Blur Busters Open Source Display Initiative – Refresh Cycle Shaders
blurbusters.com
blurbusters.com
Can you use this method just to reduce blur without reducing brightness, on any game? They mention reducing blur for many things other than retro games in "Possible Use Cases of Refresh Cycle Shaders" but does reducing blur in a flight simulator also make it visually look like a CRT with phosphors?
Don't visual effects people go to lots of effort to add motion blur? Why would you want to remove it?
Why are they trying to simulate old CRT displays?
Can someone explain what this is about?
Most good monitor reviews of high Hz displays (eg: 120Hz+) take fast photographs of moving objects (typically from Blur Busters' 'Test UFO' web page) to demonstrate how good or poorly a monitor handles fast moving content.
One technique of significantly improving motion clarity is inserting frames of pure black in the display output (aka BFI, black frame insertion). A downside is some are sensitive to this where it causes eyestrain.
This CRT beam simulating shader is said to be similarly effective to BFI at improving motion clarity but with the benefit of reducing eyestrain. However from what I understand the current version is limited to simulating a lower Hz display and requires a higher Hz monitor.
All this is distinct from the kind of in-media motion blur that can be enabled in games or seen in recorded video. It's instead about the monitor not being able to render fast moving content clearly enough which leads to non-crisp output frames.
Whereas what Blur Busters (and similar enthusiasts) are focused on is how accurately frames are (perceptibly) displayed on the screen, so ideally each input frame is perfectly presented without any interference from prior frames (due to limits of panels in keeping up with changing the pixels from one frame to another, very rapidly, causing blurring).
The ultimate goal, in a perfect scenario, is for input from say a video game running at 60 frames per second to have each frame perfectly rendered like individual screenshot stills, one after the other. In reality for most monitors displaying such content there's not enough distinct separation between frames, leading fast changing pixel content (like objects moving) to blend into each other, causing blurring at the monitor level.
The BFI technique, by inserting alternating black frames in the output, mitigates the inter-frame blending issues since instead of the prior frame being various colors (ie: of the prior input frame) it's starting from pure black which dramatically reduces frame blending artifacts and perceptibly makes the motion clarity more distinct.
In a CRT the “pixels” start to fade immediately leaving the full screen mostly dark as the beam sweeps over the screen. It never shows a full frame.
One could say that modern screens are more like slide shows, while BFI tries to make them more like stroboscopes.
The blurring effect is more pronounced ate low refresh rates, its just that BFI requires at least 120hz to male sense at all.
(see this youtube video showing one in slow-motion to get an idea: https://www.youtube.com/watch?v=3BJU2drrtCM)
The "soap opera feel" is precisely the goal of motion interpolation on 24 fps source. It reminds people of soap operas because they were often broadcast 60i instead of 24p. The weird part is that many people somehow prefer the terrible 24 fps to higher film frame rates.
But it's also that a DP / cinematographer on a movie is crafting shots in ways that knowingly make use of a 24 fps framerate. There are consciously chosen effects that are in the shot, particularly directional motion blur that acts as a visual cue (like in action sequences or with hand-held cameras), which gets destroyed when the frame rate is increased without adding additional blur in the right places in post. Rather than a smoothly increasing/decreasing blur that creates a sort of ease-in-out as the camera or subject changes speed, you end up with jagged, rapid shifts in direction and speed which make well-crafted motion sequences feel either jarring or as if they're not really moving. I suspect that if a director were shooting originally at 60 fps they would have probably made the necessary adjustments in post production to achieve the effects they wanted, which they initially got by tuning their shots to 24 fps. But when it's done automatically by some software in a TV set, all of that subtlety is lost.
It's sort of like if you took an oil painting and say the colors look more lifelike in digital reproduction: That may be true, but it wasn't the artist's intent. The artist understood they were working with a particular palette and worked within its limitations to achieve their desired effects.
My contention is that it's not the higher frame rate which bothers people, per se, but that all the motion blur (slight as well as heavy) in a well-shot 24 fps movie is intentional, and therefore the problem is that removing it detracts from the intended effect of the shot. If you chose to replicate the original blur across 60 fps, rather than interpolate the sharpest possible interstitial frames, people might not have the same negative reaction.
Motion blur made a bit more sense on the 30fps Xbox 360 and PS3 games.
This is because our retina has a very low "refresh rate", which means things can easily blur together. Smooth pursuit prevents that. However, modern sample-and-hold displays like LCD and OLED work against Smooth pursuit. If you watch anything moving on a screen (including "still" objects moving on screen due to camera movement), your eye will automatically track those objects if they are momentarily the focus of attention, which should make them be still relative to your eyes and thus appear sharp.
However, since the tracked object is being still relative to your eyes and the individual frames on screen are being still relative to your screen, the frames move (are not being still) relative to your eyes. Which means they appear blurry during smooth pursuit, when in reality they should be perfectly sharp.
For example, your eyes track a sign that moves on the screen due to camera movement. Say it moves 10 pixels per frame horizontally. This means you will see a 10 pixel wide horizontal blur on this sign. Which could make it unreadable. In reality (without screen with a real sign) the sign would appear perfectly clear.
On CRT screens this doesn't happen (to the same extent) because the frame is not displayed for the entire frame time (e.g. 1/60th of a second) but much shorter. The CRT just very quickly flashes the frames and is dark in between. Strobing/flickering basically. So if the tracked object moves 10 pixels per frame, the frame might only be (say) visible for 1/5th of that frame time, which means it moves only 2 pixel while the frame is actually on screen. So you get only 2 pixel blur, which is much less.
Of course at 60 FPS you might instead get some degree of perceptible flicker (computer CRTs therefore often ran higher than 60) and in general the overall achievable screen brightness will be darker, since the screen is black most of each frame time. CRTs had a low maximum brightness. But they had very little of the "persistence blur" which plagues sample-and-hold screens like OLED and LCD.
The motion blur intentionally introduced by video games is there to make moving objects appear smoother that are not tracked by our eyes. In that case motion blur is natural (since smooth pursuit doesn't try to remove it). So some forms of motion blur are undesirable and others are desirable.
The optimal solution would be to run games (and videos content in general) at an extremely high frame rate (like 1000 FPS) which would introduce natural perceptible motion blur where it naturally occurs and remove it where it doesn't naturally occur (during smooth pursuit). But obviously that would be computationally an extremely inefficient way to render games.
By the way, if you have a screen with 120+ Hz you can test the above via this black frame insertion demo, which emulates how CRTs work:
https://testufo.com/blackframes
On my 120 Hz OLED screen, the 40 FPS (1 frame + 2 black frames) UFO looks as clear as the native 120 Hz UFO. A real 60 or even 80 Hz CRT screen would be even better in terms of motion clarity. Perhaps better than a 240 or even 480 Hz OLED.
There really is no need for an expensive RetroTink if we had this. Some manufacturer must be able to do it and the rest would follow.
The technique is for when you have X fps content and Y fps capable monitor, where Y > X. In games, you'll still render at your old FPS cap, but this shader is for relatively cheaply generating extra frames that will make the content look smoother / sharper.
From Gemini: "Display inversion is the process of alternating the voltage between positive and negative for each pixel on an LCD screen to prevent damage. This process is called polarity inversion."
If display manufacturers knocked that on the head for certain scenarios then surely we could just have a simple block of horizontal screen scrolling down the display at high refresh rates?
Phosphor fall off as far as can be seen in Slo Mo Guys is quite a small effect not on the scale of this shader.