How Do I Convert a PDF to Black and White?

What does "convert a PDF to black and white" actually mean?

For nearly everyone, converting a PDF to black and white means stripping out color so the page prints or displays in shades of gray, not pure black or pure white pixels.

• Grayscale: each pixel can be one of up to 256 shades between black and white, so photos, shadows and highlights still look smooth.
• Bitonal (true black and white): each pixel is only ever fully black or fully white, with no shade between them.
• Most document scanning guides treat grayscale as 8 bits of data per pixel and bitonal as 1 bit, which is why a bitonal page is so much smaller to store.
• When someone asks for a "black and white PDF," they almost always mean the grayscale kind, since that's what every major PDF tool actually builds.

Why does my "black and white" PDF still show shades of gray?

It still shows gray because the conversion tool, and often the printer too, is working in grayscale rather than true bitonal.

• Smooth edges on text and lines are drawn with partial gray pixels so they don't look jagged, which reads as gray even on a page meant to be plain black ink.
• A printer's "Black & White" setting usually behaves like grayscale in practice, building tone from a mix of ink rather than printing pure black dots.
• Scanned photos and colored highlighters turn into mid-gray blocks instead of disappearing, because grayscale keeps the brightness of the original color.
• People searching for a way to get "black and white, not grayscale" are really asking for bitonal, which most online converters don't offer at all.

How do I convert a PDF to black and white with VelloDoc?

Upload the file to Grayscale PDF and run the conversion. There are no settings to pick, so the whole document comes back in shades of gray.

• Add the color PDF and select Convert to Grayscale, then download the result.
• When the server has Ghostscript available, the page is rewritten with gray colors in place of the original ones, so text stays text and stays searchable.
• Without Ghostscript, the tool falls back to rendering each page as a gray image at 150 dpi, which keeps the look but turns the text into a picture.
• If you hit that fallback and need the words searchable again, run the file through OCR PDF afterward to put selectable text back on the page.
• Check charts and highlighted text once it's done: colors that only differ in hue, like red and green, can turn into nearly the same gray.

Should I use grayscale or true black and white?

Grayscale is the right choice for almost everything you'd convert a PDF for; true bitonal black and white only makes sense for plain typed text you want as small as possible.

• Grayscale is right for: photos, scanned forms with signatures, charts and anything where you still want to tell light gray from dark gray.
• A 2023 Pennsylvania State Archives guideline sets 8 or 16 bit grayscale for typed text pages, but calls for full 24 bit color on handwritten ones, since gray loses faint pen strokes.
• US federal rules for digitizing paper records, at 36 CFR 1236.50, set grayscale at a bit depth of 8 or 16, the same 256 or 65,536 shade range most office scanners use.
• Bitonal is right for: dense, plain text pages scanned purely to save space, where you don't need any gray tone and losing it isn't a problem.
• If file size matters more than the look, convert to grayscale first with Grayscale PDF, then run Compress PDF for a smaller file, instead of hunting for a bitonal tool.

Does converting to black and white shrink the file?

Often yes, because a gray pixel only needs one number instead of three, so a scanned color page can drop a lot of its raw data once it's gray.

• A color pixel is usually stored as three numbers, for red, green and blue. A gray pixel only needs one, so raw image data shrinks by about two thirds before compression runs.
• The saving is biggest on scanned pages and photos. A PDF made from text and vector shapes was already small, so turning it gray barely changes the file size.
• If the gray version still feels too big, especially after a scan, Compress PDF squeezes it further on top of the grayscale pass.

Try the tools

Try it on your own file. The tools are free and you don't need an account.