You make changes in the page.xaml.cs file.
ViewportWidth
The width of the area of the image displayed. This value is in logical coordinates. For example, a value of 1 displays the entire image (no zoom), a value of 0.5 is 200% zoomed in, and a value of 0 is completely zoomed (user cannot see the image at all). A value above 1 is zooming out from the image. For example, a value of 2 means that the image will take up half the size of the
MultiScaleSubImage control area (50% zoom).
The ViewportOrigin
X (-0.02456985) = The left coordinate of the rectangular area of the image to be displayed. The coordinates of the point are in local coordinates (0-1) relative to the displayed image width.
Y (-0.35426895) = The top coordinate of the rectangular area of the image to be displayed. The coordinates of the point are in local coordinates (0-1) relative to the displayed image width.
void msi_ImageOpenSucceeded(object sender, RoutedEventArgs e)
{
this.msi.ViewportWidth = 0.5;
this.msi.ViewportOrigin = new Point(-0.02456985, -0.035426895);
ZoomFactor = 0.5;
}
See further:
http://msdn.microsoft.com/en-us/library/cc645050(VS.95).aspx