The PS4 is not going to be a True 4k console. And i think that is exactly what sony intended.
Make a console that has the power to do stable 1080p and extra power to dial up everything within that 1080p then output that in 4k with an upscaling alogarithm that has more power then the average upscaler has.
What you end up with is something that looks better than 1080p but bot as good as 4k, but a ge that has more IQ improvements outside just resolution.







