Thank you for contacting us and sorry for the late reply.
The problem with the Stretch="UniformToFill" property is that the initial zoom applied to the image is from the grid, not from the PanAndZoomImage control. You can achieve the desired effect by setting a proper Zoom property depending on the image size. You can use the ImageOpened event to calculate the new Zoom factor:
sender, RoutedEventArgs e)
var image = sender
.LayoutRoot.ActualWidth / image.ActualWidth;
.LayoutRoot.ActualHeight / image.ActualHeight;
.PanZoomImage.Zoom = Math.Max(horizontalZoom, verticalZoom);
I hope this helps. Please, let us know if you have further questions.
Check out the Telerik Platform - the only platform that combines a rich set of UI tools with powerful cloud services to develop web, hybrid and native mobile apps.