// http://asserttrue.blogspot.ca/2010/08/implementing-smart-blur-in-java.html
SmartBlurFilter = function () {
  var SENSITIVITY = 10
  var REGION_SIZE = 5
  var edge_zero_fill = true

	var kx = -((REGION_SIZE/2)|0), ky = -((REGION_SIZE/2)|0), klen = REGION_SIZE*REGION_SIZE

  var kernelArray = [
    1,1,1,1,1,1,1,1,1,
    1,1,1,1,1,1,1,1,1,
    1,1,1,1,1,1,1,1,1,
    1,1,1,1,1,1,1,1,1,
    1,1,1,1,1,1,1,1,1,
    1,1,1,1,1,1,1,1,1,
    1,1,1,1,1,1,1,1,1,
    1,1,1,1,1,1,1,1,1,
    1,1,1,1,1,1,1,1,1
  ]

  var kernel = new Kernel(9, 9, kernelArray)
  kernel.normalize()

  function lerp(a,b,amt) {
    return a + amt * (b - a);
  }

  function rmsError(src, i, size) {
    var ave = 0;

		var len = size*size, data = src.data

		var ix, iy
		var r,g,b,a
		var w = src.width, h = src.height
		ix = i%w
		iy = (i/w)|0
		it = i * 4
		r = g = b = a = 0
		for (var j = 0; j < klen; j++) {
			jx = ix +  j%size + kx
			jy = iy + ((j/size)|0) + ky
			jt = 4 * (jx + jy*w)
			if (0 > jx || jx > w || 0 > jy || jy > h) {
				if (edge_zero_fill) {
					continue
				}
				jt = it
			}
			r += data[jt]
// 			g += data[jt+1]
// 			b += data[jt+2]
// 			a += data[jt+3]
		}
    r /= klen
//     g /= klen
//     b /= klen
//     a /= klen

    var diff = 0
    var accumulator = 0

		for (var j = 0; j < klen; j++) {
			jx = ix +  j%size + kx
			jy = iy + ((j/size)|0) + ky
			jt = 4 * (jx + jy*w)
			if (0 > jx || jx > w || 0 > jy || jy > h) {
				if (edge_zero_fill) {
					continue
				}
				jt = it
			}
			diff = data[ jt ] - ave
			diff *= diff
			accumulator += diff
    }

    var rms = accumulator / klen
    rms = Math.sqrt(rms) / 255
    return rms
  }

  function lerpPixel( src, dest, blur, i, amt) {
  	dest[i]   = lerp(src[i],   blur[i],   amt)
  	dest[i+1] = lerp(src[i+1], blur[i+1], amt)
  	dest[i+2] = lerp(src[i+2], blur[i+2], amt)
  	dest[i+3] = lerp(src[i+3], blur[i+3], amt)
  }

  function blurImage( src, dest, blur, sensitivity ) {
    var newPixel = 0
    var amt = 0
    var size = REGION_SIZE
		var w = src.width, rms

		var srcData = src.data
		var destData = dest.data
		var blurData = blur.data
    for (var i = 0, len = srcData.length/4; i < len; i++) {

			rms = rmsError(src, i, size)

//			amt = rms < sensitivity ? rms/sensitivity : 1.0
			lerpPixel( srcData, destData, blurData, i*4, rms)
    }
    
    return dest
  }

  this.blur = function (src_canvas, dest_canvas) {
    var convolver = new ConvolveOp(kernel, ConvolveOp.EDGE_NO_OP, null);

    // clone image into target
    if (! dest_canvas) dest_canvas = document.createElement("canvas")
    var w = dest_canvas.width = src_canvas.width
    var h = dest_canvas.height = src_canvas.height
    var srcctx = src_canvas.getContext('2d')
    var destctx = dest_canvas.getContext('2d')

    destctx.drawImage(src_canvas, 0, 0);

    // get source pixels
    var src = srcctx.getImageData(0,0,w,h)
    var dest = destctx.getImageData(0,0,w,h)

    // blur the cloned image
    dest = convolver.filter(src, dest);

		destctx.putImageData(dest, 0,0)
    var blurred = destctx.getImageData(0,0,w,h)
    var dest = srcctx.getImageData(0,0,w,h)
    dest = blurImage(src, dest, blurred, SENSITIVITY)
		destctx.putImageData(dest, 0,0)

    return dest_canvas
  }
}