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Convert color PDF to black and white #

After exhausting the usual suspects (Adobe Acrobat, ImageMagick, Ghostscript, etc.), stumbled onto the cleanest results and smallest file size by pairing Preview.app and IrfanView:

1. Open color.pdf (96.9MB) in Preview.app
   • Remove any unwanted pages (Cmd-Delete)
   • File → Export...
   • Export As: bw.pdf
   • Format: PDF
   • Quartz Filter: Black & White
   • Save
2. Open bw.pdf (235.4MB) in Preview.app
   • File → Export...
   • Export As: bw.tif
   • Format: TIFF
   • Compression: LZW (CCITT is not available in Preview 11)
   • Resolution: 150 pixels/inch
   • Save
3. Open bw.tif (109.5MB) in IrfanView
   • File → Save as...
   • File name: bw2.tif
   • Save as type: TIF - Tagged Image File Format
   • TIFF save options → Save Compression: → CCITT Fax 4
   • Save
4. Open bw2.tif (3.9MB) in IrfanView
   • File → Save as...
   • File name: bw2.pdf
   • Save as type: PDF - Portable Document Format
   • PDF save options → Compression: → Monochrome → CCIT - Fax
   • Save (result was just 4MB)

Update

Substituting convert and gs for steps 3 and 4 led to cleaner output in some cases, albeit at the expense of larger file sizes:

$ convert bw.tif bw2.pdf
$ gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH -sOutputFile=bw3.pdf bw2.pdf

Notes

• Resolved this error:

  convert-im6.q16: cache resources exhausted `bw.tif' @ error/cache.c/OpenPixelCache/4095.
  convert-im6.q16: no images defined `bw2.pdf' @ error/convert.c/ConvertImageCommand/3229.

  by increasing the values for memory and disk in /etc/ImageMagick-6/policy.xml from these defaults to several GiBs each:

  <policy domain="resource" name="memory" value="256MiB"/>
  <policy domain="resource" name="disk" value="1GiB"/>

• The gs options used:

  • -sDEVICE=pdfwrite: Tells Ghostscript to output a PDF.
  • -dCompatibilityLevel=1.4: Sets the compatibility level of the output PDF.
  • -dPDFSETTINGS=/ebook: This setting balances quality and file size; use /screen for lower quality and smaller file size, or /prepress for higher quality at the expense of larger file size.
  • -dNOPAUSE -dQUIET -dBATCH: These options run Ghostscript in batch mode without pausing between pages.
  • -sOutputFile=bw3.pdf: Specifies the name of the output file.
  • bw2.pdf: The input PDF file.

/misc | Apr 15, 2021

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