A 4k screen would look superior than a downsampled 1080p image. Downsampling is awesome and cleans up the image a ton but textures still won't look as clear as they would on a 4k set.
Edit - This doesn't apply however to if a dev decided to add extra graphical features to a 1080p mode. I'm just strictly talking about IQ
A good anti-aliased image is more accurate to the ground truth. Than one without good AA. Thus image quality will look far better on the one with better AA.
At 4k, you will be getting IQ similar to the 1080p shot here in Titanfall, if not worse from the extra artifacts from CBR or whatever they decide to use.
Image quality isn't about the quantity of pixels. It's about the
quality of pixels. (And Titanfall here on standard PS4 based on the screenshots, is a soft smudgy mess.)
You might be able to see more pixels, but the underlying assets are still the same. And 1080p output with good AA will have a more accurate presentation because it's closer to the ground truth.
In today's world with as much complex shading and aliasing issues as there are. This will generally be the case.
When you can get AA and texture filtering at 4k output like this
http://u.cubeupload.com/MrBonk/f2affxiiiimg20150713224.jpg
(Days Gone gets pretty close because it uses UE4's TAA. But suffers some artifacts present from UE4's TAA and whatever solution they are using to get to 4k
http://images.pushsquare.com/news/2...s_insane_on_ps4_pro/attachment/2/original.jpg)
Then the IQ gap won't be as big. But as it stands, most PS4 games are going to be uprendered to 4k with CBR or similar solutions from a lower resolution. This comes with it's own artifacts that make aliasing slightly worse. And as far as AA goes once you get to 4k, they will be using basic PPAA, no AA or some form of TAA. (Then you get the issues that TAA creates. Using TAA with SSAA however, will mitigate some of them.)
Just some examples
4k screenshot of Horizon
http://static2.gamespot.com/uploads...onzerodawn_screens_septevent_3840x2160_05.jpg
Aliasing and CBR edge artifacts are very much an issue.
Downsample that to 1080p
http://u.cubeupload.com/MrBonk/3126133horizonzeroda.jpg
And most of the aliasing disappears.(Though much remains if you know what to look for)
Killing Floor 2
http://static4.gamespot.com/uploads/original/123/1239113/3144456-kf2_ps4pro_october2016+(3).png
http://static1.gamespot.com/uploads/original/123/1239113/3144452-kf2_ps4pro_october2016+(4).png
Very very rough looking.
Downsampled
http://u.cubeupload.com/MrBonk/3144456kf2ps4proocto.jpg
http://u.cubeupload.com/MrBonk/3144452kf2ps4proocto.jpg
Infamous
http://goingsony.com/system/file_up...iginal/04_-_Infamous_Second_Light_PS4_Pro.jpg
Fairly rough. Surfaces are blurry, aliasing of the normal variety, shader aliasing. And then artifacts on specular reflections and surfaces.
http://u.cubeupload.com/MrBonk/04InfamousSecondLigh.jpg
So....what will look better? 1080p down sampled on a 1080p TV or checkerboard 4k on a 4k TV?
See above.
Until games get better AA at 4k output (Which they will! Just look at Ratchet and Clank's update). A 1080p display with SSAA will look better.
Less aliasing=better image quality.
That's why bullshots look so good. And why screenshots people make of games on PC often look incredibly good. Image quality.