试试这个，

IntPtr pval = IntPtr.Zero;
System.Drawing.Imaging.BitmapData bd = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
try
{
    pval=bd.Scan0;

    ...
}
finally
{
    bmp.UnlockBits(bd);
}