What is causing a OverflowException on TransformedBitmap.EndInit when trying to scale a bitmap in WPF?

I have the following code:

private void Process(string path)
    {
        using (FileStream fs = File.OpenRead(path))
        {
            JpegBitmapDecoder decoder = new JpegBitmapDecoder(fs,BitmapCreateOptions.PreservePixelFormat,BitmapCacheOption.Default);
            BitmapSource bmps = decoder.Frames.First();
            double targetScale = 800.0/600.0;
            double scaleX = bmps.PixelWidth*targetScale;
            double scaleY = bmps.PixelHeight*targetScale;
            TransformedBitmap tbmp = new TransformedBitmap();
            tbmp.BeginInit();
            tbmp.Source = bmps;
            tbmp.Transform = new ScaleTransform(scaleX, scaleY);
            tbmp.EndInit();
            JpegBitmapEncoder encoder = new JpegBitmapEncoder();
            encoder.Frames.Add(Bit开发者_如何学编程mapFrame.Create(tbmp));
            using (FileStream fs2 = File.OpenWrite(path+".jpg"))
            {
                Debug.WriteLine(path+".jpg");
                encoder.Save(fs2);
            }
        }
    }

It throws an OverflowException at tbmp.EndInit();

Any idea why?

UPDATE: It might be worth mentioning that this method is called through a ParallelQuery. It doesn't depend on anything that could be in a different thread though.

You already calculated the required scaling, 800/600. Don't multiply by the image size. Fix:

  tbmp.Transform = new ScaleTransform(targetScale, targetScale);

My guess is that it's because your scale is huge. For example, suppose the original picture is 1600x1200... you're then scaling it by a factor of 2,133.33333x1600, giving you a final picture size of 3,413,333 x 1,920,000 - which is a pretty huge picture!

I suspect you wanted:

double scaleX = targetScale / bmps.PixelWidth;
double scaleY = targetScale / bmps.PixelHeight;

After all, I assume that if the original picture is bigger, you want to stretch is less, not more.