[javascript] Compress images on client side before uploading

Does anyone know of any free script that compresses JPG, GIF and PNG files as much as possible?

I'm late to the party, but this solution worked for me quite well. Based on this library, you can use a function lik this - setting the image, quality, max-width, and output format (jepg,png):

function compress(source_img_obj, quality, maxWidth, output_format){
    var mime_type = "image/jpeg";
    if(typeof output_format !== "undefined" && output_format=="png"){
        mime_type = "image/png";
    }

    maxWidth = maxWidth || 1000;
    var natW = source_img_obj.naturalWidth;
    var natH = source_img_obj.naturalHeight;
    var ratio = natH / natW;
    if (natW > maxWidth) {
        natW = maxWidth;
        natH = ratio * maxWidth;
    }

    var cvs = document.createElement('canvas');
    cvs.width = natW;
    cvs.height = natH;

    var ctx = cvs.getContext("2d").drawImage(source_img_obj, 0, 0, natW, natH);
    var newImageData = cvs.toDataURL(mime_type, quality/100);
    var result_image_obj = new Image();
    result_image_obj.src = newImageData;
    return result_image_obj;
}

I read about an experiment here: http://webreflection.blogspot.com/2010/12/100-client-side-image-resizing.html

The theory is that you can use canvas to resize the images on the client before uploading. The prototype example seems to work only in recent browsers, interesting idea though...

However, I’m not sure about using canvas to compress images, but you can certainly resize them.

If you are looking for a library to carry out client-side image compression, you can check this out:compress.js. This will basically help you compress multiple images purely with JavaScript and convert them to base64 string. You can optionally set the maximum size in MB and also the preferred image quality.

I just developed a javascript library called JIC to solve that problem. It allows you to compress jpg and png on the client side 100% with javascript and no external libraries required!

You can try the demo here : http://makeitsolutions.com/labs/jic and get the sources here : https://github.com/brunobar79/J-I-C