Canon MG8100 series On-Screen Manual page 744

3.
Click Preview.
When Photo or Document is Previewed
Preview image appears in the Preview area.
Note
Colors are adjusted based on the document type selected in Select Source.
When Film is Previewed
Preview images appear in the Preview area. Images are cropped (scan areas are specified)
automatically according to the film size.
Select the frames to scan.
Important
Film cannot be scanned without previewing.
4.
Set Destination.
5.
Set Output Size.