processing_计算图像的梯度和切向，并用箭头和流线表示(附下载链接)

    void bgrTogray(){
    for(int i=0;i<p1.width;i++){
        for(int j=0;j<p1.height;j++){
          int xy = i + p1.width * j;
          float r = red(p1.pixels[xy]);
          float g = green(p1.pixels[xy]);
          float b = blue(p1.pixels[xy]);
          int mix = int(r * 0.299f + g * 0.587f + b * 0.114f);
          if(mix>255)mix = 255;
          color c1 = color(mix,mix,mix);
          p1.pixels[xy] = c1;
        }
    }
    }