pdfc – PDF Compressor for the Command Line

A command-line tool for compressing and optimising PDF files using configurable rasterization, colour mode, sharpening and contrast settings.

Compressing a PDF file:

Interactive mode:

Comparing compression presets:

Requirements

• Python 3.11+
• Poppler (for pdf2image)
  • macOS: brew install poppler
  • Ubuntu/Debian: sudo apt install poppler-utils

Installation

Via pip

pip install pypdfc

pypdfc on PyPI

From Source

1. Clone this repository:

   git clone https://github.com/cgroening/py-pdfc.git
   cd py-pdfc

2. Install the package if you want the pdfc command available globally:

uv pip install .

Alternatively, pdfc can be run without installation, see Section Without Installation.

Commands

compress – Compress one or more PDF files

pdfc compress [OPTIONS] INPUT_PATH [OUTPUT_PATH]

Argument / Option	Short	Description
--interactive	-i	Collect all settings interactively via prompts
--verbose	-v	Verbose output
--mode	-m	Colour mode: color, gray or bw
--dpi	-d	Resolution for rasterization in dots per inch (default: 300)
--jpeg-quality	-q	JPEG quality 1–100 (default: 30). Mutually exclusive with --png-compression-level
--png-compression-level	-p	PNG compression level 0–9 (default: 6). Mutually exclusive with --jpeg-quality
--threshold	-t	B&W threshold 0–255 (default: 150). Only used in bw mode
--sharpen	-s	Sharpening factor 0.0–3.0 (default: 0.0 = off)
--contrast	-c	Contrast factor 0.0–3.0 (default: 1.0 = no change)
--unsharp-mask	-u	Apply PIL UnsharpMask filter
--tiff-ccitt	-T	Use TIFF CCITT Group 4 as intermediate format (bw mode only)
--no-skip		Process all files, including files ending with -compressed.pdf (which are skipped by default when input is a directory)
INPUT_PATH		PDF file or directory of PDF files to compress
OUTPUT_PATH		Output file (single-file mode only). Defaults to <input>-compressed.pdf

Examples:

# Compress a single file to B&W at 300 DPI
pdfc compress input.pdf -m bw -d 300

# Compress with a custom output path
pdfc compress input.pdf output.pdf -m gray -d 200 -q 50

# Compress all PDFs in a folder using defaults (skips *-compressed.pdf files)
pdfc compress /path/to/folder

# Compress all PDFs in a folder, including already compressed files
pdfc compress /path/to/folder --no-skip

# Choose settings interactively
pdfc compress input.pdf -i

compare – Compare compression configurations side by side

Runs all presets defined in ~/.config/pdfc/presets.yaml against one or more PDF files and writes the results into a subdirectory named after each input file.

Fields:

Field name	Type	Range	Default	Description
name	string	[a-zA-Z0-9_-]+	-	Required. Used as the output file name.
mode	string	color, gray or bw	bw	Color space of the output: Black & white (1-bit after threshold conversion), Grayscale (8-bit) or Color (RGB, 24-bit)
dpi	int	> 0	300	Resolution for rasterization. Strongly affects both quality and file size.
threshold	int	0-255	150	Threshold for B&W conversion. Pixels above the value → white, below → black. Higher value = more white = smaller file.
jpeg_quality	int	1-100	30	JPEG quality. Lower values = smaller file, lower image quality. Enables JPEG mode. Cannot be combined with png_compression.
png_compression	int	0-9	7	PNG compression level. PNG compression level. Higher values lead to smaller files and longer processing times. Enables PNG mode. Cannot be combined with jpeg_quality.
sharpen	float	0.0-3.0	1.0	Sharpening filter (PIL ImageEnhance.Sharpness). 0.0 → off, 1.0 → no change, >1.0 → sharper.
contrast	float	0.0-3.0	1.0	Contrast filter (PIL ImageEnhance.Contrast). 1.0 → no change, >1.0 → more contrast.
unsharp_mask	bool	true/false	false	PIL UnsharpMask filter (radius=2, percent=150, threshold=3). Sharpens edges before conversion.
tiff_ccitt	bool	true/false	false	Use TIFF CCITT Group 4 intermediate format

pdfc compare [OPTIONS] INPUT_PATH

Option	Short	Description
--dpi	-d	Resolution for rasterization (default: 300)
--verbose	-v	Verbose output

Examples:

# Compare all presets for a single file
pdfc compare input.pdf

# Compare all presets for all PDFs in a folder at 200 DPI
pdfc compare /path/to/folder --dpi 200

Output is written to a subdirectory next to the input file:

input.pdf
input/
  preset-name-1.pdf
  preset-name-2.pdf
  ...

Usage without Installation

The package can also be run without installation from the project root:

python -m pdfc

Presets file

The compare command reads presets from ~/.config/pdfc/presets.yaml. Each preset defines a named compression configuration.

Example:

presets:
  - name: bw-300
    mode: bw
    dpi: 300
    threshold: 150
    sharpen: 1.5
    contrast: 1.5

  - name: gray-150
    mode: gray
    dpi: 150
    jpeg_quality: 40

  - name: color-200
    mode: color
    dpi: 200
    jpeg_quality: 60
    sharpen: 1.3
    contrast: 1.3

See example-presets.yaml for more presets to try.

Available preset fields:

Field	Type	Description
name	string	Required. Used as the output file name
mode	string	color, gray or bw
dpi	int	Resolution for rasterization
threshold	int	B&W threshold 0–255
jpeg_quality	int	JPEG quality 1–100
png_compression	int	PNG compression level 0–9
sharpen	float	Sharpening factor 0.0–3.0
contrast	float	Contrast factor 0.0–3.0
unsharp_mask	bool	Apply PIL UnsharpMask filter
tiff_ccitt	bool	Use TIFF CCITT Group 4 intermediate format

Compression modes

Mode	Description
color	Keeps full colour. Best for photos and colour diagrams
gray	Converts to greyscale. Good balance of size and readability
bw	Converts to black & white. Smallest file size, best for text-only scans

Parameter reference

Sharpen (-s / --sharpen)

Range: 0.0 to 3.0 (float)

Value	Effect	Use case
0.0	No sharpening (off)	Default
0.5	Slight blur	Noise reduction
1.0	Original (no change)	Baseline
1.2–1.5	Light sharpening	Recommended for clean documents
1.5–2.0	Medium sharpening	Good for text
2.0–2.5	Strong sharpening	For blurry scans
2.5–3.0	Very strong sharpening	Risk of artefacts
>3.0	Extreme (not allowed)	Too much; artefacts likely

Visual effect:

sharpen = 0.5:  T e x t   (blurry)
sharpen = 1.0:  Text      (original)
sharpen = 1.5:  Text      (crisper)
sharpen = 2.0:  Text      (very sharp)
sharpen = 3.0:  Text      (over-sharpened, halo artefacts)

Too much sharpening (> 3.0):

• Halos around letters (white/black fringes)
• Noise amplification (grainy look)
• Edge artefacts
• Unnatural appearance

Contrast (-c / --contrast)

Range: 0.0 to 3.0 (float)

Value	Effect	Use case
0.0	Flat grey (no contrast)	Not useful
0.5	Reduced contrast	Softer images
1.0	Original (no change)	Baseline
1.2–1.5	Slightly increased contrast	Recommended for clean documents
1.5–2.0	Medium contrast	Good for text, clear separation
2.0–2.5	Strong contrast	For faded documents
2.5–3.0	Very strong contrast	Risk of detail loss
>3.0	Extreme (not allowed)	Near binary; details lost

Visual effect:

contrast = 0.5:  Text  (washed out, grey)
contrast = 1.0:  Text  (original)
contrast = 1.5:  Text  (crisper, more defined)
contrast = 2.0:  Text  (very clear, strong separation)
contrast = 3.0:  Text  (near binary)

Too much contrast (> 3.0):

• Detail loss (everything becomes black or white)
• No more grey tones
• Hard edges without transitions
• Information loss

Interaction between contrast and threshold

Contrast is applied before the B&W threshold. A higher contrast value effectively makes the threshold more aggressive, since pixel values are pushed further apart before the cut-off is applied.

Scenario	contrast	threshold	Pixel at 140	Pixel at 160
Low contrast	1.0	150	stays ~140 → black	stays ~160 → white
High contrast	2.0	150	pushed to ~100 → black	pushed to ~200 → white

Rule of thumb: increase contrast only as much as needed; combine with the threshold to control where the black/white boundary falls.

Recommended combinations

Document type	sharpen	contrast	Notes
Clean, digital documents	1.3	1.3	Subtle improvement, no risk
Standard scans	1.5	1.5	Best balance
Blurry or faded scans	2.0	2.0	Strong improvement, low artefact risk
Very poor scans	2.5	2.5	Maximum recommended
Last resort	3.0	3.0	Artefacts likely

Recommended parameter ranges (summary)

Parameter	Minimum	Recommended	Safe maximum	Risky maximum
Sharpen	0.0 (off)	1.3–2.0	2.5	3.0
Contrast	0.0 (grey)	1.3–2.0	2.5	3.0

Planned features

v0.1 – Initial release

• Skip files with the suffix -compressed.pdf to avoid re-processing already compressed files, unless flag --no-skip is set
• Skip presets for color mode if input file is B&W or grayscale
• Improve/clean output messages when processing files and presets

v0.2 – Presets management

• presets.yaml: Field to set one preset as default for compress command, warn if missing or multiple defaults
• Add --preset option to compress command to specify a preset from the presets file, e.g. pdfc compress input.pdf --preset bw-300
• Add command list-presets which lets the user interactively view, add, edit and delete presets in the presets file
• Add command preset which lets the user select a preset from the presets file and applies it to one or more PDF files