Canon MP490 series On-Screen Manual page 505

None Auto
Sharpening slightly out-of-focus images
Set Unsharp Mask to ON.
OFF
Reducing gradations and stripe patterns
Set Descreen to ON.
OFF
Note
"Moire" is a phenomenon where uneven gradation or a stripe pattern appears when such photos or
pictures printed with fine dots are scanned. Descreen is the function for reducing this moire effect.
Reducing dust and scratches
Set Reduce Dust and Scratches to Low, Medium or High according to the degree of dust and scratches.
None
Correcting photos that have faded with time or due to colorcast
Set Fading Correction to Low, Medium or High according to the degree of fading or colorcast.
Medium
None
ON
ON
Medium