Today's 1.7 patch for the PS4 added the ability to save your screenshots and video via USB, which is definitely a lot more intuitive and comfortable than having to upload it to Facebook or Twitter, or even worse the convoluted method that required to send them to a secondary account to the PlayStation App on smartphones to get an uncompressed version.
Below you can see a comparison between screenshots saved with all four methods, which can be useful to know which one is best for the compression ratio you're looking for.
As usual, you should click on each screenshot to open a full resolution version, and you can compare them by flipping between different tabs in our browser. The Final Fantasy XIV screenshot has been taken in a dark environment on purpose. It's less beautiful but it lets you compare the quality of blacks.
Final Fantasy XIV: A Realm Reborn USB (504 kb)
Final Fantasy XIV: A Realm Reborn PlayStation App (1,203 kb)
Final Fantasy XIV: A Realm Reborn Facebook (402 kb)
Final Fantasy XIV: A Realm Reborn Twitter (228 kb)
inFAMOUS: Second Son USB (537 kb)
inFAMOUS: Second Son PlayStation App (1.369 kb)
inFAMOUS: Second Son Facebook (260 kb)
inFAMOUS: Second Son Twitter (274 kb)
Turns out that the file size for the pictures saved via USB is still about half than that of the same pictures sent via PlayStation App, indicating that the PS4 applies some compression to them before they're sent to your USB storage of choice. That's definitely quite surprising, considering that the ones sent to the PlayStation App have to travel through the net, so you'd think they'd compress them more. Apparently that's not the case.
Files uploaded to Facebook are even smaller (and a bit more compressed), while those sent to Twitter are the most compressed.
Quality-wise, it's really hard to notice a relevant difference between the USB, PlayStation App and Facebook methods, besides a very slight difference in definition and color gradient. Ultimately, if you want to go the extra mile for the lowest compression, the PlayStation App method still seems to be the way to go in most situations, but the USB method is much faster and easier, while keeping the quality very high. The fact that the difference is hardly noticeable means that the PS4 uses a very high quality compression method that has very little impact on the picture's details.
In addition to that, YouTube user Pablo_Klutch posted an interesting video comparison showing the difference between video uploaded to Facebook, saved via USB and grabbed via a capture card. You can check it out below.
//www.youtube.com/embed/mf222pX1hlo