There are various ways to display Images in 3D, the 3 most common ways are -

1) Right click on map and View Map in 3D or Discover3D>View Map - produces lowest resolution results.

2) Discover3D>3D Utilities>Overlay Image on Grid - this preserves full input resolution from the image.

3) Directly open an Image in 3D by using File>Open and select All Supported Image types.


If you are using the View Map In 3D option, by right clicking on the MapInfo Map Window, Discover 3D is essentially taking a screen-shot of this map window, so you need to maximise the size of this view.
This resolution can be improved by -

1/. Ensure that the map window is as large as possible (without being maximised), and that the mapper
view is zoomed to just the data to be displayed (rather than being surrounded by a 'buffer' of white/empty space).

2/. In the MapInfo/Discover 2D interface, select the Discover 3D>Options menu option. Switch to the
Display tab, and increase the 'Create Raster Images at' value. Obviously increasing this value
will increase not only the quality of the output image, but also its file size, which if applied to multiple
images in 3D may reduce the efficiency of working in the 3D environment.