Would you like to inform if this option informed below in the site would already be available to be enabled directly within the retroarch? Because the publication on the site is from January 2016 ... may be that there is already another way to enable the mentioned resource! (i'm not good at linux....)
"Smoothing the Video Output with Bilinear Filtering
The in-game screen grabs included in this post all feature a degree of smoothing, which is applied by via Libretro to the emulator in the form of bilinear filtering. I choose to apply this mainly to combat the extremely apparent dithering effect which a great many PlayStation games utilise.
The dithering effect works well on the original PlayStation hardware, when connected to a cathode ray tube (CRT) television via RF or composite cables; in this case inherent limitations in the technology are exploited to cause a natural anti-aliasing effect to blend the dithering, creating the illusion of more, and smoother, colours. Unfortunately on modern LCD displays the effect becomes revealed for what it truly is – a rather obvious pixelated grid.
Whilst switching the bilinear filtering on or off would seem an obvious feature to be made available via the RetroArch/Libretro menu, I have not located an entry which does so. Instead I added an entry (video_smooth = true) to the PlayStation emulator’s configuration file to achieve this:
Locate and edit the retroarch configuration file for the PlayStation emulator:
Sudo nano retroarch.cfg
Add the entry to enable video smoothing:
All settings made here will override the global settings for the current core
rewind_enable = false
added next line
video_smooth = true
Save the changes – this applies bilinear filtering to every game played on the PlayStation emulator from now on."