I recall back years ago having a good free PowerPoint compressor tool. It would shrink down file sizes, even convert .png embedded images to lesser file formats (i.e. gif at the cost of quality). Are there any good, free, preferably open source PowerPoint compressors that can be ran on a Windows platform? Also, if it doesn't require installation, and can be a standalone executable, that would be best.
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PPTX files are already compressed as part of the file format. Attempting to apply further compression to a PPTX file will be unsuccessful.
For PPT files your best bet is to downsample all of the images (i.e. don't have large bitmaps for backgrounds) and then put the PPT into a zip file for easy transfer. This doesn't require any additional software and work on all platforms.
Pictures are stored in PNG, JPG and sometimes GIF format, all compressed, it's true.
But a PNG or JPG from a 15 megapixel digital camera, while stored in compressed format, is way bigger than needed in PPT for most purposes. Some of the apps out there like the one I mentioned or another that I wrote, analyze the physical size of the image in PPT, determine how many image pixels are really needed, then downsample the image to match. So that 15megapixel image from the digicam might get resampled down to a 1024x768 or smaller JPG.
These apps can also use higher level JPG compression that PPT will use on its own.
AAMOF, you can do some of this stuff manually if you like. Rename the PPTX to give it a .ZIP extension, open the zip, locate and drag the images out to another folder or desktop, resample them down, apply more JPG compression, then drag them back into the original zip, save and rename back to PPTX.
You need to use Windows' native unzipping or 7Zip for this; Winzip seems to muck things up.