Epson Perfection 610 User Manual page 55

The quality of an enlarged image is worse than when it's scanned at its original size.
Problem
You didn't increase
your Resolution setting
to compensate for the
image enlargement.
Moiré (crosshatch) patterns appear in the scanned image.
Problem
You have scanned a
document with halftone
patterns.
Troubleshooting
Solution
If you plan to enlarge your image by scaling, be sure to increase the
Resolution setting by the same proportion to retain your image quality.
For example, if you select 300 dpi as the resolution setting for an image
scanned at 100% of its original size and then scale the image 200%, you
should increase (in this case, double) the resolution to 600 dpi to retain
the same image quality. See
changing the Resolution setting.
For additional information on selecting scanning resolution, see your
Scanner Basics book.
Solution
To minimize moiré patterns, try the following:
Place a transparent sheet between the document and the document
table to slightly unfocus the image.
Move or angle the document slightly.
Make sure De-screening is selected in the Effect box. See
Selecting Settings
Selecting Settings
for details.
for instructions on
Page 55