A handy guide for when to save images as JPEGs, PNGs or GIFs

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Thanks to David Green for flagging up this whoishostingthis.com infographic on Twitter - I found it useful because I tend to use a mixture of JPEG and PNG with saving images, with not much understanding of why I'm choosing what I'm choosing...

JPEGs reduce the size of an image by compressing it - making the image less detailed and so the file-size smaller, but effectively doing so in a way which the human notices least. This is important for web-use as everything each viewer of your website has to download - which is to say, have appear on their screen, rather than save to their computer - takes up bandwidth, and bandwidth costs money. One of the reasons I switched over to Squarespace from Wordpress.org is the unlimited bandwidth meaning I don't have to worry about upgrading my package to accommodate more.

PNG files can be transparent - they don't have to have a white (or black, or any other colour) background. This is truly useful because they can 'sit' on top of any background - so for organisatinal logos for example, it's essential to be able to drop them in over any kind of poster or slides or publicity materials, without an ugly white background delineating the logo from the rest of the content. PNG files generally take up more space than JPEGs but keep their quality better by not compressing the file in a lossy way. This is useful for something like uploading an image to Twitter; Twitter compresses the image, so an already compressed image can start to look really quite rough by the time it a Twitter user sees it.

GIFs I use a lot but never really have cause to make. They generally take up the least space and work better for created graphics rather than photographs.

After the recent posts on which format to choose when saving presentations, and which sizes to use when saving social media images, it seems only right to complete the set with one on how to save pictures too! So courtesy of whoishostingthis.com, here we are:

A file-format decision tree for saving PowerPoint presentations

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So which file format is best for saving your slides? It depends on the situation, but it's almost never the default .pptx you're offered. I made a little graphic below to act as a decision tree for choosing how to save your PowerPoint - click on it to be taken to a larger CC-BY-SA version on Flickr.

What it comes down to is this. Saving your slides as a .ppsx file - a PowerPoint Show - is usually the best option, because it opens the PPT up in Presentation View right away. This looks SO much more professional than the default .pptx PowerPoint file, which opens in edit view, revealing your notes if you have them, and the first few slides. Your audience seeing behind the curtain in this way isn't the end of the world, but why do anything to reduce the impact of the presentation you spent ages creating?

A .ppsx file will keep any animations you have in your slides (and embedded video and audio) and unlike a PDF it won't compress your images, so they'll remain high quality. 

However, sometimes you need to use a PDF - mainly when you've used non-standard fonts. PowerPoint claims to be able to embed fonts that aren't included in the Office Suite (but which you download yourself) so they'll work on other PCs - I've found this to be lies, lies, and more lies... It simply won't work - either for presenting on another PC, or for uploading to Slideshare. So saving as a PDF sorts this out - it retains your exciting font choices, and keeps things the right size and shape (you may have to go into the Save Options and untick the ISO box if your PDF doesn't behave itself the first time you save it - for example if Transparency effects aren't correctly rendered).

I also use PDF if the PC I'm presenting on has a different version of PowerPoint to the one I made the slides on - or if I don't know ahead of time whether it will. The version of PowerPoint shouldn't matter but it does, and the other day I had to subtly reformat a whole slide-deck after checking it on the latest version of Office and finding it had mucked around with the font-size for no good reason.

PDFs are the safe option. They work on pretty much ANYTHING. Lots of people never present with PDFs because it simply never occurs to them, but trust me it works fine! I do it 99% of the time because 99% of the time I use non-standard fonts - just click View then Fullscreen Mode and it works exactly like a PowerPoint in Presentation View (including using a clicker to move the slides along).

(There have been a couple of occasions where I've forgotten to do this, and turned up with a regular PowerPoint file to present on a machine with none of my special fonts installed. This has resulted in frantic downloading and rediting and saving in a panic, and is not recommended...)

NB: Never ONLY save your slides as PDF or PowerPoint Show - you need the .pptx file to actually come back and edit them later.

So next time you're saving your file, check if you really need to use .pptx, or whether another format is more appropriate.

You’ll find details of my Presentation Skills or PowerPoint workshops here: you can book an all-day or half-day session for your organisation, online or in person.