Sharp MX-3610N User Manual page 757

If [High Compression/PDF] is specified, the resolution cannot be changed in the
scanner mode. The resolution is set to 300 x 300 dpi.
If [PDF/High Compression] is set when a resolution setting has been specified in
scanner (or other) mode, the resolution setting will be cancelled and the High
Compression PDF resolution will be used for transmission.
When [PDF/High Compression] is selected, [Resolution] cannot be changed
while waiting for the next original or in [Change Setting] in the job build settings.
If [PDF/High Compression] is set when an original type setting has been
specified in scanner (or other) mode, [Photo] will change to [Text/Photo] and
[Map] will change to [Text/Printed Photo].
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