1920x1080 HiDPI on older iMacs

[Bacci]

My setup is a mid 2010 27" iMac (11,3) with a Philips 288p 28" 4K external monitor, running OS X 10.10.2 at the moment of this typing.
Managed to get 1920x1080 working in HiDPI on the Philips (based on 3840x1440@30Hz) which looks awesome. The old iMac can run its own screen at 2560x1440@60Hz at the same time.

I'm looking for a way to match screen scaling however, which would be easier to work with in extended desktop mode.

The options are:
- to just run the iMac's monitor in 1920x1080 but that looks too blurry.
- to run the iMac in 1920x1080 in HiDPI based on its native resolution
- to scale the Philips to 2560x1440 based on 3840x2160@30Hz.

Up until OS X 10.9 it was possible to create a scaled resolution in SwitchResX higher than the monitor's capabilities, which would result in seeing a HiDPI mode at 1/2 of that resolution.
Running 10.10 the OS rejects any scaled resolutions exceeding the monitor's capabilities (at least for my graphics card, the AMD HD5750), which rules out the latter 2 options.

Has anyone so far found a new way to create custom HiDPI resolutions in Yosemite?

 

[R2FX]

My setup is a mid 2010 27" iMac (11,3) with a Philips 288p 28" 4K external monitor, running OS X 10.10.2 at the moment of this typing.
Managed to get 1920x1080 working in HiDPI on the Philips (based on 3840x1440@30Hz) which looks awesome. The old iMac can run its own screen at 2560x1440@60Hz at the same time.

I'm looking for a way to match screen scaling however, which would be easier to work with in extended desktop mode.

The options are:
- to just run the iMac's monitor in 1920x1080 but that looks too blurry.
- to run the iMac in 1920x1080 in HiDPI based on its native resolution
- to scale the Philips to 2560x1440 based on 3840x2160@30Hz.

Up until OS X 10.9 it was possible to create a scaled resolution in SwitchResX higher than the monitor's capabilities, which would result in seeing a HiDPI mode at 1/2 of that resolution.
Running 10.10 the OS rejects any scaled resolutions exceeding the monitor's capabilities (at least for my graphics card, the AMD HD5750), which rules out the latter 2 options.

Has anyone so far found a new way to create custom HiDPI resolutions in Yosemite?

have you enabled HiDPI mode in Terminal? I did try it on my unibody MBP 15" and it worked in a same way as in 10.9

 

[Bacci]

have you enabled HiDPI mode in Terminal? I did try it on my unibody MBP 15" and it worked in a same way as in 10.9

I did. The highest available HiDPI res for the iMac display is 1280x720, can't seem to find a way to run the iMac scaled to 1920x1080 but based on its native resolution (2560x1440).