Why does Image.FromFile keep a file handle open sometimes?

Question

I am doing a lot of image processing in GDI+ in .NET in an ASP.NET application.

I frequently find that Image.FromFile() is keeping a file handle open.

Why is this? What is the best way to open an image without the file handle being retained.

• NB: I'm not doing anything stupid like keeping the Image object lying around - and even if I was I woudlnt expect the file handle to be kept active

Answer 1

I went through the same journey as a few other posters on this thread. Things I noted:

1. Using Image.FromFile does seem unpredictable on when it releases the file handle. Calling the Image.Dispose() did not release the file handle in all cases.

2. Using a FileStream and the Image.FromStream method works, and releases the handle on the file if you call Dispose() on the FileStream or wrap the whole thing in a Using {} statement as recommended by Kris. However if you then attempt to save the Image object to a stream, the Image.Save method throws an exception "A generic error occured in GDI+". Presumably something in the Save method wants to know about the originating file.

3. Steven's approach worked for me. I was able to delete the originating file with the Image object in memory. I was also able to save the Image to both a stream and a file (I needed to do both of these things). I was also able to save to a file with the same name as the originating file, something that is documented as not possible if you use the Image.FromFile method (I find this weird since surely this is the most likely use case, but hey.)

So to summarise, open your Image like this:

Image img = Image.FromStream(new MemoryStream(File.ReadAllBytes(path)));

You are then free to manipulate it (and the originating file) as you see fit.

Answer 2

I have had the same problem and resorted to reading the file using

return Image.FromStream(new MemoryStream(File.ReadAllBytes(fileName)));

Answer 3

Image.FromFile keeps the file handle open until the image is disposed. From the MSDN:

"The file remains locked until the Image is disposed."

Use Image.FromStream, and you won't have the problem.

using(var fs = new FileStream(filename, FileMode.Open, FileAccess.Read))
{
    return Image.FromStream(fs);
}

Edit: (a year and a bit later)

The above code is dangerous as it is unpredictable, at some point in time (after closing the filestream) you may get the dreaded "A generic error occurred in GDI+". I would amend it to:

Image tmpImage;
Bitmap returnImage;

using(var fs = new FileStream(filename, FileMode.Open, FileAccess.Read))
{
    tmpImage = Image.FromStream(fs);
    returnImage = new Bitmap(tmpImage);
    tmpImage.Dispose();
}

return returnImage;

Answer 4

Make sure you are Disposing properly.

using (Image.FromFile("path")) {}

The using expression is shorthand for

IDisposable obj;
try { }
finally 
{
    obj.Dispose();
}

@Rex in the case of Image.Dispose it calls GdipDisposeImage extern / native Win32 call in it's Dispose().

IDisposable is used as a mechanism to free unmanaged resources (Which file handles are)

Answer 5

I also tried all your tips (ReadAllBytes, FileStream=>FromStream=>newBitmap() to make a copy, etc.) and they all worked. However, I wondered, if you could find something shorter, and

using (Image temp = Image.FromFile(path))
{
    return new Bitmap(temp);
}

appears to work, too, as it disposes the file handle as well as the original Image-object and creates a new Bitmap-object, that is independent from the original file and therefore can be saved to a stream or file without errors.

Answer 6

I would have to point my finger at the Garbage Collector. Leaving it around is not really the issue if you are at the mercy of Garbage Collection.

This guy had a similar complaint... and he found a workaround of using a FileStream object rather than loading directly from the file.

public static Image LoadImageFromFile(string fileName)
{
    Image theImage = null;

    fileStream = new FileStream(fileName, FileMode.Open, FileAccess.Read);
    {
        byte[] img;
        img = new byte[fileStream.Length];
        fileStream.Read(img, 0, img.Length);
        fileStream.Close();
        theImage = Image.FromStream(new MemoryStream(img));
        img = null;
    }

...

It seems like a complete hack...

Answer 7

As mentioned above the Microsoft work around causes a GDI+ error after several images have been loaded. The VB solution for me as mentioned above by Steven is

picTemp.Image = Image.FromStream(New System.IO.MemoryStream(My.Computer.FileSystem.ReadAllBytes(strFl)))

Answer 8

I just encountered the same problem, where I was trying to merge multiple, single-page TIFF files into one multipart TIFF image. I needed to use Image.Save() and 'Image.SaveAdd()`: https://msdn.microsoft.com/en-us/library/windows/desktop/ms533839%28v=vs.85%29.aspx

The solution in my case was to call ".Dispose()" for each of the images, as soon as I was done with them:

' Iterate through each single-page source .tiff file
Dim initialTiff As System.Drawing.Image = Nothing
For Each filePath As String In srcFilePaths

    Using fs As System.IO.FileStream = File.Open(filePath, FileMode.Open, FileAccess.Read)
        If initialTiff Is Nothing Then
            ' ... Save 1st page of multi-part .TIFF
            initialTiff = Image.FromStream(fs)
            encoderParams.Param(0) = New EncoderParameter(Encoder.Compression, EncoderValue.CompressionCCITT4)
            encoderParams.Param(1) = New EncoderParameter(Encoder.SaveFlag, EncoderValue.MultiFrame)
            initialTiff.Save(outputFilePath, encoderInfo, encoderParams)
        Else
            ' ... Save subsequent pages
            Dim newTiff As System.Drawing.Image = Image.FromStream(fs)
            encoderParams = New EncoderParameters(2)
            encoderParams.Param(0) = New EncoderParameter(Encoder.Compression, EncoderValue.CompressionCCITT4)
            encoderParams.Param(1) = New EncoderParameter(Encoder.SaveFlag, EncoderValue.FrameDimensionPage)
            initialTiff.SaveAdd(newTiff, encoderParams)
            newTiff.Dispose()
        End If
    End Using

Next

' Make sure to close the file
initialTiff.Dispose()