修改jpg的图片大小

using System.Drawing.Imaging;

public void ResizePic(string oldFilePath, int thumbnailImageWidth, int thumbnailImageHeight, string targetFilePath)
{
using (Image oldImg = Image.FromFile(oldFilePath))
{
using (Image thumnailImg = oldImg.GetThumbnailImage(thumbnailImageWidth, thumbnailImageHeight, null, IntPtr.Zero))
{
ImageCodecInfo imgCodeInfo = GetImageCodeInfo("image/jpeg");
if (imgCodeInfo != null)
{
EncoderParameters encodeParameters = new EncoderParameters(1);
encodeParameters.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, (long)100);
Bitmap bmp = new Bitmap(thumnailImg);
encodeParameters.Dispose();
encodeParameters = null;
bmp.Save(targetFilePath, imgCodeInfo, encodeParameters);
bmp.Dispose();
}
}
}
}

private static ImageCodecInfo GetImageCodeInfo(string mimeType)
{
ImageCodecInfo[] encoders;
encoders = ImageCodecInfo.GetImageEncoders();
for (int i = 0; i < encoders.Length; i++)
{
if (encoders[i].MimeType == mimeType)
return encoders[i];
}
return null;
}