OutOfMemoryException when decoding and encoding JPEG images in a loop

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C#

hello,

first a little background.
I digitize my old Super8 movies using a flatbed scanner
(for details see http://hosting.aktionspotenzial.de/CineToVidWiki )

I recognized, that I get better results, if I scan the movie strips
upside down (emulsion towards the scanner glass). To do this I must also scan the strips from film end towards film start (backward).
To extract the frames properly (that is: not to get mirrored images and a backwards running film) I have to renumber the files containing the strips and I also have to horizontally flip the images.

Therefore I have written a little program, that can do that for me.
The conversion and image saving method is shown below. This method is called in a loop (from a Forms class providing the GUI for the application), this loop provides the filenames of the image source and the image target.
BUT:
As the images are pretty large ( 4MB in JPEG compression, about 170 MB as a Windows Bitmap) this works only for a few images (but this exactly as intended), and then stops with an OutOfMemory Exception.

The loop code looks like this

for (i = startFileIndex; i <= endFileIndex; i++)
{  /* 001 start for */
    errFileName = fileEntries[i];
    aFileURLB = stripDirectoryB + fileEntries[i];
    aFileURLF = stripDirectoryF + fileEntries[numberOfStrips - i - 1];
    aNewImage = new NewImage();
    imgIndex  = aNewImage.flipAndRenameImage(aFileURLB, aFileURLF, errFileName,i);
    ........
    ......
    aNewImage = null;
}  /* 001 end for */

As you can see in the provided code below, I have tried several things to free memory in the heap, but without any success.


Has anybody an idea, what to do, to get rid of the OutOfMemory exception. I would appreciate that very much.



---------- this is the code that is called from the loop -----------
---------- in each cycle of the calling loop a new instance of NewImage is created and discarded ( set to NULL ) at the end of the cycle -------------------------------

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Drawing.Imaging;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO;
using System.Windows.Media.Imaging;
// using System.Windows.Controls;

namespace ReformatStrips
{
    public class NewImage
    {

        public Stream imageStreamSource;
        public FileStream imageStreamTarget;
        public BitmapSource bitmapSource;
        public JpegBitmapDecoder decoder;
        public JpegBitmapEncoder encoder;

        public NewImage()
        {
            // Nothings specific to do
        }

        public int flipAndRenameImage(string aFileURLB, string aFileURLF, string errFileName, int fileIndex)
        {  /*  start of method */
            try
            {
                // Open a Stream and decode a JPEG image
                imageStreamSource = new FileStream(aFileURLB, FileMode.Open, FileAccess.Read, FileShare.Read);
                decoder = new JpegBitmapDecoder(imageStreamSource, BitmapCreateOptions.PreservePixelFormat, BitmapCacheOption.Default);
                bitmapSource = decoder.Frames[0];

                imageStreamTarget = new FileStream(aFileURLF, FileMode.Create, FileAccess.Write, FileShare.ReadWrite);
                encoder = new JpegBitmapEncoder();
                encoder.FlipHorizontal = true;
                encoder.Frames.Add(BitmapFrame.Create(bitmapSource));
                encoder.Save(imageStreamTarget);
                imageStreamTarget.Flush();

                imageStreamSource.Close();
                imageStreamTarget.Close();
                imageStreamSource.Dispose();
                imageStreamTarget.Dispose();
                bitmapSource = null;
                imageStreamSource = null;
                imageStreamTarget = null;
                decoder = null;
                encoder = null;
                fileIndex = 0;
 
                GC.WaitForFullGCComplete(1000);
                GC.Collect(0, GCCollectionMode.Forced);
            }
            catch (Exception e)
            {
                imageStreamTarget.Flush();
                imageStreamTarget.Close();
                GC.WaitForFullGCComplete(1000);
                GC.Collect(0, GCCollectionMode.Forced);

                Console.WriteLine(e.ToString());
            }
            return fileIndex;
        }  /*  end of method */
    }
}