Canon BJC-6200 - Manual (Page 235)

235 Troubleshooting - Scanning result is unsatisfactory
White portion becomes greyish
Check 3 Did you scan a monochrome image using the Colour or Greyscale setting?
If the scanning mode is set to Colour or Grayscale, the scanner detects and
scans gradations evenly, and white may not be recognised as white. When
you scan a 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.