使用itextsharpes压缩pdf图像会导致内存不足

我把代码放在这个线程中: PDF Compression with iTextSharp

im有一个异常“内存不足”,pdf im处理有47个图像,每个图像的权重不同,使pdf为16.5mb。

代码相同:

public void ReduceResolution(PdfReader reader, long quality)
{
    int n = reader.XrefSize;
    for (int i = 0; i < n; i++)
    {
        PdfObject obj = reader.GetPdfObject(i);
        if (obj == null || !obj.IsStream()) { continue; }

        PdfDictionary dict = (PdfDictionary)PdfReader.GetPdfObject(obj);
        PdfName subType = (PdfName)PdfReader.GetPdfObject(
          dict.Get(PdfName.SUBTYPE)
        );
        if (!PdfName.IMAGE.Equals(subType)) { continue; }

        PRStream stream = (PRStream)obj;
        try
        {
            PdfImageObject image = new PdfImageObject(stream);
            PdfName filter = (PdfName)image.Get(PdfName.FILTER);
            if (
              PdfName.JBIG2DECODE.Equals(filter)
              || PdfName.JPXDECODE.Equals(filter)
              || PdfName.CCITTFAXDECODE.Equals(filter)
              || PdfName.FLATEDECODE.Equals(filter)
            ) continue;

            System.Drawing.Image img = image.GetDrawingImage();
            if (img == null) continue;

            var ll = ImageToByteArray(img);
            int width = img.Width;
            int height = img.Height;
            using (System.Drawing.Bitmap dotnetImg =
               new System.Drawing.Bitmap(img))
            {
                // set codec to jpeg type => jpeg index codec is "1"
                System.Drawing.Imaging.ImageCodecInfo codec =
                System.Drawing.Imaging.ImageCodecInfo.GetImageEncoders()[1];
                // set parameters for image quality
                System.Drawing.Imaging.EncoderParameters eParams =
                 new System.Drawing.Imaging.EncoderParameters(1);
                eParams.Param[0] =
                 new System.Drawing.Imaging.EncoderParameter(
                   System.Drawing.Imaging.Encoder.Quality, quality
                );
                using (MemoryStream msImg = new MemoryStream())
                {
                    dotnetImg.Save(msImg, codec, eParams);
                    msImg.Position = 0;
                    stream.SetData(msImg.ToArray());
                    stream.SetData(
                     msImg.ToArray(), false, PRStream.BEST_COMPRESSION
                    );
                    stream.Put(PdfName.TYPE, PdfName.XOBJECT);
                    stream.Put(PdfName.SUBTYPE, PdfName.IMAGE);
                    stream.Put(PdfName.FILTER, filter);
                    stream.Put(PdfName.FILTER, PdfName.DCTDECODE);
                    stream.Put(PdfName.WIDTH, new PdfNumber(width));
                    stream.Put(PdfName.HEIGHT, new PdfNumber(height));
                    stream.Put(PdfName.BITSPERCOMPONENT, new PdfNumber(8));
                    stream.Put(PdfName.COLORSPACE, PdfName.DEVICERGB);
                }
            }
        }
        catch(Exception ex)
        {
            // throw ex;
            // iText[Sharp] can't handle all image types...
        }
        finally
        {
            // may or may not help      
            reader.RemoveUnusedObjects();
        }
    }
}

它发生在第一个映像之后,第二个映像似乎是x个足够大的字节,导致异常。

有什么方法可以避免这种类型的错误,是什么导致的?