C#设置图片透明度

逐个像素进行Alpha值的设置，网上其他的代码不能处理有透明背景的图片，因此要对Alpha、R、G、B均为0的透明色进行特殊处理，不做转换。

         private Bitmap SetImageOpacity(Image srcImage, int opacity)
         {
             Bitmap pic = new Bitmap(srcImage);
             for (int w = ; w < pic.Width; w++)
             {
                 for (int h = ; h < pic.Height; h++)
                 {
                     Color c = pic.GetPixel(w, h);
                     Color newC;
                     if (!c.Equals(Color.FromArgb(, , , )))
                     {
                         newC = Color.FromArgb(opacity, c);
                     }
                     else
                     {
                         newC = c;
                     }
                     pic.SetPixel(w, h, newC);
                 }
             }
             return pic;
         }

         private Image SetImageOpacity2(Image srcImage, int opacity)
         {
             Bitmap img = new Bitmap(srcImage);
             using (Bitmap bmp = new Bitmap(img.Width, img.Height, System.Drawing.Imaging.PixelFormat.Format32bppArgb))
             {
                 using (Graphics g = Graphics.FromImage(bmp))
                 {
                     g.DrawImage(img, , );
                     for (int h = ; h <= img.Height - ; h++)
                     {
                         for (int w = ; w <= img.Width - ; w++)
                         {
                             Color c = img.GetPixel(w, h);
                             if (!c.Equals(Color.FromArgb(, , , )))
                             {
                                 bmp.SetPixel(w, h, Color.FromArgb(opacity, c.R, c.G, c.B));
                             }
                             else
                             {
                                 bmp.SetPixel(w, h, Color.FromArgb(c.A, c.R, c.G, c.B));
                             }
                         }
                     }
                 }
                 return (Image)bmp.Clone();
             }
         }