iMac 27" 2K Late 2013 - images are distorted in non-native res

[venique]

I have an iMac 27" Late 2013 with 2K display whose native resolution is 2560x1440 and 755M 1GB.

Due my visual acuity I'm using it with scaled resolution - 2048x1152. In natively supported versions of macOS (like Sierra, High Sierra, Catalina) it works like a charm in terms of image quality and fonts sharpness (if you don't compare it to Retina displays).

But with newer versions of macOS like Big Sur, Ventura or Sonoma that I've successfully tried just in few clicks via OCLP I've got fuzzy, blurry and distorted images. Mostly it noticeable at small colorful icons. For example (sorry for photos, it's very hard to catch it on camera):



And how clear it looks in native resolution:



It's impossible to show you these artifacts on screenshots because there is no any visible issues on them at all. So it seems that some render to LCD problem is have place.

I've tried to switch between resolutions (even custom) and discover the following:

• 2560x1600 - good
• 2560x1440 - good
• 2048x1152 - issue
• 1900x1200 - issue
• 1920x1080 - issue
• 1600x1200 - good
• 1680x1050 - good
• 1600x900 - good

So, obviously, I can use native resolution which too small or 1600x900 which is too large. Any others are have artifacts or just are not 16:9 aspect ration.

I've spent nights with RDM, BetterDisplay, SwitchResX, EasyDisplay and whole bunch of scripts to play with resolution, font smoothens, OCLP patches and even trying to switch display into RGB 4:4:4 mode. Of course, this problem is not getting solved by rebooting, reinstalling macOS etc. Finally, I decided to replace LCD and still have no luck. It was silly because at older macOS everything works fine so it's not a hardware issue but I wanted to replace it anyway so whatever...

I already asked about this problem at Ventura thread and OCLP Discord but nobody helped me. That is really exhausted me and I don't know how to fix this strange issue. May be you guys have some thoughts about it? Thanks in advance anyway!

 

[venique]

For all who struggle like me with poor (I would even say 'defected') image quality at 2K iMac's with after-Catalina macOS: use one-key-hidpi patch (can be googled at github).

I downloaded it, selected 'Enable HiDPI', choosen native '2560x1440' resolution and after reboot selected 1920x1080 resolution in macOS settings. It increased UI scale to comfort size and most important - resolved problem with bad image quality. Now every icon and image are clear and have better quiality even more than in native 2k resolution without HiDPI. What about fonts... I never thought that they could be so smooth at non-Retina display.

After so many days and false tries it finally solved with most non-obvious way.