; // 100px x 100px image

foo.changeColor = function(rgba){
    foo.ctx_context.clearRect(0, 0, 100, 100);
    foo.ctx_context.fillStyle = 'rgba(' + rgba + ')';
    foo.ctx_context.fillRect(0, 0, 100, 100);
    foo.ctx_context.globalCompositeOperation = 'destination-atop';
    foo.ctx_context.drawImage(foo.img, 0, 0);
    foo.ctx_context.css({'background-image': "url(" + foo.ctx.toDataURL("image/png") + ")"});
};

jQuery("button").click(function(){
    foo.changeColor(jQuery(this).attr('data-rgba'));
});
</script>

The major problem with using this approach is that the images look really flat. There's something else missing, or the mask I'm using (which is a solid white irregular shaped image), is the wrong approach.

Answer 1

This function requires the image to be loaded and it has to be from the same domain (due to cross domain policy)

function tintImage(imgElement,tintColor) {
    // create hidden canvas (using image dimensions)
    var canvas = document.createElement("canvas");
    canvas.width = imgElement.offsetWidth;
    canvas.height = imgElement.offsetHeight;

    var ctx = canvas.getContext("2d");
    ctx.drawImage(imgElement,0,0);

    var map = ctx.getImageData(0,0,320,240);
    var imdata = map.data;

    // convert image to grayscale
    var r,g,b,avg;
    for(var p = 0, len = imdata.length; p < len; p+=4) {
        r = imdata[p]
        g = imdata[p+1];
        b = imdata[p+2];
        // alpha channel (p+3) is ignored           

        avg = Math.floor((r+g+b)/3);

        imdata[p] = imdata[p+1] = imdata[p+2] = avg;
    }

    ctx.putImageData(map,0,0);

    // overlay filled rectangle using lighter composition
    ctx.globalCompositeOperation = "lighter";
    ctx.globalAlpha = 0.5;
    ctx.fillStyle=tintColor;
    ctx.fillRect(0,0,canvas.width,canvas.height);

    // replace image source with canvas data
    imgElement.src = canvas.toDataURL();
}

Assuming your markup looks like this:

<img id='myimage' src='image.jpg'/>

You could use it by calling it with the following parameters:

tintImage(
    document.getElementById('myImage'),
    "#550000" // for a redish tint
);

Working example here: http://jsfiddle.net/pHwmL/1/

Answer 2

Sure, you can get the pixel data, and do HSV adjustments on it. The method you want is getImageData (which returns a UInt8Array, not a normal js array).

There's a nice writeup here which should get you started. You can layer transparent canvas elements on top of each other, which should help avoiding problems with adjusting base components (in your car example, the tyres, windows etc).