Canon IMAGERUNNER C2550 Printer Manual page 240

NOTE
You can also perform the same procedure from the touch panel display. (See "Line
Control," on p. 3-20.)
Gradation in the black or gray parts of the image does not appear smooth (the color changes
stand out).
Cause
Remedy
IMPORTANT
If you change the above settings, gray or black data is printed using CMYK toners.
Therefore, the data may be printed in color, even if all pages are monochrome.
NOTE
You can also perform the same procedure from the touch panel display. (See "RGB Pure
6
Black Process," on p. 3-71.)
The gray data appears grainy.
Cause
Remedy
IMPORTANT
If you change the above settings, gray or black data is printed using CMYK toners.
Therefore, the data may be printed in color, even if all pages are monochrome.
NOTE
You can also perform the same procedure from 'RGB Pure Black Process' or 'Output
Profile' in the touch panel display. To perform the 'Output Profile' setting, set to [Normal].
(See "RGB Pure Black Process," on p. 3-71, and "Output Profile," on p. 3-69.)
6-24
Printing Problems
'RGB Pure Black Process' is affecting the black or gray part of the gradation.
Disable 'RGB Pure Black Process' in the Windows PS printer driver or Mac PS
printer driver and print the data again. (See the Help function on the printer
driver.)
The RGB Pure Black Process setting, in combination with the Prioritize Printing
of Lines and Text setting in the printer driver or Output Profile setting on the
control panel, is affecting the gray part of the data.
Disable 'RGB Pure Black Process' and 'Prioritize Printing of Lines and Text' in
the Windows PS printer driver or Mac PS printer driver, and print the data again.
(See the Help function on the PS printer driver.)