In Digital Projection, are we missing the "black space"?

[Thom Steinhoff]

In traditional projection, the image is displayed for half the time, and the other half is dark. Thinking about it, it's really going at 48fps with an alternating black frame as the blades cover the frame and the film is advanced. I don't know enough about it to know that it is truly a 50/50 split between the frame shot and darkness--but maybe someone else can comment on this. let's just say for the sake of argument--it is.

However small, your brain fills in that "black space" by itself, and in my opinion--visually "invests" you in the movie at a different level. As a writer, I know that the more you invest the audience in connecting the dots for themselves--the more pleasurable it is for them--I think it's the same visually. Your brain does the "tweening" and gets pleasure from it. I think this is part of the reason why movies projected "feel" so much better.

To me, this is why something shot at 30fps or 60fps feels less engaging as there is less for you brain to do.

In 24fps, when you watch on television or digital projection--that "black frame" goes away and it just goes from picture to picture. The brain has less to do--other than focus on the stutter. I think this is why you perceive more stutter in a DVD than you do in a traditional theater--the image stays on the screen longer and then jumps immediately to the next one causing a stutter.

My question for the Cinematography experts is this: Visually, are we missing something without the darkness? Is it less engaging? Maybe these massive digital projectors in theaters actually have a shutter--I don't know. I only know my home theater projector doesn't.

Would we actually gain more pleasure from a digitally projected image--if the shutter is reintroduced?

 

[Dominic Jones]

I've thought for a long time that it would be interesting to build a digital projector with a built-in 2 or 3 blade shutter, and see whether it had a more pleasing effect to the eye than standard digital projection. Maybe when I upgrade to a 1080p projector my old 720p one will get a little mod!

FYI, film projectors usually use either a double or triple bladed shutter, so you essentially get 48 or 72 "frames" shown per second, but as the film is advanced only every 24th of a second, each frame is shown either 2 or 3 times - this reduces visible flickering, without changing the motion chracteristics of the format.

Cheers, and I'm glad someone else has had a similar thought - worst case scenario, we can both be wrong together!!

Dom.

 

[bobaandy]

If you where to reintroduce a black frame every other frame, I think you would find it much less then pleasurable and downright seizure-inducing.

 

[Dan Hudgins]

Flicker threshold...

Flicker threshold...

Would we actually gain more pleasure from a digitally projected image--if the shutter is reintroduced?

There is a subconscious link to seeing movement and attention, if someone throws a ball at you, your eyes will close before you realize what you see.

Since your eyes are keyed to pick up movement, and that is linked to the flicker threshold, and 24fps is near the flicker threshold, and since the shutter is needed to produce flicker, you may be on to something.

It is possable to build a projector, and has been done, that uses a rotating glass prism rather than a shutter, if watching movies with a prism projector made them less interesting then the flicker threshold linked to subconscious attention might have some validity?

 

[Thom Steinhoff]

If you where to reintroduce a black frame every other frame, I think you would find it much less then pleasurable and downright seizure-inducing.

Not thinking about it for home use, for that, I agree. But for the theater? Isn't that what traditiional projector's are doing?

Also, I'm not saying a "black frame" so to speak, I'm saying "a period between frames without light" likely with some kind of mechanical shutter.

 

[Charles Angus]

If you where to reintroduce a black frame every other frame, I think you would find it much less then pleasurable and downright seizure-inducing.

Why do you say that? That's how it works with film...

 

[Dominic Jones]

It is possable to build a projector, and has been done, that uses a rotating glass prism rather than a shutter, if watching movies with a prism projector made them less interesting then the flicker threshold linked to subconscious attention might have some validity?

You may have a point there Dan, but I would imagine, to be fair, that prism-based projectors did not catch on for other reasons - firstly, they are much more costly to produce, secondly they tend to introduce more distortion and thirdly they do still have a break between frames - just a shorter one and only one per frame.

It certainly seems to be the case that several equal gaps is better in viewing terms than one short gap with a long frame display time - hence why modern projectors use multiple-bladed shutters rather than a single bladed shutter with a wide angle.

The issue, to my mind, isn't necessarily whether a shutter-based digital projection is "better" in any quantifiable way, but simply that it might give more of that magical "cinema" feel.... But maybe not!

I doubt in either case if it's something that will catch on in the mainstream, but it might make for an interesting experiment and perhaps a rather unique home-cinema setup!!

 

[Joe G.]

"If you where to reintroduce a black frame every other frame, I think you would find it much less then pleasurable and downright seizure-inducing."

That's complete speculation. "Seizure-inducing" has to do with the rate of strobing. Obviously 24fps is shown, over a century of real world implementation, to NOT cause seizures.

 

[Dominic Jones]

With all due respect, there's no speculation involved at all - we know it's not a problem from experience. As Charles quite correctly states, it has been done for over 100 years in film projection. That said, watching 24fps footage with a single 180 degree shutter isn't all that pleasant for long periods of time, hence the introduction of two and three bladed shutters.

The question is not "can you put a mechanical shutter in a projector" - that is a given. The question is "would it be (artistically, not technically) preferable to put a mechanical shutter in a digital projector, where it's not technically necessary to have a shutter at all". An A/B test is the only way your going to be able to make that decision, and being a matter of artistic, rather than technical, preference, different people will have different opinions.

I think it would be interesting to do, and I suspect I might just like it!

 

[Dan Hudgins]

EEG or PET scan

EEG or PET scan

An A/B test is the only way your going to be able to make that decision, and being a matter of artistic, rather than technical, preference, different people will have different opinions.

I think it would be interesting to do, and I suspect I might just like it!

It might be possable to use an EEG or PET scan to see if parts of the brain in viewer related to attention are active more or less in people exposed to 48Hz images that are 50% black and moving. The eye-brain is keyed to notice changes in a time window that is slower than 60Hz and faster then 24Hz, so there may be a physical "twitch" type responce in the eye-brain to have the stimulation come and go at 48Hz.

Stroboscopes are sometimes hooked up to EEG machines to blink at certian Hz to cause changes in EEG traces, so it is known that blinking lights have a different affect on the brain than constant lights.

If a video projector is a constant light it would then have a different affect on the eye-brain than a blinking movie projector.

The movie projector's 48Hz may be like a visual vibrator for the eye-brain?

Maybe theatre attendence is lower in theatres that use three blade rather than two blade projectors? The brightness of the projector also changes the flicker threshold, so you need to measure the brightness and if it is 2 or 3 blade and cross reference to attendence on a plot to see if there is a correlation for a "visual vibrator" effect?

Eye strain in 3D stereoscopic film moves may be due in part to lack of sync between the flashes of the right and left projectors, so the brain gets a criss-cross stimulation rather than both eyes on and off at the same time.

 

[Steven Caesare]

There are some projectors that are doing "Dark Frame Insertion" now. Many have it as part of their "cinema effect" setting.

Sony's VPL-VW200 and VPL-VW80 are a couple such units, although it seems to be billed more as a contrast-enhancing feature.

See: http://www.sony.lv/biz/view/ShowCon...0893359&sectiontype=Home&preserveContext=true

-Steve

 

[David Rasberry]

Video projectors are not constant. They present a series of still frames just like film. Between each frame is a blanking interval where the image is dark. This blanking interval is not full frame height though. If you could see it, it would be a black bar rolling thru the image from top to bottom. This does show up when an electronic display is filmed by a camera without a synchronized shutter. The mechanical frame change in a movie projector has to be completely covered by dark shutter to avoid vertical smearing of the image.

 

[ericyoung]

In traditional projection, the image is displayed for half the time, and the other half is dark. Thinking about it, it's really going at 48fps with an alternating black frame as the blades cover the frame and the film is advanced. I don't know enough about it to know that it is truly a 50/50 split between the frame shot and darkness--but maybe someone else can comment on this. let's just say for the sake of argument--it is.

However small, your brain fills in that "black space" by itself, and in my opinion--visually "invests" you in the movie at a different level. As a writer, I know that the more you invest the audience in connecting the dots for themselves--the more pleasurable it is for them--I think it's the same visually. Your brain does the "tweening" and gets pleasure from it. I think this is part of the reason why movies projected "feel" so much better.

To me, this is why something shot at 30fps or 60fps feels less engaging as there is less for you brain to do...Visually, are we missing something without the darkness? Is it less engaging? Maybe these massive digital projectors in theaters actually have a shutter--I don't know. I only know my home theater projector doesn't.

Would we actually gain more pleasure from a digitally projected image--if the shutter is reintroduced?

I've thought for a long time that it would be interesting to build a digital projector with a built-in 2 or 3 blade shutter, and see whether it had a more pleasing effect to the eye than standard digital projection...film projectors usually use either a double or triple bladed shutter, so you essentially get 48 or 72 "frames" shown per second, but as the film is advanced only every 24th of a second, each frame is shown either 2 or 3 times - this reduces visible flickering, without changing the motion chracteristics of the format.
...Dom.

Interesting ideas - I wonder if a multi-bladed shutter combined with a higher "native" frame rate than 24fps might be the best of both worlds. The smoother motion rendition of video without the video "live TV" feel.

I'm with James Cameron in that I hate the smear of a pan, or the stutter of an object crossing frame in film, but I dislike the documentary feel of video when watching a narrative feature film.

 

[Dominic Jones]

Video projectors are not constant. They present a series of still frames just like film. Between each frame is a blanking interval where the image is dark. This blanking interval is not full frame height though. If you could see it, it would be a black bar rolling thru the image from top to bottom. This does show up when an electronic display is filmed by a camera without a synchronized shutter. The mechanical frame change in a movie projector has to be completely covered by dark shutter to avoid vertical smearing of the image.

True of CRT (and to a certain but slightly different degree DLP) projectors, but not true (or at least not to any major degree) of LCD projectors (or any LCD based display) - similarly, you do not need a "clearscan"-style capability to shoot LCD displays (or plasma, for that matter, although of course there are no plasma projectors!).

Even for those projectors that have a blanking cycle, it may be beneficial (again, I'm back into artistic rather than technical territory here) to have a shutter swipe transition hide the blanking cycle (as one of 2 or 3 such cycles), much in the same way as mechanical shutters can be implemented in digital cameras to hide rolling resets... All fun stuff!

Steven - that's interesting, thanks for the info. I wonder how the motion characteristic of the "blanking frame" compares to a shutter swipe - is it a global or rolling blank, for instance? Any idea?? I'd be interested to see one in action for myself - maybe it's time for a cheeky "I'm not actually buying anything but can I demo some kit" visit to the local Home Cinema store!...

Cheers again for a good chat all!
Dom.

 

[Michael Lindsay]

slightly OT but may interest..

I believe Barco's new grade 1 LED production monitor uses a black frame insertion technique.

I'm hoping its a good one as Sony's 15k LCD is disappointing

 

[Steven Caesare]

Steven - that's interesting, thanks for the info. I wonder how the motion characteristic of the "blanking frame" compares to a shutter swipe - is it a global or rolling blank, for instance? Any idea?? I'd be interested to see one in action for myself - maybe it's time for a cheeky "I'm not actually buying anything but can I demo some kit" visit to the local Home Cinema store!...

Cheers again for a good chat all!
Dom.

Most of the projectors capable of displaying true 24p content do so at some even multiple of 24... such as actually displaying at 96 or 120 Hz (in order to meet the minimum panel refresh requirements). Because of the sample-and-hold nature of the panels, there is no inherent flicker.

I think that the Dark Frame techniques may alternate every other frame (at say 96Hz) as a dark one. As such, the "flicker rate" would be 48Hz... which like film projectors, is above our threshold for detecting.

I'd also assume that because the dark frames aren't really black, but simply darkened content frames to enhance apparent contrast, that the overall effect may be less "flickery" than a full black frame would otherwise be.

It does have the effect of reducing the overall lumen output of the projector, however.

-Steve