ScepticMatt
Member
In almost any console/PC comparison the issue of frame rate crops up, with people claiming they can't see the difference between 30 and 60 fps, or that even 120Hz isn't enough.
The truth is, they may all be right, at the same time.
So let's take some time and try to answer the question: What frame rate do you really need?
Considerations:
Motion perception
Critical flicker fusion
Input latency
Temporal aliasing
Motion perception (from 'slide show' to moving images)
Changing static images (as in motion picture) are perceived as in motion above 10-12 Hz. ('Phi phenomenon')
Images appearing in different locations (as in chase lightning) are perceived as moving in between them above 20 Hz. ('Beta movement')
So to sum up, you need at least 20 Hz to avoid 'slide shows'
Critical flicker fusion frame rate (Where motion becomes 'smooth' and CRTs 'flicker-free')
The reason for most of the confusion, because it depends a lot on the situation.
In simple terms:
* The brighter the game/screen, the higher the CFF
* The closer you sit, the higher the CFF
* The darker your room, the higher the CFF
* The more to the edge of the screen you look, the higher the CFF
* Motion blur hides CFF effects at the cost of detail.
This typically lies between 40 and 60 Hz on a HDTV. For PC screens and especially VR you may want a slightly higher rate.
Input latency (From 'laggy' to 'instant reaction on button press')
Inputs feel 'instant' as soon as total delay between button press and reaction on screen falls below 25ms.
So only looking at rendering latency, you'd need at least 40 Hz, but you'll want something higher to compensate for other sources of lag, if that remains possible.
25ms example: 120fps@120Hz Asus G-sync, 1000Hz mouse polling rate, Counterstrike: Go 128 tick server
(anandtech)
Temporal aliasing (stroboscopic/'wagon wheel' effect')
Due to the 'discrete' nature of the frame rate, you'll see multiple-images and wrong movement as soon as eye movement and screen movement differ.
Sadly, you would at least need 1000Hz to get to an acceptable level and without fast eye-tracking, would need too much motion blur to fix (think temporal FXAA).
Neither is feasible yet, but temporal upsampling (think TVs) could reduce averse effects in the meantime.
(blurbusters, example-keep eyes stationary: http://www.testufo.com/#test=photo&photo=eiffel.jpg&pps=960&pursuit=0&height=0)
TLDR: 20 Hz is necessary to avoid slide shows. What's necessary for 'smoothness' depends on a lot of factors, but 60Hz is enough in many situations.
Beyond the CFF frame rate there is no further improvement in smoothness, but higher frame rates may be preferable to reduce input lag and temporal aliasing until display technology advances far enough.
Annex 1: The latest model for CFF is:
more detailed information can be found at http://forums.blurbusters.com/viewtopic.php?f=7&t=333
The truth is, they may all be right, at the same time.
So let's take some time and try to answer the question: What frame rate do you really need?
Considerations:
Motion perception
Critical flicker fusion
Input latency
Temporal aliasing
Motion perception (from 'slide show' to moving images)
Changing static images (as in motion picture) are perceived as in motion above 10-12 Hz. ('Phi phenomenon')
Images appearing in different locations (as in chase lightning) are perceived as moving in between them above 20 Hz. ('Beta movement')
So to sum up, you need at least 20 Hz to avoid 'slide shows'
Critical flicker fusion frame rate (Where motion becomes 'smooth' and CRTs 'flicker-free')
The reason for most of the confusion, because it depends a lot on the situation.
In simple terms:
* The brighter the game/screen, the higher the CFF
* The closer you sit, the higher the CFF
* The darker your room, the higher the CFF
* The more to the edge of the screen you look, the higher the CFF
* Motion blur hides CFF effects at the cost of detail.
This typically lies between 40 and 60 Hz on a HDTV. For PC screens and especially VR you may want a slightly higher rate.
Input latency (From 'laggy' to 'instant reaction on button press')
Inputs feel 'instant' as soon as total delay between button press and reaction on screen falls below 25ms.
So only looking at rendering latency, you'd need at least 40 Hz, but you'll want something higher to compensate for other sources of lag, if that remains possible.
25ms example: 120fps@120Hz Asus G-sync, 1000Hz mouse polling rate, Counterstrike: Go 128 tick server
(anandtech)
Temporal aliasing (stroboscopic/'wagon wheel' effect')
Due to the 'discrete' nature of the frame rate, you'll see multiple-images and wrong movement as soon as eye movement and screen movement differ.
Sadly, you would at least need 1000Hz to get to an acceptable level and without fast eye-tracking, would need too much motion blur to fix (think temporal FXAA).
Neither is feasible yet, but temporal upsampling (think TVs) could reduce averse effects in the meantime.
(blurbusters, example-keep eyes stationary: http://www.testufo.com/#test=photo&photo=eiffel.jpg&pps=960&pursuit=0&height=0)
TLDR: 20 Hz is necessary to avoid slide shows. What's necessary for 'smoothness' depends on a lot of factors, but 60Hz is enough in many situations.
Beyond the CFF frame rate there is no further improvement in smoothness, but higher frame rates may be preferable to reduce input lag and temporal aliasing until display technology advances far enough.
Annex 1: The latest model for CFF is:
Code:
CFF = (0.24E + 10.5)(Log L+log p + 1.39 Log d - 0.0426E + 1.09) (Hz)
E = how far from center you look (degrees)
L = how bright (eye luminance, 215cd/m2 full white screen = 3.45 Log L)
d = field of view (degrees)
p = eye adaption (pupil area in mm2, typical 0.5-1.3 Log p)
