Why not a locked 45 FPS target?

[Ricki]

Hello,

Please could someone help me to understand why, it would appear to me, that only 30 or 60 frames per second are targeted in games?

Apologies if this is obvious to some of the better informed posters in the forum.

However, I’ve often wondered, mostly while reading digital foundry’s articles, why if developers are struggling to maintain 60 FPS in a game, at a desired resolution and image quality level, they do not try and target a locked 45 FPS?

I’m particularly interested in the above in relation to the Xbox One and PS4 where it appears the following combinations are mainly targeted?

· 1080p @ 60FPS
· 900p @ 60FPS
· 1080p @ 30FPS
· 720p @ 60FPS

Using COD Ghosts as an example on the Xbox One. As 1080p @ 60FPS was not achievable at the time, we ended up with 720p @ 60 FPS using, I understand, the same assets as the PS4 version.

Would it not have been an option to target 1080p @ 45 FPS? Instead of dropping all the way down to 720p?

(I’ve used COD and the XB1 to help illustrate my question but I’m interested in the answer in a wider context and not specific to anyone game or platform, if that makes sense)

Many thanks in advance.

 

[Graham]

Displays refresh once every 16ms, which means 60 times per second. This is where Vsync comes in (you want to sync what is rendered to the display refresh rate).

So at 60fps, you display one new rendered frame every time the screen refreshes, at 30fps you display a new frame on every 2nd display refresh.
The problem with 45fps, is that you'd have uneven display timing. Even frames would be displayed after one refresh, while odd frames would display after 2 refreshes.

So the time between frames being displayed on the monitor (not time to render) would be 16ms, 33ms, 16ms, 33ms, 16ms ..... Which would look like 'judder'.