Canon i 850 User Manual page 139

Set the halftoning method to Diffusion in the printer driver settings.
Windows
1
Open the Printer Properties dialog box.
2
On the Main tab, select Custom for the Print Quality setting, and click Set.
3
Click Diffusion for the Halftoning setting.
Macintosh
1
Open the Print dialog box.
2
For Print Mode, select Manual and then click Details.
3
Click the Quality icon and then click Diffusion for the Halftoning setting.
Print Quality is Poor or Contains Errors
Troubleshooting
139