Hey, thewump, it's possible that the printer itself is somehow able to make the mental switch between B&W text and RGB graphics/photos, I'm not familiar with the internal operation of the MX870 firmware. I suppose it could.
But generally in the past on most printers, this exists as a user controlled setting you can alter in a dialog through the Print function in any particular application, Like Open Office Write, for instance.
Also in some cases you would like to print a B&W version of a color photo or color document to save color ink. So the ability to specify is usually present in most printer drivers. These get passed on to CUPS, and to applications. I'm afraid that this choice is not present in the Canon driver for this printer.
One way to check it out is to open CUPS by typing localhost:631 in your browser. Then go to the manage printers section and click on the MX870's printer's Options (or "Configure Printer) depending on your version of CUPS (not Modify printer). This will show you what options are available.
I don't see much there on mine. When I click on the drop down for "Color Model" there is only "RGB" and for resolution, there is only "600DPI".
By contrast most other brand printers drivers include grayscale, B&W, various resolution modes and possibly a number of other printer color adjustment controls.
I guess one other way of telling if text uses a mixed ink black from the small tanks, or real pigment black from the main tank is to see how fast the color ink tanks are used up vs. the black ink tank.
Do remember, all tanks are used for head cleaning (a major usage of ink) so even if black is not being used on text printout, some black will be used up by normal printer operation. It wouldn't appear as no usage of the black therefore.
If you are performing many color ink changes and just a few black tank changes, this might be what is happening. You are just using up the black for head cleaning.
On the other hand if you are changing all tanks at roughly the similar interval (for everyday mixed text use), then I guess the printer is able to distinguish and to use pigment black for text automatically.
It still would be important to be able to specify B&W as a default, even for photos, and color only when asked for, unless you do a lot of color work. Pigment black is much cheaper. Color should last a long time that way unless you do a lot of color printing.
Thanks for this thread BTW, this has nothing to do with the assistance you've given in getting the MX870 to print at all in Linux. Very helpful. This problem, if it exists, is part of the Canon driver itself.
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