//反色
public static bool Invert(Bitmap b)
{
// GDI+ still lies to us - the return format is BGR, NOT RGB.
BitmapData bmData = b.LockBits(new Rectangle(0, 0, b.Width, b.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
int stride = bmData.Stride;
System.IntPtr Scan0 = bmData.Scan0;
unsafe
{
byte * p = (byte *)(void *)Scan0;
int nOffset = stride - b.Width*3;
int nWidth = b.Width * 3;