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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 & 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:

Black & White print-out close-up

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:

black letter 'a' close-up enter image description here

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.

  • 3
    Now that is an awesome scan showing a non-obvious result when you tell a printer to convert a color image to greyscale. – bmike Oct 20 '13 at 2:38
  • 1
    Ohhhhh, so THAT'S why you can't print a grayscale document when you're out of color ink! – Blacklight Shining Oct 20 '13 at 3:22
  • So I just found that Adobe Acrobat Reader DC has an advanced option "Treat grays as K-only grays", and I tried this and I got no colour dots in scan. If I find time I'll answer my own question with some scans and details on what I can find on the setting... but "K-only" sounds like the thing to look for. – sh1 Oct 12 '15 at 2:02
4

To convert easily any image in Black & 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 & White"

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

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

    • Select the Black & 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).

  • This is a very good start, but unfortunately it's strict black-and-white without dither. The result is that when printing out a web page (eg., this page) light text disappears completely, and dark backgrounds turn completely black. – sh1 Oct 20 '13 at 18:11
  • I added a solution to convert to black & white w/ dithering. Note you can convert your image to the resolution of your printer before doing the black & white conversion. – Frizlab Oct 21 '13 at 7:34
  • I can add the command-line solutions in the answer if you need them. – Frizlab Oct 21 '13 at 7:35
  • You have to rememer to select high resolution (even 1200) when you import your PDF and use dithering during conversion to 1 bit image. If the printout is too dark, you can try to use curves tool or change brightness before conversion. It would be nice to have a script or application that would do it automatically for entire PDF. A lot of people unconsciously print simple B/W documents such as invoices with all colors. – Jupiter Feb 15 '18 at 13:11

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