for (int y = 0; y < height; y++)
{
 for (int x = 0; x < width; x++)
 {
  Color c = bmp.GetPixel(x, y);
  int R = c.R; int G = c.G; int B = c.B;
  byte temp = (byte)(B * 0.114 + G * 0.587 + R * 0.299);
  if (temp >= 0 && temp <= 63)
  {
   bmp.SetPixel(x, y, Color.FromArgb(0, (byte)(4 * temp), (byte)255));
  }
  if (temp >= 64 && temp <= 127)
  {
   bmp.SetPixel(x, y, Color.FromArgb(0, 255, (byte)(510 - 4 * temp)));
 
  }
  if (temp >= 128 && temp <= 191)
  {
   bmp.SetPixel(x, y, Color.FromArgb((byte)(4 * temp - 510), 255, 0));
  }
  if (temp >= 192 && temp <= 255)
  {
   bmp.SetPixel(x,y, Color.FromArgb(255, (byte)(1022 - 4 * temp),0));
  }
 }
}

for (int y = 50; y < 100; y++)
 {
  for (int x = 50; x < 100; x++)
  {
   // 处理指定位置像素的亮度

   Color c = b.GetPixel(x, y);

   int R = c.R; int G = c.G; int B = c.B;

   R = R + degree; if (R > 255) R = 255;

   G = G + degree; if (G > 255) G = 255;

   B = B + degree; if (B > 255) B = 255;

   b.SetPixel(x, y, Color.FromArgb(R, G, B));

  }

 }//其中degree是亮度阶梯度