WPF Image displays smaller than when viewed in external viewer

Question

When I display a JPEG in my WPF application (using the following code), it is shown significantly smaller than if I open the JPEG in the Windows Picture Viewer at actual size.

I've drilled into the properties of my ImageSource at runtime and my image has:

• a DPI of 219
• a Height of 238.02739726027397
• a Width of 312.54794520547944
• a PixelHeight of 543
• and a PixelWidth of 713

When I use a screen ruler to measure the WPF display of the image, I get approx. 313x240 pixels (which if I could positiont the ruler perfectly would probably be equal to the Width and Height that the ImageSource is reporting.).

My gut tells me this has something to do with WPF's use of device independent units (instead of pixels) but I can't make sense of it, and I still need to know how to display the image at the 'actual' size of 543x713 in my application.

<Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Height="300" Width="300">
    <StackPanel>
     <Image Source="Image15.jpg" Stretch="None" />
    </StackPanel>
</Window>

Answer 1

Use a DPI of 96. WPF is scaling your image based on the size in inches, while the image viewer is displaying pixels. On most Windows systems, the screen resolution is assumed to be 96 DPI, so using that in your image will result in a one-to-one translation.

Answer 2

This is the result of the .jpg file itself specifying the DPI - WPF is simply obeying. Here is a forum post detailing the problem with some solutions:

Answer 3

Thanks Mark! I did some Googling based on your info and found this article that provided a solution to get the result I wanted. This is starting to make sense now...