Canon PIXMA MG4200 Series On-Screen Manual page 651

Gutter shadow will not be corrected.
Low
Select this when the effect level is too strong with the medium setting.
Medium
It is recommended that you normally select this setting.
High
Select this when the effect level is too weak with the medium setting.
Important
Do not place items that weigh 4.4 lbs (2.0 kg) or more on the Platen. Also, do not press on the
document with a force exceeding 4.4 lbs (2.0 kg). If you press heavily, the scanner may not work
correctly or you might break the glass.
Align the document with the edge of the Platen. If not, the shadow will not be corrected properly.
Shadows may not be corrected properly depending on the document. If the page background is not
white, shadows may not be detected correctly or may not be detected at all.
While scanning, press down on the spine with the same amount of pressure you used to preview
the scan. If the binding part is not even, the shadow will not be corrected properly.
How to place the document depends on your model and the document to be scanned.
Note
Cover the document with black cloth if white spots, streaks, or colored patterns appear in scan
results due to ambient light entering between the document and the Platen.
If the shadow is not corrected properly, adjust the cropping frame (scan area) on the preview
image.
Adjusting Cropping Frames
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