MSDN：C#（.NET）自带的图像压缩代码

private void VaryQualityLevel(){    // Get a bitmap.    Bitmap bmp1 = new Bitmap(@"c:/TestPhoto.jpg");    ImageCodecInfo jgpEncoder = GetEncoder(ImageFormat.Jpeg);    // Create an Encoder object based on the GUID    // for the Quality parameter category.    System.Drawing.Imaging.Encoder myEncoder =        System.Drawing.Imaging.Encoder.Quality;    // Create an EncoderParameters object.    // An EncoderParameters object has an array of EncoderParameter    // objects. In this case, there is only one    // EncoderParameter object in the array.    EncoderParameters myEncoderParameters = new EncoderParameters(1);    EncoderParameter myEncoderParameter = new EncoderParameter(myEncoder, 50L);    myEncoderParameters.Param[0] = myEncoderParameter;    bmp1.Save(@"c:/TestPhotoQualityFifty.jpg", jgpEncoder, myEncoderParameters);    myEncoderParameter = new EncoderParameter(myEncoder, 100L);    myEncoderParameters.Param[0] = myEncoderParameter;    bmp1.Save(@"c:/TestPhotoQualityHundred.jpg", jgpEncoder, myEncoderParameters);    // Save the bitmap as a JPG file with zero quality level compression.    myEncoderParameter = new EncoderParameter(myEncoder, 0L);    myEncoderParameters.Param[0] = myEncoderParameter;    bmp1.Save(@"c:/TestPhotoQualityZero.jpg", jgpEncoder, myEncoderParameters);}...private ImageCodecInfo GetEncoder(ImageFormat format){    ImageCodecInfo[] codecs = ImageCodecInfo.GetImageDecoders();    foreach (ImageCodecInfo codec in codecs)    {        if (codec.FormatID == format.Guid)        {            return codec;        }    }    return null;}

效果还是可以的，有兴趣的可以试试。