gistfile1.txt

 canvas.forEach(imageData, function(r, g, b, a, w, i, j) {
                pixel = ~~(r*0.299 + b*0.587 + g*0.114);

                if (i === 0 & j === 0) {
                    pixelSum = pixel;
                    pixelSumSquare = pixel*pixel;
                }
                else if (i === 0) {
                    pixelSum = pixel + integralImage[i*width + (j - 1)];
                    pixelSumSquare = pixel*pixel + integralImageSquare[i*width + (j - 1)];
                }
                else if (j === 0) {
                    pixelSum = pixel + integralImage[(i - 1)*width + j];
                    pixelSumSquare = pixel*pixel + integralImageSquare[(i - 1)*width + j];
                }
                else {
                    pixelSum = pixel + integralImage[i*width + (j - 1)] + integralImage[(i - 1)*width + j] - integralImage[(i - 1)*width + (j - 1)];
                    pixelSumSquare = pixel*pixel + integralImageSquare[i*width + (j - 1)] + integralImageSquare[(i - 1)*width + j] - integralImageSquare[(i - 1)*width + (j - 1)];
                }

                // pixelSumSquare += pixel*pixel;

                integralImage[imageLen] = pixelSum;
                integralImageSquare[imageLen] = pixelSumSquare;
                imageLen++;
            });