FAQ: Why isn't my image the correct physical size even though UseDpi = true?

The LEADTOOLS .NET RasterImageViewer control's UseDpi property is designed to make the image display proportionally to the screen's resolution.  By default, Windows uses 96 for its screen resolution.  However, the screen resolution doesn't always match up with the physical world because different size screens can display the same number of pixels.  The result of this can mean that even though you have an image correctly sized to 8.5 x 11 inches, on the screen it might be more like 10 x 13 inches.
 
For example, the native resolution for both a 17" 4:3 monitor and a 19" 4:3 monitor are typically 1280x1024 which means the pixels are physically larger on the 19" monitor.  Therefore the actual physical resolution of the monitors are 84.2 x 89.9 for the 19" and 94.1 x 100.4 for the 17".

There are two ways you can work around this issue (in order of recommendation):

1.
Adjust the X and Y scale factors of the viewer to match the proper display.  For this, you will need to set UseDpi to false and then do something like this:

double dAspectDiagonal, dAspectWidth, dAspectHeight,
    dPhysicalDiagonal, dPhysicalWidth, dPhysicalHeight,
    dPhysicalXRes, dPhysicalYRes;

dPhysicalDiagonal = 23;
dAspectWidth = 16;
dAspectHeight = 9;

dAspectDiagonal = Math.Sqrt(Math.Pow(dAspectWidth, 2) + Math.Pow(dAspectHeight, 2));

dPhysicalHeight = (dAspectHeight / dAspectDiagonal) * dPhysicalDiagonal;
dPhysicalWidth = (dAspectWidth / dAspectDiagonal) * dPhysicalDiagonal;

dPhysicalXRes = Screen.PrimaryScreen.Bounds.Width / dPhysicalWidth;
dPhysicalYRes = Screen.PrimaryScreen.Bounds.Height / dPhysicalHeight;

rasterImageViewer1.CurrentXScaleFactor = dPhysicalXRes / rasterImageViewer1.Image.XResolution;
rasterImageViewer1.CurrentYScaleFactor = dPhysicalYRes / rasterImageViewer1.Image.YResolution;

This is a relatively new feature, so you will need to make sure you are using at least Leadtools.Winforms.dll 16.5.5.4 or 15.0.1.22.  If you do not have these builds, please contact support@leadtools.com in order to get the download instructions for the latest patch.  For verification purposes, I need you to include the following information:

- The company you work for
- The LEADTOOLS serial number(s) you own (if you are evaluating, just say so)
- The name(s) of the developer(s) using the serial number
- A link to this forum post

2.
If you want to set UseDpi to true, you can at least get the horizontal dimension correct by using Windows' advanced display settings to calibrate your monitor as shown in the screenshot attached screenshot.