Source: https://github.com/viliusle/Hermite-resize/blob/master/hermite.js
http://jsfiddle.net/9g9Nv/96/

var canvas = document.getElementById("cc");
var ctx = canvas.getContext("2d");

var img = new Image();
img.crossOrigin = "Anonymous"; //cors support
img.onload = function(){
    var W = img.width;
    var H = img.height;
    canvas.width = W;
    canvas.height = H;
    ctx.drawImage(img, 0, 0); //draw image
    
    //resize by ratio
    //var ratio = 0.43895525; //from 0 to 1
    //resample_hermite(canvas, W, H, Math.round(W*ratio), Math.round(H*ratio));
    
    //resize manually
    resample_hermite(canvas, W, H, 439, 222);
}
img.src = 'http://i.imgur.com/8VsK7gS.png';




function resample_hermite(canvas, W, H, W2, H2){
	var time1 = Date.now();
	W2 = Math.round(W2);
	H2 = Math.round(H2);
	var img = canvas.getContext("2d").getImageData(0, 0, W, H);
	var img2 = canvas.getContext("2d").getImageData(0, 0, W2, H2);
	var data = img.data;
	var data2 = img2.data;
	var ratio_w = W / W2;
	var ratio_h = H / H2;
	var ratio_w_half = Math.ceil(ratio_w/2);
	var ratio_h_half = Math.ceil(ratio_h/2);
	
	for(var j = 0; j < H2; j++){
		for(var i = 0; i < W2; i++){
			var x2 = (i + j*W2) * 4;
			var weight = 0;
			var weights = 0;
			var weights_alpha = 0;
			var gx_r = gx_g = gx_b = gx_a = 0;
			var center_y = (j + 0.5) * ratio_h;
			for(var yy = Math.floor(j * ratio_h); yy < (j + 1) * ratio_h; yy++){
				var dy = Math.abs(center_y - (yy + 0.5)) / ratio_h_half;
				var center_x = (i + 0.5) * ratio_w;
				var w0 = dy*dy //pre-calc part of w
				for(var xx = Math.floor(i * ratio_w); xx < (i + 1) * ratio_w; xx++){
					var dx = Math.abs(center_x - (xx + 0.5)) / ratio_w_half;
					var w = Math.sqrt(w0 + dx*dx);
					if(w >= -1 && w <= 1){
						//hermite filter
						weight = 2 * w*w*w - 3*w*w + 1;
						if(weight > 0){
							dx = 4*(xx + yy*W);
							//alpha
							gx_a += weight * data[dx + 3];
							weights_alpha += weight;
							//colors
							if(data[dx + 3] < 255)
								weight = weight * data[dx + 3] / 250;
							gx_r += weight * data[dx];
							gx_g += weight * data[dx + 1];
							gx_b += weight * data[dx + 2];
							weights += weight;
							}
						}
					}		
				}
			data2[x2]     = gx_r / weights;
			data2[x2 + 1] = gx_g / weights;
			data2[x2 + 2] = gx_b / weights;
			data2[x2 + 3] = gx_a / weights_alpha;
			}
		}
	console.log("hermite = "+(Math.round(Date.now() - time1)/1000)+" s");
	canvas.getContext("2d").clearRect(0, 0, Math.max(W, W2), Math.max(H, H2));
    canvas.width = W2;
    canvas.height = H2;
	canvas.getContext("2d").putImageData(img2, 0, 0);
}