What it does

When copy-pasting images to PowerPoint presentations, these sometimes get inserted as lossless versions, blowing up the size of the presentation.

This script takes all PNG or TIFF images part of the presentation which are larger than a given threshold (1 MiB by default), converts them to a lossy JPEG variant, and creates a new PPTX file.

⚠️ This is not the same as compressing images with PowerPoint's own functionality. You may still need to do this to reduce the size of your presentation!

By default, PNGs containing transparency are automatically skipped to prevent graphics issues (since JPEG doesn't support transparency). If you want to force conversion of transparent images anyway, their transparent parts will be replaced with white (although you can choose another color with -t).

Requirements

Operating system: macOS or Linux
- Note: Under Linux, you need LibreOffice installed to convert embedded EMF files
Python 3.9 or higher
ImageMagick (either version 6.x with convert/identify commands or version 7.x with magick command)
Optionally: ffmpeg for media files

Under Ubuntu, get ImageMagick via:

apt install imagemagick

Under macOS, install it with Homebrew:

brew install imagemagick

For ffmpeg, use the static builds from ffmpeg.org.

Installation

Simply run it via uv:

uvx compress-pptx

Or install via pipx. Or manually via pip:

pip3 install --user compress-pptx

Usage

Call compress-pptx and point it to a PPTX or POTX file. It'll compress the images and output another compressed file next to it.

For more options, see the -h output:

usage: compress-pptx [-h] [-o OUTPUT] [-s SIZE] [-q QUALITY] [-t TRANSPARENCY]
                     [--no-skip-transparent-images] [-v] [-f] [-m] [-j] [-l]
                     [--num-cpus NUM_CPUS] [--extract EXTRACT]
                     [--ffmpeg-crf FFMPEG_CRF]
                     [--ffmpeg-video-codec FFMPEG_VIDEO_CODEC]
                     [--ffmpeg-audio-codec FFMPEG_AUDIO_CODEC]
                     [--ffmpeg-extra-options FFMPEG_EXTRA_OPTIONS]
                     [--ffmpeg-path FFMPEG_PATH]
                     input
positional arguments:
  input
options:
  -h, --help            show this help message and exit
  -o OUTPUT, --output OUTPUT
                        Output file (default: None)
  -s SIZE, --size SIZE  Minimum size threshold in bytes. Also accepts the
                        suffixes k/M/G or KiB/MiB/GiB (default: 1MiB)
  -q QUALITY, --quality QUALITY
                        JPEG output quality (0-100) (default: 85)
  -t TRANSPARENCY, --transparency TRANSPARENCY
                        Replace transparency with color (default: white)
  --no-skip-transparent-images
                        Convert transparent images to JPEG (will replace
                        transparency with background color). By default,
                        transparent images are skipped to preserve transparency.
  -v, --verbose         Show additional info (default: False)
  -f, --force           Force overwriting output file (default: False)
  -m, --compress-media  Compress other media types such as audio and video
                        (requires ffmpeg) (default: False)
  -j, --recompress-jpeg
                        Recompress jpeg images (default: False)
  -l, --use-libreoffice
                        Use LibreOffice to compress EMF files (only way to
                        compress EMF files under Linux) (default: False)
  --num-cpus NUM_CPUS   Number of CPUs to use (default: all available CPUs)
  --extract EXTRACT     Extract all media from the presentation to the
                        specified directory (default: None)
  --ffmpeg-crf FFMPEG_CRF
                        FFmpeg CRF value for video encoding (e.g., 23 for
                        libx264) (default: None)
  --ffmpeg-video-codec FFMPEG_VIDEO_CODEC
                        FFmpeg video codec (e.g., libx264 for best PowerPoint
                        compatibility) (default: None)
  --ffmpeg-audio-codec FFMPEG_AUDIO_CODEC
                        FFmpeg audio codec (e.g., aac, libopus, libmp3lame)
                        (default: None)
  --ffmpeg-extra-options FFMPEG_EXTRA_OPTIONS
                        Extra FFmpeg options as a single string (e.g.,
                        '-preset slow -tune stillimage') (default: None)
  --ffmpeg-path FFMPEG_PATH
                        Path to ffmpeg executable (default: ffmpeg)

For example, to compress presentation.pptx and output to presentation-compressed.pptx with a quality of 75:

compress-pptx -o presentation-compressed.pptx -q 75 presentation.pptx

If you have ffmpeg installed, you can also compress audio and video files embedded in the presentation with the -m flag:

compress-pptx -m presentation.pptx

Transparent images are automatically skipped by default to preserve transparency. If you want to force conversion of transparent images to JPEG (replacing transparency with a background color), use the --no-skip-transparent-images flag:

compress-pptx --no-skip-transparent-images presentation.pptx

Extracting media

To extract all media files from a presentation, use the --extract option with a directory path:

compress-pptx --extract ./media presentation.pptx

This will create the media directory (if it doesn't exist) and extract all images, audio, and video files from the presentation into it.

FFmpeg encoding options

When using -m to compress media files, you can customize the FFmpeg encoding settings:

compress-pptx -m --ffmpeg-video-codec libx265 --ffmpeg-crf 34 presentation.pptx

Note that the default is libx264 and CRF 23.

You can pass additional FFmpeg options using --ffmpeg-extra-options:

compress-pptx -m --ffmpeg-video-codec libx264 --ffmpeg-extra-options '-preset slow -tune stillimage' presentation.pptx

To see available options for a specific encoder, run:

ffmpeg -h encoder=libx264

Contributors

License

MIT License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.