Canon BJC-3000 - Manual (Page 283)

283 Troubleshooting - Scanning result is unsatisfactory
White portion becomes greyish
Check 3 Did you scan a monochrome image using the Colour or Grayscale setting?
If the scanning mode is set to Colour or Grayscale, the scanner detects and
scans even the grades of the density, and white may not be recognised as
white.
When you scan the monochrome image, always set Black & White in the
scanning mode so the scanner can scan using only two values between
white and black.
For details on how to set Black and White in the scanning mode, refer to the
on-line Help.