wpf bind property to resize bmp in hight dpi

Having to display bitmap images - not vector at several user's dpi settings in a XBAP WPF application, I'd like to setup a dpiFactor global variable at startup, that will be calculated as a percentage of the original bitmSizeap:

i.e. for 120 dpi I want both size of the image to be: newSize = originalSize * (100 - (120 - 96)) / 100 which means multiply by 75% if the dpi i开发者_StackOverflow中文版s 125% of original.

The dpiFactor have to be defined at startup, and then all measurement to be scaled down (or up) when page is launched. How can I express that in XAML perhaps with a bound property?

Maybe you can use a converter that looks like this:

  [ValueConversion(typeof(string), typeof(BitmapImage))]
  public class ImageConverter : IValueConverter
  {
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
      string imageSource = value as string;
      if (imageSource == null)
        return DependencyProperty.UnsetValue;

      try
      {
        BitmapImage originalImage = new BitmapImage(new Uri(imageSource));
        int originalWidth = originalImage.PixelWidth;
        int originalHeight = originalImage.PixelHeight;

        double originalDpiX = originalImage.DpiX;
        double originalDpiY = originalImage.DpiY;

        BitmapImage scaledImage = new BitmapImage();
        scaledImage.BeginInit();
        scaledImage.DecodePixelWidth = originalWidth; // Place your calculation here,
        scaledImage.DecodePixelHeight = originalHeight; // and here.
        scaledImage.UriSource = new Uri(imageSource);
        scaledImage.EndInit();
        scaledImage.Freeze();

        return scaledImage;
      }
      catch
      {
      }
      return new BitmapImage();
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
      throw new NotImplementedException();
    }
  }

And in xaml this will looks like this:

<Window x:Class="Test.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:test="clr-namespace:Test">
  <Window.Resources>
    <test:ImageConverter x:Key="imageConverter" />
  </Window.Resources>
  <Image Source="{Binding SomePath, Converter={StaticResource imageConverter}}" />
</Window>

To get the system's dpi i think you can use this code.