Canon Pixma MG6821 Online Manual page 723

Reducing show-through in text documents or lightening the base color in
recycled paper, newspapers, etc. when scanning documents
Set Reduce Show-through to ON.
OFF
Sharpening slightly out-of-focus images
Set Unsharp Mask to ON.
OFF
Reducing gradations and stripe patterns
Set Descreen to ON.
OFF
ON
ON
ON
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