Dealing with white text on colored background when prepping PDFs for grayscale or B&W

JawadLeLogeur · 10-24-2025, 11:13 AM

This is mostly so that I can print a bunch of docs on my grayscale printer without using too much toner.

I've already found a number of solutions to convert a color PDF into pure B&W (as opposed to grayscale) which is ideal when the file only contains dark text on light background.

I'm running into issues when dealing with PDFs that feature BOTH color/000000 text on light/FFFFFF background and light/FFFFFF text on color/000000 background. The threshold function preserves the former as 000000 on FFFFFF but turns the latter into FFFFFF on 000000 which wastes a ton of toner. If I set the threshold too low, the text simply disappears. I can tweak grayscale of course, but it still leaves a ton of background grey that is not necessary. I will have to deal with close to a thousand pages so this is significant.

I'm looking for a method that can turn both portions that are light/FFFFFF text on color/000000 background and those that are color/000000 text on light/FFFFFF background into dark grey/000000 text on FFFFFF background.

It's okay if the end result looks nasty as long as the information on the page is legible. I can do conversions manually but if there is a way to batch these that would be awesome as well.

Quoth · 10-24-2025, 03:51 PM

k2pdfopt https://www.mobileread.com/forums/sh...d.php?t=144711

Imagemagick

also recent versions of the GIMP can import PDF pages -> layers and export layers -> pages

rkomar · 10-26-2025, 11:06 AM

This is a tough but interesting problem. After some googling, I came upon a python implementation of the algorithm produced by Grundland and Dodgson (https://github.com/damondpham/decolorize-RGB2grayscale). I haven't tried it, but it looks promising. It probably doesn't do anything about saving toner, so maybe you can make simple adjustments first before converting the image with this algorithm. Good luck!

10-24-2025, 11:13 AM	#1
JawadLeLogeur Zealot Posts: 108 Karma: 7156 Join Date: Jun 2017 Location: Western Sahara Device: Kobo Forma 4.15.12920	Dealing with white text on colored background when prepping PDFs for grayscale or B&W This is mostly so that I can print a bunch of docs on my grayscale printer without using too much toner. I've already found a number of solutions to convert a color PDF into pure B&W (as opposed to grayscale) which is ideal when the file only contains dark text on light background. I'm running into issues when dealing with PDFs that feature BOTH color/000000 text on light/FFFFFF background and light/FFFFFF text on color/000000 background. The threshold function preserves the former as 000000 on FFFFFF but turns the latter into FFFFFF on 000000 which wastes a ton of toner. If I set the threshold too low, the text simply disappears. I can tweak grayscale of course, but it still leaves a ton of background grey that is not necessary. I will have to deal with close to a thousand pages so this is significant. I'm looking for a method that can turn both portions that are light/FFFFFF text on color/000000 background and those that are color/000000 text on light/FFFFFF background into dark grey/000000 text on FFFFFF background. It's okay if the end result looks nasty as long as the information on the page is legible. I can do conversions manually but if there is a way to batch these that would be awesome as well.

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10-24-2025, 03:51 PM	#2
Quoth Still reading Posts: 14,954 Karma: 110908135 Join Date: Jun 2017 Location: Ireland Device: All 4 Kinds: epub eink, Kindle, android eink, NxtPaper	k2pdfopt https://www.mobileread.com/forums/sh...d.php?t=144711 Imagemagick also recent versions of the GIMP can import PDF pages -> layers and export layers -> pages

10-26-2025, 11:06 AM	#3
rkomar Wizard Posts: 3,065 Karma: 18821071 Join Date: Oct 2010 Location: Sudbury, ON, Canada Device: PRS-505, PB 902, PRS-T1, PB 623, PB 840, PB 633	This is a tough but interesting problem. After some googling, I came upon a python implementation of the algorithm produced by Grundland and Dodgson (https://github.com/damondpham/decolorize-RGB2grayscale). I haven't tried it, but it looks promising. It probably doesn't do anything about saving toner, so maybe you can make simple adjustments first before converting the image with this algorithm. Good luck!