How to get more pixels when you export Powerpoint slides to graphic files
Microsoft, in their wisdom, cripple PowerPoint’s abilities to export slides to high resolution graphic files, and by default they compress images imported to a mere 220 pixels per inch or less. Here are a couple of tricks to improve things.
Caveat: if you insert low resolution images into PowerPoint, you cannot increase the usable resolution by exporting to a higher resolution. You just get large pixelated files. If you insert high res files but let Powerpoint “compress” the images, you will reduce the resolution of the images and will lose detail that you cannot recover (see 1 below).
1. Tell PowerPoint not to automatically compress imported images.
Open PowerPoint.On the File menu choose Options. In the options dialog choose Advanced. In the right panel under Image Size and Quality select Do not compress images in file.
This setting will stay with the file, but you will need to reapply it for new files where you want the highest resolution in your images. There is probably a way to make this the default… stay tuned.
Also, don’t use the “compress pictures” functionality unless you are happy with reduced resolution/quality of your images.
2. Change the export resolution for PowerPoint slides
This step involves editing the registry. The registry is a database maintained by the system of all the relevant settings that allow programs to work. If you muck up the registry, things might not work afterwards. If you are unsure, get expert assistance. That said, it isn’t difficult if you follow the instructions here: https://support.microsoft.com/en-us/help/827745/how-to-change-the-export-resolution-of-a-powerpoint-slide [UPDATE 2018-04-17: this URL no longer works. Try https://answers.microsoft.com/en-us/office/forum/office_2013_release-powerpoint/how-to-change-the-powerpoint-export-resolution-of/786f5a11-2c31-4234-95a3-d28943fa2987 or look up how to edit the registry (a quick look on google should do it, or ask your local friendly windows guru). Locate HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\PowerPoint\Options. Add or edit DWORD Value ExportBitmapResolution. Set this to the desired resolution. Note that whatever resolution is set in registry, older versions of Powerpoint will not export files with more than 3072 pixels on the longest side. On my new installation of office 365 they seem to have fixed this bug so it exports at the specified resolution.
Since this change is done in the registry, it will be in operation whenever you use PowerPoint from then on. Note that if you upgrade to a new powerpoint, the registry change may not be copied to the new version (It seems to have carried through with my recent upgrade to office 365) so you may need to repeat the process after each version upgrade.
Note that no matter how high you set the resolution in the registry PowerPoint will not export slides as image files with sides greater than 3072 pixels – that is usually enough, but may not be for some applications [UPDATE 2018-04-17: note that the current office365 has fixed this – see above]. The next section has an approach that gets around this limitation.
3. Alternative — export by printing to a PDF file
This is less convenient but does not need changes in the registry. Print the slide (or slides) using a PDF writer. WIth Adobe’s PDF writer you can set a high resolution (the default is to compress large images to 150 ppi). In the print dialog with Adobe PDF selected choose Properties
In the Document properties dialog, choose a setting with high dpi settings such as Press quality:
Or you can edit one of the other settings and change the images compression properties to whatever resolution you want.
If you don’t have adobe PDF writer, there are lots of alternative free programs such as Foxit PDF, Bulllzip PDF or CutePDF Writer which can give high quality PDF output, allowing you to configure the graphics resolution settings to your needs.
Once you have the slide(s) saved as a PDF file containing embedded high resolution images you can save them as image files from Acrobat (paid version) or open them using programs such as (expensive) Adobe photoshop or Adobe Illustrator, or (free, open source programs) GIMP (sim to photoshop) or Inkscape (sim to Illustrator), from where you can export to whatever graphic file format you require.