code: function (inData, outData, width, height, options) {
          options = defaultOptions(options, {amount: 1, angle: 0});
          var i, n = width * height * 4,
              amount = options.amount,
              angle = options.angle,
              x = Math.cos(-angle) * amount,
              y = Math.sin(-angle) * amount,
  
              a00 = -x - y,
              a10 = -x,
              a20 = y - x,
              a01 = -y,
              a21 = y,
              a02 = -y + x,
              a12 = x,
              a22 = y + x,
  
              tmpData = [];
  
          convolve3x3(inData, tmpData, width, height,
              [
                  [a00, a01, a02],
                  [a10, 0, a12],
                  [a20, a21, a22]
              ]);
  
          for (i = 0; i < n; i += 4) {
              outData[i] = 128 + tmpData[i];
              outData[i + 1] = 128 + tmpData[i + 1];
              outData[i + 2] = 128 + tmpData[i + 2];
              outData[i + 3] = inData[i + 3];
          }
      }
docs: 3x3 directional emboss