I haven’t seen anything official from Facebook about this but over the weekend I made a couple minor modifications to my personal and brand Timeline covers and noticed that after I uploaded them the quality of the images had improved dramatically, compared to the way they looked last week, which lead me to suspect that Facebook may have decreased the level of compression they’ve been using on those images. To keep file sizes small and page load times low, Facebook compresses the Timeline cover images quite a bit. When those images are purely photographic this usually still results in an acceptable quality photo but in the case of graphics or images with lots of red in them or text on them, the image quality is usually quite poor.
I know it’s not a very scientific approach but if you look at the before and after image below that shows a section of my own Timeline cover enlarged 200% to make it easier to see the difference, you’ll notice that the logo in the top image is not exactly crisp and there are a lot of “artifacts” (random pixels) around the logo, the text and the image with the woman on the right, whereas in the bottom shot there are hardly any noticeable artifacts and the image is clearly better.
To see the full effect of the dramatic difference, click the image to view at full size.
I’ve checked the file sizes of several Timeline cover photos and it appears that Facebook is using a jpg compression level of about 50% which is actually not too bad and which I also believe is considerably higher than they were using before.
If you have a Timeline cover photo that doesn’t look as good as you’d like, try reuploading it and see if you notice an improvement. I suggest saving any photos as jpg files with no compression and saving graphics (especially if they contain text) as png files. This way you’ll be uploading the highest quality image to start with.