function processCanvasRGBA(canvas, topX, topY, width, height, radius) {
  if (isNaN(radius) || radius < 1) {
    return;
  }

  radius |= 0;
  var imageData = getImageDataFromCanvas(canvas, topX, topY, width, height);
  imageData = processImageDataRGBA(imageData, topX, topY, width, height, radius);
  canvas.getContext('2d').putImageData(imageData, topX, topY);
}
@param {ImageData} imageData
@param {Integer} topX
@param {Integer} topY
@param {Integer} width
@param {Integer} height
@param {Float} radius
@returns {ImageData}