Scanned Image Is Of Uneven Quality - Canon S400 Reference Manual

Scanned image is of uneven quality

The scanned image is coarse and blurry.
Check
Is the resolution setting high enough?
Resolution determines the precision of the scanned image.
The greater the number of dots used to draw an image, the greater the pre-
cision and the higher the quality of the scanned image. For a better quality
image, select a high number.
Note that the scanning speed becomes slower and the file size of the
scanned image becomes larger when you use a higher resolution.
Troubleshooting - Scanning result is unsatisfactory 222