Grayscale PDF

Converting to grayscale isn't a matter of telling viewers to display a page without color — it works by rendering each page and replacing its actual pixel values with gray equivalents, discarding the separate red, green and blue channel data entirely. That's a real, permanent change to the file's content, distinct from simply choosing 'print in black and white' from a printer dialog, which leaves the underlying document completely untouched and just changes how it comes out of the printer.

This is useful before sending a document to a black-and-white printer, where the print shop or office printer may otherwise interpret color content oddly or charge color-page rates, and for accessibility or consistency purposes where uniform contrast matters more than color accuracy.

Because rasterizing is part of how this works, the same tradeoffs as compression apply: text stops being selectable, and a page that was mostly clean vector text to begin with may not shrink at all — it can even grow slightly, since flat text now has to be stored as image pixels instead of compact text operators. The clearest wins show up on documents with color images or scanned color pages, where dropping to grayscale meaningfully reduces the data needed per pixel.