How to handle png pictures

[chongbo2013]

I need to deal with the picture with transparency SketchFilter.cpp how should I modify

[chongbo2013]

afterGray = abs(xVal) + abs(yVal);
        afterGray = min(255, max(0, afterGray));
        int pixel_index = i * width + j;
        if (pixel_index < width * height) {
            if (afterGray > threshold) {
                pixels[i * width + j] = RGB2Color(neonR, neonG, neonB);
            } else
                pixels[i * width + j] = ARGB2Color(0,1, 1, 1);
        }

[chongbo2013]

thank u source i I have modified it successfully