Red and Lucasfilm?

[ericyoung]

...in the early days of cinema they tried out various different frame rates before deciding that 24fps was the most "natural" to the human eye. More recent research places the average human eye at an equivalent to 21fps, with 18fps as an agreed minimum, so the current frame rate seems perfectly sensible.

I think that the minimum frame rate was chosen as the minimum refresh rate at which the average person would perceive a series of still frames as portraying continuous motion. 24fps gives a sufficient margin above the minimum motion portrayal rate. But humans would still perceive flicker at 24fps. The projected rate is twice this, using a shutter, at 48Hz so that the majority of people would not perceive distracting flicker. Higher frame rates, while improving both motion and flicker, has a much higher cost in film stock, processing and printing, storage and transportation, more expensive projector and camera mechanisms, etc.

I'm no expert, but I'm guessing it's because the images are not in sync with the ones you see with your eyes (like you have to synch on-screen computer monitors with the camera when you are shooting to avoid strobing artifacts)

I believe your peripheral vision has much better motion sensing capabilities (ever look at a tube monitor thats 60hz or less, and see the flicker only in your peripheral vision?) ...

Our eyes don't have a universal sharply defined "framerate", so none of our filming frame rates will be "sync" with it.

Research does back up that our peripheral vision is better at motion sensing than our vision in the centre, and flicker is analogous to motion. Human flicker sensitivity threshold is somewhere around 48Hz, hence film being projected at 48Hz, and why 50Hz was adopted in the UK for TV refresh rates. Actually the US 60Hz would have been a better choice to have a greater margin away from our flicker sensitivity, but then there would have been problems with UK 50Hz mains interference causing very distracting moving patterns if UK TVs were 60Hz.

Another factor in peripheral flicker detection is that we don't normally watch screens out of the corners of our eyes, and our brains haven't adapted to filter it out. I've heard (but not confirmed) that many Americans coming to the UK initially find our 50Hz TVs very flickery in their central vision, being used to 60Hz, but quickly adapt so that they don't notice it

As Graeme says, our stereoscopic eyes and brain mounted in a mobile platform are a fantastic adaptive scanning system capable of integrating a picture in both time, 2d & 3D space, and frequency! And they are capable of adapting to and perceiving more than the hardware and economy limited systems of the past and present.

 

[Tom Lowe]

Lol at how these threads inevitably drift into super-minute technical details.... gotta love it.

 

[Craig Ryan]

You said it mate; notice how my post was quite relevant to the point of the thread, yet an entire new page preceeds it without any reference to it. But I can't blame anyone, we are just too intellectually trained to let a thread go by without indulging ourselves with the most interesting technical discussions

 

[Gavin Greenwalt]

Sorry to disagree here Graeme.

I think the microphone is what the lens is to a camera not the sensor.
The A/D converters are the sensor.
All that is before the A/D converters is analog, all that is after is digital.
All that is before the sensor is analog, all that is after is digital.
Think of a cook S4 as nice tube Neuman microphone.

It's still analog after the sensor. So the sensor as microphone is still a valid analogy since both output an analog signal.

 

[Graeme Nattress]

Both mic and sensor are a "transducer" - they convert input into electricity.

Graeme

 

[baro]

But humans would still perceive flicker at 24fps. The projected rate is twice this, using a shutter, at 48Hz so that the majority of people would not perceive distracting flicker.D

This is something I could not understand for a long time. How is it that when I look at a computer monitor that has a 50 Hz refresh rate I instantaneously start to get sick? But when I look at film projected at 48 Hz I do not get sick.

(With TVs you do not get sick as much because the phosphore remains bright for a longer time after a scan than how long it is bright on computer CRTs.)

 

[Graeme Nattress]

Flicker is also a factor of brightness level. Perhaps your CRT is too bright. It's also a cultural thing, where European's eyes have evolved to accept 50hz as corrrect, rather than 60hz. A computer monitor may not have high persistance phospors either, being really designed for a much higher scan rate than 50hz.

Graeme

 

[baro]

Brightness level is certainly important. A white screen is much more disturbing for me than a gray screen. But even in the case of a gray screen I can spot immediately a 60Hz computer display. I'm more sensitive to it than the average people. On several occasion I warned work colleges to set the refresh rate above 60 Hz. They did not understand what flicker I was talking about when I looked at their displays.

In my previous post I was looking for the right way to put it, but I could only remember it in Hungarian. Now I know, it is 'high persistance phospors'. Now that makes a big difference. My first IBM compatible computer was an XT with an I8088 processor. It had a monochrom Hercules display. I don't remember the refresh rate exactly, but it was not more than 60 Hz, probably 50 Hz. And the picture was rock solid. In comparison some VGA color displays displayed the 640x480 mode at 60 Hz and it was really flickery for me.

But when film is projected I think in regard of how long one frame stays on the screen in one flash can be considered the equvilent of low persistance phospor rather than high persistance phospor. Unless the projector changes the frames very rapidly so that the time the screen is dark is much shorter than the time the frame is visible on the screen.

This is why it is a mystery for me why I do not see flicker at movies.

 

[Dominic Jones]

Film projectors commonly use three blade shutters these days, which raises the effective flicker period to 72Hz, and also on these models the film is advanced slightly more quickly, to fit with the smaller shutter angle - so maybe you have been watching films in theaters equipped with these?

 

[Emmanuel Cambier]

Both mic and sensor are a "transducer" - they convert input into electricity.

Graeme

Sorry Graeme, my bad.

Yours Emmanuel

 

[Graeme Nattress]

Not bad, just different ways of looking things. There's no simple analogy to a lens in audio. Perhaps you could say that microphone placement or sound baffles could be analogous to a lens?

Graeme

 

[Emmanuel Cambier]

Well, the hardest part will be to find an audio analogy for RedOne I believe.
Congratulations to you guys.

Emmanuel

 

[Jochen Schmidt-Hambrock]

ProTools.

Before that, recording audio (multichannel with any quality) was a costly affair.

Jochen

 

[baro]

Film projectors commonly use three blade shutters these days, which raises the effective flicker period to 72Hz, and also on these models the film is advanced slightly more quickly, to fit with the smaller shutter angle - so maybe you have been watching films in theaters equipped with these?

Thanks for the information. Next time I will try to take a look at the type of the projector.