C#可以使用Drawing處理圖片，但儲存時預設壓縮品質較差，使用下面方法可以自訂壓縮比率。

System.Drawing.Image image = System.Drawing.Image.FromFile(@"C:\a.png");
EncoderParameters myEncoderParameters = new EncoderParameters(1);
myEncoderParameters.Param[0] = new EncoderParameter(Encoder.Quality, Convert.ToInt64(60)); //品質60
image.Save(@"C:\b.png", GetEncoder(ImageFormat.Png), myEncoderParameters); //儲存成png
image.Dispose();

private ImageCodecInfo GetEncoder(ImageFormat format)
{
	ImageCodecInfo[] codecs = ImageCodecInfo.GetImageDecoders();
	foreach (ImageCodecInfo codec in codecs)
	{
		if (codec.FormatID == format.Guid) return codec;
	}
	return null;
}