60Hz to 48Hz for analog television

roxics

roxics

Veteran
Just a hypothetical, but how difficult would it have been to change a 60Hz electrical signal into a 48Hz television signal?
I'm just thinking about the history of television in the U.S. and how we had to do do these frame rate conversions between film and video. So would it not have been easier to just have televisions operating at 48Hz and frame rates of 24fps/48fields per second? It certainly would have saved us on video tape and allowed us to fit a higher resolution picture into the same bandwidth like they did with PAL.

Why was this not the solution?
 
Pal 25 frame displayed at 50i is bad enough. Quite a few people can discern a flicker with PAL TV at 50Hz. 48Hz would be even worse. At the USA mains frequency of 60Hz with 60i transmissions of 30 frames a second the frame rate is far enough removed from the persistence of human vision not to cause any flicker issues for the bulk of the population. The other consideration is that any of the interlace transmissions methods introduced a 50% drop in vertical resolution. The bandwidth required to transmit OTA signals in progressive mode meant that the spectrum bandwidth that was allocated to broadcasters made the uptake of progressive transmission impractical. As we all well know 24 FPS in the cinema is displayed at 48, 72, or 96 FPS to avoid the 24 frame judder on quick movement. Hence 24 and 25p footage doesn't have the correct cadence on a PC monitor... as much as many people may say "Ah! The cinematic look."

Chris Young
 
cyvideo said:
Pal 25 frame displayed at 50i is bad enough. Quite a few people can discern a flicker with PAL TV at 50Hz. 48Hz would be even worse. At the USA mains frequency of 60Hz with 60i transmissions of 30 frames a second the frame rate is far enough removed from the persistence of human vision not to cause any flicker issues for the bulk of the population. The other consideration is that any of the interlace transmissions methods introduced a 50% drop in vertical resolution. The bandwidth required to transmit OTA signals in progressive mode meant that the spectrum bandwidth that was allocated to broadcasters made the uptake of progressive transmission impractical. As we all well know 24 FPS in the cinema is displayed at 48, 72, or 96 FPS to avoid the 24 frame judder on quick movement. Hence 24 and 25p footage doesn't have the correct cadence on a PC monitor... as much as many people may say "Ah! The cinematic look."

Chris Young
Click to expand...

Thank you. Honestly I always forget that it's not a straight 24fps we're seeing. But is that also true in the digital space on newer progressive TVs and computer displays?

What would have been a good solution for this aside from the one we had with NTSC? In other words, if you had to go back and reinvent television and make it compatible with film, how would you do it? Assuming we all love the 24fps look of film. Just to give you more flexibility in this hypothetical question, you can also redesign the US power grid if that helps.
 
cyvideo said:
As we all well know 24 FPS in the cinema is displayed at 48, 72, or 96 FPS to avoid the 24 frame judder on quick movement. Hence 24 and 25p footage doesn't have the correct cadence on a PC monitor... as much as many people may say "Ah! The cinematic look."
Click to expand...

When I read about the shutter of a film projector opening and closing a few times per frame, the book said that it was to reduce flicker, not judder. (I guess somehow it smooths out the brightness level over time.)

I also remember in film theaters that pans had quite a bit of judder. The only thing that would reduce judder, in my understanding, is more information (more frames).
 
combatentropy said:
When I read about the shutter of a film projector opening and closing a few times per frame, the book said that it was to reduce flicker, not judder. (I guess somehow it smooths out the brightness level over time.)

I also remember in film theaters that pans had quite a bit of judder. The only thing that would reduce judder, in my understanding, is more information (more frames).
Click to expand...

the projection speeds will have an effect on motion judder. On hi-speed pans, many people can see a slight amount of judder, rather I should have said choppiness as opposed to judder at 48Hz. At 72 and 96Hz it becomes pretty imperceptible. And yes flicker. Flicker is diminished at the higher projection rates. An image flashed onto the retina dies in about 1/20 of a second. At a refresh rate of 1/24 of a second, the image from the previous frame is well and truly fading down in the mind's eye before it gets refreshed hence the observed flicker. More frames per second. You are correct. In effect that is what you are doing when projecting every frame twice at 48 fps on 24 fps film. The eye is now seeing 48 flashes, frame exposures per second. Most common or garden PC monitors refresh at 60Hz so 24 and 25p look pretty ordinary compared to the double and triple exposures rates of cinema. That is why most modern TVs have scan rates anywhere up to 200Hz or so. Plus many TVs have something along the lines of Panasonic's" Intelligent Frame Creation" option in the menu. Where you can turn it off and watch 24p film at 24p. Or you can dial it up to the max where in effect it is creating interpolated frames to smooth the action. Video shot at 50 and 60p and displayed on PC screens is becoming more popular as it is for the average viewer more akin to 'normal TV' viewing i.e. 50i and 60i terrestrial transmissions. A good example can be seen here with the different frame rates when observed on a PC screen. If I get a client that's not happy with the end result of 24 or 25p footage when they see their final production edited I'll use RE:Vision's RSMB to impart a more cinema look experience to 24 and 25p footage for display on PC screens. Check out some of the video examples on their page below.

Chris Young


RE:Vision RSMB

https://www.toolfarm.com/buy/reelsma...after_effects/
 
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roxics said:
Thank you. Honestly I always forget that it's not a straight 24fps we're seeing. But is that also true in the digital space on newer progressive TVs and computer displays?
Click to expand...

I kind of covered that in my response to combatentropy's post

roxics said:
What would have been a good solution for this aside from the one we had with NTSC? In other words, if you had to go back and reinvent television and make it compatible with film, how would you do it? Assuming we all love the 24fps look of film. Just to give you more flexibility in this hypothetical question, you can also redesign the US power grid if that helps.
Click to expand...

Joking. I would go further back and start film off at 48, 50 or 60p fps and this topic of "cinematic 24p look" would never have arisen in later years. :)

Chris Young
 
So if we're watching 24fps footage as is on modern TVs and computer displays, why is that not an issue but being on a CRT display at 48Hz would be?
Is it just the way the interlacing works that would make it look worse?
Personally I have no issues with 24p on TVs and computer displays. So if that's the way it would look on a 48Hz CRT, I guess it's just subjective.
 
roxics said:
So if we're watching 24fps footage as is on modern TVs and computer displays, why is that not an issue but being on a CRT display at 48Hz would be?
Is it just the way the interlacing works that would make it look worse?
Personally I have no issues with 24p on TVs and computer displays. So if that's the way it would look on a 48Hz CRT, I guess it's just subjective.
Click to expand...

CRTs. I love a good one. I had a Sony KV-HR36M31 for home viewing. That was Sony's Hi-end 1920x1080 super fine pitch CRT which had grade 2 broadcast phosphors. Considered by many to be one of the best CRTs ever offered on the retail market. CRT's basically operate at the speed of light,186.000 mph so writing to the screen is basically instantaneous. The phosphors in high quality CRT monitors are designed to deliver a specific decay curve after being excited by an electronic beam. So it was a progressive decay of the light seen by by the observer as opposed to discreet pixels that are switched on and off. Hence a much 'smoother' viewing experience. When I closed my studio down I got cleaned out of all my high end PVM and BVM Sony CRT monitors, about a dozen off them by fanatical gamers. Go figure that one. Gamers love them. As you say... it's all subjective. Depends on what you are used to and what floats your boat. For those who never really experienced hi-end CRTs they'll never know the difference. Even as basic REC 709 as they were.

Chris Young
 
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