---
title: Make PDF files smaller
subtitle: Convert to grayscale and reduce the resolution.
date: 2019-01-05
tags:
- PDF
---

The most effective ways of reducing the file size of a PDF is by converting to grayscale and reduce the resolution.

Requirement: ghostscript (installed by default in Ubuntu)

## Single PDF

Save the following script as "pdfcompress.sh".

Usage: `sh pdfcompress.sh input.pdf`

The output compressed file is named as "input.compressed.pdf"

```bash
#!/bin/sh

filename=$(basename "$1")
dir=$(dirname "$1")

gs \
	-sOutputFile="$dir/${filename%.*}.compressed.pdf" \
	-sDEVICE=pdfwrite \
	-dPDFSETTINGS=/ebook \
	-sColorConversionStrategy=Gray \
	-sColorConversionStrategyForImages=/Gray \
	-dProcessColorModel=/DeviceGray \
	-dCompatibilityLevel=1.4 \
	-dNOPAUSE -dBATCH -dQUIET \
	"$1"
```


Options ([more info](https://ghostscript.com/doc/current/Ps2pdf.htm#Options)):

- Remove **ColorConversionStrategy**, **ColorConversionStrategyForImages** and **ProcessColorModel** lines to retain colour.
- **PDFSETTINGS**:
	- */default* selects output intended to be useful across a wide variety of uses. 72 DPI.
	- */screen* selects low-resolution output similar to the Acrobat Distiller "Screen Optimized" setting. 72 DPI.
	- */ebook* selects medium-resolution output similar to the Acrobat Distiller "eBook" setting. 150 DPI.
	- */printer* selects output similar to the Acrobat Distiller "Print Optimized" setting. 300 DPI.
	- */prepress* selects output similar to Acrobat Distiller "Prepress Optimized" setting. 300 DPI.

## PDFs in a folder

Use the following script to compress all PDFs in a folder.

Usage: `sh pdfcompress.sh 'target folder'`

```bash
#!/bin/sh

cd "$1"

for i in *.pdf; do
    [ -f "$i" ] || break

	# Skip compressed PDFs
	echo "$i" | grep --quiet ".compressed.pdf"

	if [ $? = 1 ]
	then
		gs \
			-sOutputFile="${i%.*}.compressed.pdf" \
			-sDEVICE=pdfwrite \
			-dPDFSETTINGS=/ebook \
			-sColorConversionStrategy=Gray \
			-sColorConversionStrategyForImages=/Gray \
			-dProcessColorModel=/DeviceGray \
			-dCompatibilityLevel=1.4 \
			-dNOPAUSE -dBATCH -dQUIET \
			"$i"
	fi
done
```

<br/>
Source: [Internal Pointers](https://www.internalpointers.com/post/compress-pdf-file-ghostscript-linux), [firstdoit](https://gist.github.com/firstdoit/6390547), [ahmed-musallam](https://gist.github.com/ahmed-musallam/27de7d7c5ac68ecbd1ed65b6b48416f9), [Ghostscript Docs](https://ghostscript.com/doc/current/Ps2pdf.htm)