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Tool for downsizing Microsoft PowerPoint pptx presentations.

Project description

Python tool for downsizing Microsoft PowerPoint presentations (pptx) files.

Currently only supports downsizing of images (not e.g. videos and other media files).

Use cases:

Why might someone want to downsize a Power Point presentation?

If you are like me, when you create a PowerPoint presentation, you just throw in a lot of images on the slides without paying too much attention to how large the images are.

You may even use the “screenshot” feature (Cmd+shift+4 on Mac) to quickly capture images of whatever you have on your screen, and paste it into the PowerPoint presentation (using “Paste special”). In which case you are actually creating large TIFF images in your presentation (at least for PowerPoint 2016).

Even though the images in the presentation are compressed/zipped when saving the presentation file, the presentation will still be significantly larger than it actually needs to be.

However, once you realize that your presentation is 100+ MBs, you don’t have the time to re-save a lower-quality version of each image and then substitute that image in the presentation.

Q: What to do?

A: First,

use the built-in “Compress Pictures” feature: Go “File -> Compress pictures”, or select any image, go to the “Picture Tools” toolbar, and select the “Compress Pictures” icon (four arrows pointing to the corners of an image). This tool allows you to down-scale pictures and removed cropped-out areas, and can be applied to all pictures in the presentation at once, but does not change the image format of pictures in the presentation. Make sure to save your presentation under a new name, in case you realize you need to some of the original, uncompressed pictures!

A: Then,

if the presentation file size is still excessive, use pptx-downsizer!

pptx-downsizer will go over all images in your presentation (pptx), and down-size all images above a certain size.

  • By default, all images are converted to PNG format (except for JPEGs which remains in JPEG format). This is particularly relevant if you have a lot of TIFF files in your presentation, e.g. if you copy/paste images or use the Mac “screen capture” feature when adding images.

  • You can also choose to use JPEG format (recommended only after doing an initial downsizing using PNG).

  • If images are more than a certain limit (default 2048 pixels) in either dimension (width, height), they are down-scaled to a more reasonable size (you most likely do not need very high-resolution images in your presentation, since most projectors still have a relatively low resolution anyways.)

Q: How much can I expect pptx-downsizer to reduce my powerpoint presentations (pptx files)?

A: If you have copy/pasted a lot of screenshots (TIFF files), it is not uncommon to for the presentation to be reduced to less than half (and in some case one fourth) of the original file size. If you further convert remaining large/complex PNG images to JPEG, as a separate downsizing step, you should be able to get another 20-40 percent reduction. Of course, this all depends on how large and complex your original images are, and how much you are willing to compromise quality when compressing your images. You can use the --quality parameter to adjust quality of JPEG images.

How pptx-downsizer works:

  1. First it unzips the .pptx PowerPoint file to a temporary directory. Other ooxml files probably works as well, e.g. .docx Word files.

  2. Then, pptx-downsizer searches for image files with large file size. The file size is controlled with the fsize-filter parameter. It is possible to add additional file-selection filter criteria, e.g. set fname-filter="*.TIFF" to only convert TIFF image files, although this is typically not needed.

  3. pptx-downsizer will then go through all selected images and try to minimize them in the following ways:

    1. If the image dimensions are larger than img-max-size, pptx-downsizer will reduce the image dimensions (by an interger factor) so that the image is smaller than img-max-size.

    2. The image is then resaved in the selected format (default: jpeg) and quality (default: 90). pptx-downsizer can also be used to change image modes, e.g. convert transparent regions of PNG images to a solid color by setting --img-mode="rgb" --fill-color="#ffffff".

  4. Finally, the .pptx PowerPoint file is re-created and re-saved as Presentation.downsized.pptx.

Note: It is often useful to do multiple rounds of downsizing, e.g. first converting all large TIFF files to PNG format, then downsizing the downsized pptx to convert the biggest PNG images to JPEG (see “Examples” below).

Examples usage:

Make sure to save your presentation (and, preferably exit PowerPoint, and make a backup of your presentation just in case).

Let’s say you have your original, large presentation saved as Presentation.pptx

After installing pptx-downsizer, you can run the following from your terminal:

pptx-downsizer "Presentation.pptx"

If you want to change the file size limit used to determine what images are down-sized to 1 MB (≈ 1’000’000 bytes):

pptx-downsizer "Presentation.pptx" --fsize-filter 1e6

If you want to disable down-scaling of large high-resolution images, set img-max-size to 0:

pptx-downsizer "Presentation.pptx" --img-max-size 0

If you want to convert large images to JPEG format:

pptx-downsizer "Presentation.pptx" --convert-to jpeg

Advanced usage: Pause before re-creating the PowerPoint file. Let’s say you are a power user, and you need to do something very specific to some or all of the images in your presentation. For instance, adding watermarks before sending the presentation to someone else. If you pass --wait-before-zip to pptx-downsizer, the program will wait before it re-creates the presentation (but after downsizing the images).

Command line arguments:

You can always get a complete description of the program and the available command line arguments (parameters) by invoking:

pptx-downsizer --help

This should produce an output similar to the following:

$ pptx-downsizer --help
usage: pptx-downsizer [-h] [--fname-filter GLOB] [--fsize-filter SIZE]
                      [--convert-to IMAGE_FORMAT] [--img-max-size PIXELS]
                      [--img-mode MODE] [--fill-color COLOR]
                      [--quality [1-100]] [--optimize] [--no-optimize]
                      [--outputfn_fmt FORMAT-STRING] [--overwrite]
                      [--compress-type ZIP-TYPE] [--wait-before-zip]
                      [--on-error DO-WHAT] [--verbose [0-5]]

PowerPoint pptx downsizer. Reduce the file size of PowerPoint presentations by
re-compressing images within the pptx file.

positional arguments:
  filename              Path to the PowerPoint pptx file that you want to

optional arguments:
  -h, --help            show this help message and exit
  --fname-filter GLOB   Convert all images matching this filename pattern,
                        e.g. '*.TIFF' (default: None)
  --fsize-filter SIZE   Convert all images with a current file size exceeding
                        this limit, e.g. '1e6' for 1 MB. (default: 524288)
  --convert-to IMAGE_FORMAT
                        Convert images to this image format, e.g. `png` or
                        `jpeg`. (default: png)
  --img-max-size PIXELS
                        If images are larger than this size (width or height),
                        reduce/downscale the image size to make it less than
                        this size. (default: 2048)
  --img-mode MODE       Convert images to this image mode before saving them,
                        e.g. 'RGB' - advanced option. (default: None)
  --fill-color COLOR    If converting image mode (e.g. from RGBA to RGB), use
                        this color for transparent regions. (default: None)
  --quality [1-100]     Quality of converted images (only applies to jpeg
                        output). (default: 90)
  --optimize            Try to optimize the converted image output when
                        saving. Optimizing the output may produce better
                        images, but disabling it may make the conversion run
                        faster. Enabled by default. (default: True)
  --no-optimize         Disable optimization. (default: False)
  --outputfn_fmt FORMAT-STRING
                        How to format the downsized presentation pptx filename
                        Slightly advanced, uses python string formatting.
                        (default: {fnroot}.downsized.pptx)
  --overwrite           Whether to silently overwrite existing file if the
                        output filename already exists. (default: None)
  --compress-type ZIP-TYPE
                        Which zip compression type to use, e.g. ZIP_DEFLATED,
                        ZIP_BZIP2, or ZIP_LZMA. (default: ZIP_DEFLATED)
  --wait-before-zip     If this flag is specified, the program will wait after
                        converting all images before re-zipping the output
                        pptx file. You can use this to make manual changes to
                        the presentation - advanced option. (default: False)
  --on-error DO-WHAT    What to do if the program encounters any errors during
                        execution. `continue` will cause the program to
                        continue even if one or more images fails to be
                        converted. (default: raise)
  --verbose [0-5]       Increase or decrease the 'verbosity' of the program,
                        i.e. how much information it prints about the process.
                        (default: 2)


First, make sure you have Python 3+ installed. I recommend using the Anaconda Python distribution, which makes everything a lot easier.

With python installed, install pptx-downsizer using pip:

pip install pptx-downsizer

You can make sure pptx-downsizer is installed by calling it anywhere from the terminal / command prompt:


Note: You may want to install pptx-downsizer in a separate/non-default python environment. If you know what that means, you already know how to do that. If you do not know what that means, then don’t worry–you probably don’t need it after all.

Troubleshooting and bugs:

NOTE: pptx-downsizer is very early/beta software. I strongly recommend to (a) back up your presentation to a separate folder before running pptx-downsizer, and (b) work for as long as possible in the original presentation. That way, if pptx-downsizer doesn’t work, you can always go back to your original presentation, and you will not have lost any work.

Q: HELP! I ran the downsizer and now the presentation won’t open or PowerPoint gives errors when opening the pptx file!

A: Sorry that pptx-downsizer didn’t work for you. If you want, feel free to send me a copy of both the presentation and the downsized pptx file produced by this script, and I’ll try to figure out what the problem is. There are, unfortunately, a lot of things that could be wrong, and without the original presentation, I probably cannot diagnose the issue.

OBS: If PowerPoint gives you errors when opening the downsized file, please don’t bother trying to fix the downsized file yourself. You may run into unexpected errors later. Instead, just continue working with your original presentation.

Q: Why doesn’t pptx-downsizer work?

A: It works for me and all the .pptx files I’ve thrown at it. However, there are obviously going to be a lot of scenarios that I haven’t run into yet.

Q: Does pptx-downsizer overwrite the original presentation file?

A: No, by default pptx-downsizer will create a new file with “.downsized” added to the filename. If this output file already exists, pptx-downsizer will let you know, giving you a change to (manually) move/rename the existing file if you want to keep it. You can disable this prompt using the --overwrite argument.

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