Question

I have many slideshows showing a project each. I would like to make all non-selected slideshows grey (not just fade their opacity or put a milky overlay over them, which I can do) to make the currently selected one visually stand out. It should work on current webkit browsers and from IE8 upwards. I tried to work with the canvas to grey them out, but it breaks the slideshows and other things on my site. Is there another way to grey out images/slideshows via CSS & jQuery?

If only this -webkit-filter: grayscale(100%); would work in Safari, Chrome, Firefox and IE>=8…

<script type="text/javascript">
$(window).load(function(){

    $('.item img').each(function(){
        var el = $(this);
        el.css({"position":"absolute"}).wrap("<div class='img_wrapper' style='display: inline-block'>").clone().addClass('img_grayscale').css({"position":"absolute","z-index":"998","opacity":"0"}).insertBefore(el).queue(function(){
            var el = $(this);
            el.parent().css({"width":this.width,"height":this.height});
            el.dequeue();
        });
        this.src = grayscale(this.src);
    });

    $('.item img').mouseover(function(){
        $(this).parent().find('img:first').stop().animate({opacity:1}, 1000);
    })
    $('.img_grayscale').mouseout(function(){
        $(this).stop().animate({opacity:0}, 1000);
    });     
});

function grayscale(src){
    var canvas = document.createElement('canvas');
    var ctx = canvas.getContext('2d');
    var imgObj = new Image();
    imgObj.src = src;
    canvas.width = imgObj.width;
    canvas.height = imgObj.height; 
    ctx.drawImage(imgObj, 0, 0); 
    var imgPixels = ctx.getImageData(0, 0, canvas.width, canvas.height);
    for(var y = 0; y < imgPixels.height; y++){
        for(var x = 0; x < imgPixels.width; x++){
            var i = (y * 4) * imgPixels.width + x * 4;
            var avg = (imgPixels.data[i] + imgPixels.data[i + 1] + imgPixels.data[i + 2]) / 3;
            imgPixels.data[i] = avg; 
            imgPixels.data[i + 1] = avg; 
            imgPixels.data[i + 2] = avg;
        }
    }
ctx.putImageData(imgPixels, 0, 0, 0, 0, imgPixels.width, imgPixels.height);
return canvas.toDataURL();
}    
</script>

Answer 1

As far as i know CSS filters are only implemented in webkit browsers, so if you need compatibility between browsers you have to stick with canvas. Here is a tiny library which do the job:

http://cdn.ultranoir.com/js/lib/imagetogreyscale/ImageToGreyscale.js

and the original one:

http://www.ajaxblender.com/howto-convert-image-to-grayscale-using-javascript.html