OMG......ASUS, this thread just saved you a return. So glad I found it, I've been reading up on this for a few days and this was burried in search results pointing to a lot of stuff that didn't work. I was really disappointed and ready to return my monitor. I was gaslighting and trying to convince myself it was a windows HDR issue or the content was just poorly mastered, or I didn't know how to properly calibrate. I purchased my monitor and immediately did the FW update to V29 so I never really got to see it with what it shipped with.
This is absolutely a firmware issue, and downgrading to V28 after doing nothing else fixed everything. I had tried everything I could on V29, using different color profiles, using the MS HDR calibration app, tweaking nvidia individual color settings, tried reshaders, even tried creating my own backgrounds to try to fix the horrible grey to black stepping and color banding thinking it was just bad content. To make it even look remotely passable I had to change brightness/contrast/gamma for different content. I could never get it to calibrate quite right across the board on all colors at the same time, soI had to choose hiding the banding or having certain colors washed out.
It seems pretty obvious that with V29 the monitor was not handling HDR colors and gradients properly. Windows UI looked irradiated, colors were all off and I have a 32" LCD with HDR right next to it to compare. I had to do a lot of tweaking to get individual colors looking remotely close but it always messed with the greys and blacks too. Anything with a light glow on top of a pure black looked like a blocky blotched mess. Dark scenes in movies looked like nuclear waste, just melted hard bands of black or grey with splotches of color, etc. I was too disgusted and embarrassed by it to take a picture before trying the downgrade, never even occurred to me that was the issue. V28 doesn't look as vibrant, but I'll take this any day. Will see if I can dial it in.
Thank you OP for post, and others for chiming in about the downgrade. Long time and happy Asus user, a little shocked "choose a different firmware that suits you" is a recommendation. There was no way the image I was getting out of v29 would have been acceptable to ANYBODY. Details if it helps:
PG48UQ
GTX 4090 - w/ gsync windowed & fullscreen mode; tried 60,120, and 138hz
DP (using the cable it came with)
