Printing in black and white without intermediate greys I'd like to routinely print using only black ink when colour isn't important, because I have a whole lot more black ink than colour ink. I have a Canon printer and I have selected the 'Black &amp; White' option from the print dialogue, but the result is that it prints in grey-scale, and the greys are rendered using the colour inks.

To prove this I scanned a printout at 600dpi and got the following in what looked like a light-grey part of the page:



I suspect that if I can convert the image to pure black and white with dithering (no grey) then the printer might then use only the black ink.  How can I do this easily from any application?  Or, how else might I configure my printer to print using only black ink?

I think there used to be filter options available in earlier versions of OS-X, which might have included something which would do this, but I don't see those anymore.



update: experimenting with Frizlab's suggestion to use the black and white Quartz filter in Preview's PDF save dialogue, I quickly realised that I was still going to have a problem with images.  Even after these become black and white bitmaps, they'll still need to be scaled to the print resolution.

As anticipated, this results in the black-and-white image being scaled with smoothing, resulting in intermediate greys which the printer renders in colour ink.  In fact, on printing my perfectly black and white test page my yellow ink lever dropped by another bar.

I also found that even perfectly black text has colour fringes on it.  I thought this might be a result of the medium-quality print setting (perhaps scaling was involved), so I printed again in high quality:

 

Even the high-quality image on the right shows a few of coloured spots (eg., top right edge), and I wonder if the difference is simply that the black has over-printed the coloured ink more thoroughly in the high-quality case.

I thought those colour spots might be aliasing or encoding artefacts, so I scanned a laser-printed page and found no such issues.

Remember that I'm not being picky about how this looks.  I just don't want to waste money replacing all my colour ink all the time while the black cartridge still has plenty of usable ink.

After this investigation, I think what I need is:


a dithering conversion, so that low-contrast text and images are visible
a conversion which matches the printer resolution exactly so that there is no scaling
to use the high-quality print setting


Or I need an alternative printer driver or printer firmware.
To convert easily any image in Black &amp; White (no gray):


Open the file in Preview
Choose "Save As…" (Visible in the File menu, while holding the Alt key in Mountain Lion)
In the save dialog, choose the PDF file format
Still in the dialog, apply Quartz filter: "Black &amp; White"




EDIT: You can convert to black &amp; white with dithering using The Gimp (free &amp; open-source):


Open the image using The Gimp
Select menu item Image -> Mode -> Indexed…
On the window that opens:


Select the Black &amp; White palette
Select a dithering mode (I chose Floyd-Steinberg)



You can also use Photoshop using the same technique. However, Photoshop is expensive.

Finally, command-line solutions exist: convert (part of the imagemagick package), or gm (part of the graphicsmagick package).