C#中生成透明Gif文件
在C#中使用Graphics.Clear(Color.Transparent)生成gif格式透明文件時(shí),設(shè)置透明不起作用。使用Bitmap.MakeTransparent 方法同樣也不能使gif文件透明。這兩個(gè)問題也是微軟的設(shè)計(jì)使然,和gif文件格式有關(guān)系。
如果要在c#中編程實(shí)現(xiàn)透明色,必須另寫代碼,下面是一位老外的代碼
-->///
/// Make the image transparent.
/// The input is the color which you want to make transparent.
///
///The color to make transparent.
///The bitmap to make transparent.
///New memory stream containing transparent background gif.
public Bitmap MakeTransparentGif(Bitmap bitmap, Color color)
{
byte R = color.R;
byte G = color.G;
byte B = color.B;
MemoryStream fin = new MemoryStream();
bitmap.Save(fin, System.Drawing.Imaging.ImageFormat.Gif);
MemoryStream fout = new MemoryStream((int)fin.Length);
int count = 0;
byte[] buf = new byte[256];
byte transparentIdx = 0;
fin.Seek(0, SeekOrigin.Begin);
//header
count = fin.Read(buf, 0, 13);
if ((buf[0] != 71) || (buf[1] != 73) || (buf[2] != 70)) return null; //GIF
fout.Write(buf, 0, 13);
int i = 0;
if ((buf[10] & 0x80) > 0)
{
i = 1 << ((buf[10] & 7) + 1) == 256 ? 256 : 0;
}
for (; i != 0; i--)
{
fin.Read(buf, 0, 3);
if ((buf[0] == R) && (buf[1] == G) && (buf[2] == B))
{
transparentIdx = (byte)(256 - i);
}
fout.Write(buf, 0, 3);
}
bool gcePresent = false;
while (true)
{
fin.Read(buf, 0, 1);
fout.Write(buf, 0, 1);
if (buf[0] != 0x21) break;
fin.Read(buf, 0, 1);
fout.Write(buf, 0, 1);
gcePresent = (buf[0] == 0xf9);
while (true)
{
fin.Read(buf, 0, 1);
fout.Write(buf, 0, 1);
if (buf[0] == 0) break;
count = buf[0];
if (fin.Read(buf, 0, count) != count) return null;
if (gcePresent)
{
if (count == 4)
{
buf[0] |= 0x01;
buf[3] = transparentIdx;
}
}
fout.Write(buf, 0, count);
}
}
while (count > 0)
{
count = fin.Read(buf, 0, 1);
fout.Write(buf, 0, 1);
}
fin.Close();
fout.Flush();
return new Bitmap(fout);
}
在生成圖片之后調(diào)用此方法,即可使gif顯示透明色。
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