Image.RotateFlip leaking memory :/

Question

Although I have been programming for about 11 years(mostly VB6, last 6 months C#), it's THE first time to actually ask a question :) I have found all my answers from teh interwebz but this issue i can't solve myself. Your site is among the most helpful places i have got the best answers from!

I will show the code i'm using (an extract of what's relevant). Problem is that when using RotateFlip method then the memory is increasing rapidly to ~200M and then get's collected by GC after some time. The main method calling it iterates about 30 times per second so the performance is of utmost importance here. I have tried using graphics matrix transform but this sometimes fails and shows non-flipped image. The application itself is based on using a webcam, hiding the preview, taking the callback picture and showing it in picturebox. It then overlays a rectangle on if from another class. That's the reason to use callback and not preview window.

Capture.cs class:

internal Bitmap LiveImage;

    int ISampleGrabberCB.BufferCB(double bufferSize, IntPtr pBuffer, int bufferLen)
    {
        LiveImage = new Bitmap(_width, _height, _stride, PixelFormat.Format24bppRgb, pBuffer);

        if (ExpImg) // local bool, used rarely when the picture saving is triggered
        {
            LiveImage.RotateFlip(RotateFlipType.RotateNoneFlipY);
            var a = LiveImage.Clone(new Rectangle(Currect.Left, Currect.Top, Currect.Width, Currect.Height),
                                    LiveImage.PixelFormat);
            using (a)
                a.Save("ocr.bmp", ImageFormat.Bmp);

        }
        else // dmnit, rotateflip leaks like h*ll but matrix transform doesn't sometimes flip :S
        {
            LiveImage.RotateFlip(RotateFlipType.RotateNoneFlipY);
            /*using (var g = Graphics.FromImage(LiveImage))
            {
                g.Transform = _mtx;
                g.DrawImage(LiveImage, 0, 0);
            }*/
        }
        GC.Collect(); // gotta use it with rotateflip, otherwise it gets crazy big, like ~200M :O
        return 0;
    }
}

In main form i have an event that's updating the picture in the picturebox:

private void SetPic()
{
    pctCamera.Image = _cam.LiveImage;
    _cam.PicIsFree = false;
}

Because i need to get the image to main form which is in another class then i figured the most logical is the exposed Bitmap which is updated on every callback frame. The reason i don't want to use matrix transform is because it's slower and sometimes with this speed it fails to flip the image and the frequency of such behavior is quite different with different PC's with different hardware capabilities and CPU speeds, also the fastest framerate 30fps with a 1.2GHz CPU shows this very frequently.

So, can you help me to figure it out? I'm not actually using it in current version, i'm using the commented-out matrix transform because i feel bad for using GC.Collect :(

Thank You!!!

Answer 1

pctCamera.Image = _cam.LiveImage;

Heavy memory usage like you observe is a sure sign that you missed an opportunity to call Dispose() somewhere, letting the unmanaged resources (memory mostly) used by a bitmap get released early instead of letting the garbage collector do it. The quoted statement is one such case, you are not disposing the old image referenced by the picture box. Fix:

if (pctCamera.Image != null) pctCamera.Image.Dispose();
pctCamera.Image = _cam.LiveImage;

Answer 2

You can rewrite your code like this:

internal Bitmap LiveImage;

int ISampleGrabberCB.BufferCB(double bufferSize, IntPtr pBuffer, int bufferLen)
{
    using (LiveImage = new Bitmap(_width, _height, _stride, PixelFormat.Format24bppRgb, pBuffer))
    {
        LiveImage.RotateFlip(RotateFlipType.RotateNoneFlipY);
        if (ExpImg) // local bool, used rarely when the picture saving is triggered
        {
            var a = LiveImage.Clone(new Rectangle(Currect.Left, Currect.Top, Currect.Width, Currect.Height),
                                    LiveImage.PixelFormat);
            using (a)
                a.Save("ocr.bmp", ImageFormat.Bmp);
        }
    }

    return 0;
}

Bitmap is an Image class, and implements the IDispose. As you create Bitmap each time, I suggest to use using statement for automatically freeing the resources.