So sizes aside – the best size for a Facebook image is varied on context and varies greatly over time (at time of writing I recommend a 504w x 403h image) but that’s not what this post is for.
There’s a great guide to Facebook page image sizing as of 21/05/14 here
I’m more concerned with output, as I often will be putting out images with large bold text on flat colours, which are of course the first thing that gets destroyed by Facebook’s compression algorithm as it uploads.
Now, previously I would just output as an uncompressed .png. However some time around April of this year I noticed that the uncompressed pngs were being shrunk down and exhibiting ugly artefacts as below.
These pictures were uploaded as uncompressed pngs then downloaded again. In particular note the noise around small areas of flat colour.
So I was a little perturbed about how to get that nice crisp colour back. Turns out it was simple though: just use the default compression that comes up when saving as a .png
Here’s the same images after outputting as compressed .png and uploading to Facebook.
Makes a world of difference, right?