color-to-grayscale

name	color-to-grayscale
description	Convert a color PDF to grayscale (black-and-white) for monochrome digital printing — saves toner and avoids color-mismatch issues. Triggers on phrases like "convert PDF to grayscale", "make it black and white", "remove color from PDF", "monochrome PDF".

Convert PDF to Grayscale

Strip color from every page of a PDF, producing a grayscale-only output suitable for monochrome printing.

Inputs

• Input PDF path (required).
• Output path (optional) — defaults to <input>-grayscale.pdf.

Tooling

Use ghostscript with the pdfwrite device and a grayscale color conversion strategy. This is the most reliable method — it converts both raster images and vector content.

Recipe

gs -sOutputFile=output.pdf \
   -sDEVICE=pdfwrite \
   -sColorConversionStrategy=Gray \
   -sProcessColorModel=DeviceGray \
   -dCompatibilityLevel=1.4 \
   -dNOPAUSE -dBATCH \
   input.pdf

Workflow

1. Verify input exists.
2. Confirm gs is installed.
3. Run the conversion.
4. Spot-check by rendering page 1 to PNG and confirming no color channels:

   gs -sDEVICE=png16m -r72 -o /tmp/check.png -dFirstPage=1 -dLastPage=1 output.pdf
   

5. Report file size delta — grayscale PDFs are usually significantly smaller.

Output

Grayscale PDF written to the requested path. Original is not modified.

Caveats

• If the source PDF embeds CMYK or spot colors, the conversion is still safe but may flatten subtle tones.
• Text remains crisp; embedded JPEGs are re-compressed as grayscale JPEGs.