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

Question

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(BitmapFrame.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.

scaleX and scaleY are gonna be huge. It's maybe that. — Nicolas Repiquet
– Nicolas Repiquet, Commented Dec 17, 2010 at 10:55

Hans Passant · Accepted Answer · 2010-12-17 11:56:51Z

3

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

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

answered Dec 17, 2010 at 11:56

Hans Passant

946k151 gold badges1.8k silver badges2.6k bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Hans Passant Over a year ago

You changed your question. This answer tells you why you got the exception, your original question.

Jonas Van der Aa Over a year ago

Oh right, my bad, I seem to loose track of that sometimes, I'll change it back and open a new topic :)

Jon Skeet · Accepted Answer · 2010-12-17 10:55:59Z

1

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.

answered Dec 17, 2010 at 10:55

Jon Skeet

1.5m893 gold badges9.3k silver badges9.3k bronze badges

1 Comment

Jonas Van der Aa Over a year ago

I changed it to that but now I get images that are 1 x 1 and black (1 black pixel).

Collectives™ on Stack Overflow

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

2 Answers 2

2 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related