Click here to open the tool!

Image error level analysis is a technique that can help to identify manipulations to compressed (JPEG) images by detecting the distribution of error introduced after resaving the image at a specific compression rate. I stumbled across this technique in this presentation by Neal Krawetz and decided to do a quick implementation in JavaScript.

How to use this tool

To analyse an image simply drag and drop it onto the page (requires a modern browser like firefox or chrome). Then play with the quality slider to spot anomalies in the error level. The image I analyzed in the screenshot above is a picture of myself that I modified in GIMP. As you can see the error level on the fake part is quite significantly higher than on the rest of the image. There are no such anomalies on the original.

Having that said the algorithm is not exactly reliable, especially with images that have been rescaled and compressed often/intensely. So take it with a pinch of salt and feel free to have a look at the simple source code.

29a.ch/sandbox/2011/addresscloud/

As some of you know I work for local.ch. I was looking for cool visualizations to do with our data for quite a while, missing the obvious - plotting all our 3.7 million geocoded addresses in 3D using WebGL! I'm actually quite impressed by the accuracy of the data. But go and have a look for your self.

Controls

WASD + Mouse (drag). Velocity is scaled with altitude.

Video

If you can't see the demo for some reason I uploaded a short video of the demo to youtube.

Techniques

The points are encoded in a Float32Array, then sorted and gziped using a python script. Sorting the data improves the compression ratio by over 200% so it's well worth the effort. This brings the original 100mb file down to 7mb.

The file is then loaded using XHR level 2, which supports binary files and progress events. The points are then rendered using WebGL as GL_POINTS and additive blending is used to give it a glow effect. In the future I might add HDR rendering and blooming.

There is no level of detail or culling performed so this will require a relatively powerful rig. Also note that for some reason Firefox Aurora (9) seems to be quicker than Chrome Dev (16) for some mysterious reason. I would expect all of the work to be done by OpenGL so I'm not sure about where this comes from. It could be chromes process isolation.

Sourcecode

You can find the source code on github if you want to get into some hacking. Note that the data belongs to local.ch and may not be used.

View Demo

Some of you might remember my Chaotic Particles demo from last year. That demo was featuring 10'000 particles on a plain old 2d canvas. I decided to optimize that demo a bit in order to support 100'000 particles. I also fixed a little issue where numeric inaccuracy allowed particles to escape and made the influence map more fine grained.

Want to see the source? Just use view source and feel free to ask questions.

Next up: 4'000'000 Particles using WebGL.

View Demo

I think this is my favorite canvas demo I have created so far. It is an interactive drawing tool based on particle effects. It is the result of me trying to create some generative art using canvas. The techniques used are actually pretty similar to the ones shown in my frontendconf talk on particle systems. In short:

p.vx = p.vx*0.8 + getNoise(p.x, p.y, 0)*4+fuzzy(0.1);
p.vy = p.vy*0.8 + getNoise(p.x, p.y, 1)*4+fuzzy(0.1);

p.x += p.vx;
p.y += p.vy;

data[index] = tonemap(hdrdata[index] += r);
data[index+1] = tonemap(hdrdata[index+1] += g);
data[index+2] = tonemap(hdrdata[index+2] += b);

I'm planning to play with a few improvements especially in tone mapping and controls in the future but feel free to take a look at the source on github. I hope you enjoy it.

Video

Video from my talk at frontendconf on particles and html5 canvas, 100% live coding.

Video on ustream

Demo

View Demo

Sourcecode

on github

Note

This is an experiment. It's hacky and you should not use it as an example of good style - it's not.

For an upcoming canvas project I want to give the users the ability to upload the content of the canvas to an image sharing service. When looking for a suitable API I came across imgur.com the registration was trivial, and they support CORS and base64/dataurl uploads, perfect!

// trigger me onclick
function share(){
    try {
        var img = canvas.toDataURL('image/jpeg', 0.9).split(',')[1];
    } catch(e) {
        var img = canvas.toDataURL().split(',')[1];
    }
    // open the popup in the click handler so it will not be blocked
    var w = window.open();
    w.document.write('Uploading...');
    // upload to imgur using jquery/CORS
    // https://developer.mozilla.org/En/HTTP_access_control
    $.ajax({
        url: 'http://api.imgur.com/2/upload.json',
        type: 'POST',
        data: {
            type: 'base64',
            // get your key here, quick and fast http://imgur.com/register/api_anon
            key: 'YOUR-API-KEY',
            name: 'neon.jpg',
            title: 'test title',
            caption: 'test caption',
            image: img
        },
        dataType: 'json'
    }).success(function(data) {
        w.location.href = data['upload']['links']['imgur_page'];
    }).error(function() {
        alert('Could not reach api.imgur.com. Sorry :(');
        w.close();
    });
}

I finally finished my first WebGL demo. Try it and let me know how you like it.

Sourcecode

You can find the source code on github if you want to get into some hacking.

Compatibility

To run the demo you'll need a browser that supports webgl and the OES_TEXTURE_FLOAT extension. At the moment this means Google Chrome 12 or Firefox Aurora (6.0a2). The extension is needed for HDR rendering.

I finally found a way to optimize 2d canvas drawing on the iPhone 4. Because of the retina display the canvas seems to be rescaled in a slow way (in software?). So even though the rendering itself is relatively fast, the end result is slow.

Setting the Viewport

The first step is to set the viewport scale to 0.5 which will result in having one pixel per css pixel.

<meta name="viewport" content="width=device-width, initial-scale=0.5, user-scalable=no"/>

So now the rendering is fast, but the picture is tiny.

3D transforms to the rescue

To scale the picture up we can use css 3d transforms which are fast.

canvas { -webkit-transform: scale3d(2, 2, 0) translate3d(200px, 110px, 0); }

Also note the translation to move the image back into place as it is being scaled from the origin.

That's it you got yourself a massive performance boost in about two lines of code. :)

I'm doing my first steps into webgl land. It's definitely a love hate relationship, and I still have a lot to learn and improve. :)

I might post the actual demo at a later stage, right now it's a complete mess.

Play it now

Space Break

Space Break is a html5 acrade 'ball and paddle' game written in coffee-script. It features levels full of explosives, extra balls and even nukes. I hope you will enjoy it.

History

Space Break started out as coffee-break - a little project I did to get into coffee script. Because it turned out to be a lot of fun I decided to turn it into a complete game.

Technology

Space Break uses the canvas tag for rendering. The sound effects were created using csound and played using the audio tag. The graphics were made using the gimp and blender. Rake is used for controlling the asset pipeline. All the assets of the game (music, sounds, graphics) are self made - programmer art.

Browsers

Firefox 4 (3.6 kind of works), Chrome 9 and Safari (no ogg - no audio) work. Opera is crashy. Mobile safari on the iPad also works but the frame rate is low. Could be fixed with a bit of optimization.

Source and License

The code and assets are of course on github.

The Sourcecode (break.coffee, Rakefile) is licensed under the GPL V3.

The assets are licensed as Creative Commons BY NC SA

PLEASE LET ME KNOW IF YOU DO SOMETHING COOL WITH IT.

If the licensing doesn't work for you, please let me know.

Feedback

Feedback, both positive and negative is of course appreciated. Just leave me a comment, tweet or send me a email.