I was fiddling with my monitor settings today (Dell U2415) and noticed the “Input Color Format” was set to “YPbPr” instead of “RGB”. This is a compressed colour space where the chroma channel has half the resolution of the luminance channel. Normally this would be used for TVs or video encoding rather than a PC monitor. That said I’ve been using it this way for two years without noticing…
The problem is Dell monitors advertise this mode along with RGB in their HDMI EDID. The driver for my AMD graphics card see this and prefers it over RGB with no way to override the selection. There is one creative solution I found which involves patching a local copy of the EDID and telling the driver to load that from disk rather than reading it from the monitor. I took the simpler option of spending a few quid on a DisplayPort cable which only supports RGB.
The result? Fonts look a bit sharper… maybe… but it’s hard to tell.