C#图像透明度调整的方法

//定义图像透明度调整函数public Bitmap PTransparentAdjust(Bitmap src,int num){  try  {   int w = src.Width;   int h = src.Height;   Bitmap dstBitmap = new Bitmap(src.Width, src.Height, System.Drawing.Imaging.PixelFormat.Format32bppArgb);   System.Drawing.Imaging.BitmapData srcData = src.LockBits(new Rectangle(0, 0, w, h), System.Drawing.Imaging.ImageLockMode.ReadOnly, System.Drawing.Imaging.PixelFormat.Format32bppArgb);   System.Drawing.Imaging.BitmapData dstData = dstBitmap.LockBits(new Rectangle(0, 0, w, h), System.Drawing.Imaging.ImageLockMode.WriteOnly, System.Drawing.Imaging.PixelFormat.Format32bppArgb);   unsafe   {     byte* pIn = (byte*)srcData.Scan0.ToPointer();     byte* pOut = (byte*)dstData.Scan0.ToPointer();     byte* p;     int stride = srcData.Stride;     int r, g, b;     for (int y = 0; y < h; y++)     {     for (int x = 0; x < w; x++)     {       p = pIn;       b = pIn[0];       g = pIn[1];       r = pIn[2];       pOut[1] = (byte)g;       pOut[2] = (byte)r;       pOut[3] = (byte)num;       pOut[0] = (byte)b;       pIn += 4;       pOut += 4;     }     pIn += srcData.Stride - w * 4;     pOut += srcData.Stride - w * 4;     }     src.UnlockBits(srcData);     dstBitmap.UnlockBits(dstData);     return dstBitmap;   }  }  catch (Exception e)  {   MessageBox.Show(e.Message.ToString());   return null;  }}