Comment by Springtime | Hacker News Reader

Comment by Springtime | Hacker News Reader

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This is about improving motion clarity, so each displayed frame of moving content looks crisp rather than having blur (something that monitors can struggle with even at high refresh rates / high Hz).

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.

Thank you, that's a really great explanation.

What is the method used on newer TVs that attempts to double the framerate / interpolate frames / make everything shot on film look like an overlit soap opera? I find it impossible to watch; it destroys the lighting and the performances. My recollection of CRT TVs was that they had a lot of blur, both motion and spatial, and that was kind of what made them feel warmer and more analog / less overly crispy.

That's typically called 'motion smoothing' and yeah that's trying to interpolate frames to manipulate lower framerate video (like 24FPS) into higher framerates in an attempt to make scenes like panning shots 'smoother' at the expense of a soap opera feel and interpolation artifacting.

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.

It’s not that the frames blend in the screen. Screens are perfectly capable of switching the pixels fast enough. It’s rather that each frame is displayed for to long.

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.

CRTs don't darken that fast, one way to observe this is that CRTs don't appear black in photos/video with shutter times << 1/60

They do darken that fast (not fast enough you can't catch it in a high speed camera, but much faster than a frame). Most of the apparent persistence in the CRT comes from the retina/camera exposure, not the phosphor. A CRT has a sharp peak of light that quickly falls off, but the peak is bright enough that even though it is brief, when averaged out in an exposure in the camera it still appears bright enough to form an image.

You've never taken photos of a CRT, have you? Even at like 400 ISO equivalent, only about a third of the screen is illuminated.

They frequently flicker or are only showing part of an image in video footage or photos, for exactly this reason. They're a right headache to film clearly.

(see this youtube video showing one in slow-motion to get an idea: https://www.youtube.com/watch?v=3BJU2drrtCM)

Thanks for the link. It seems i'd concluded this a bit wrong from seeing those half lit frames (like at 1:35 of this YT video).

Yes, the relevant blur here is in your retina, as it tracks a moving screen object, called "sample and hold" blur. 60 fps is not enough when the pixel persists for the full frame duration -- the pixels smear across your retina.

>at the expense of a soap opera feel

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.

I think you're right that it's partly a subconscious association with what we're used to seeing at higher frame rates (TV and video games).

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.

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