A few "naive" questions about frame rate perception

[MMhardKy]

I'm not a pro so my questions might sound a little bit naive, but since I began to be interested in digital video, I was always interested about the correlation of smoothness perception and the actual frame rate.

I know ofcourse that 24fps (or 25fps on PAL dvds) is the classic film look (which I like the most for any content), everything above 60fps seems almost reality-like etc.

My question is, why when I shoot with my HDV camcorder (Sony HC9) in 50i, it seems so smooth (soup opera like)? Is the interlaced image that recomposed to 50 frames per second (each frame with different content) and that is what is actualy displayed?
Does then each frame I can see contain information of 540 or 1080 lines?

Or is it in fact just 25 frames per second of information? Because if I watch it, the movements certainly feel much smoother, more like 50fps than 25fps...


And similiary with TV, if I watch digital cable (I live in PAL area) in 1080i, is it actualy 50 frames per second (each frame with different content what is displayed on the screen?

I would be so glad if someone could explain this stuff to me.

What I would like to do is to convert my 1080i50 video to a film-like framerate. In fact, once I had some problems with codecs on my HTPC and the video grabbed from my camera played back in what looked like 25fps instead of the classic "soap-opera" quality. Was my HTPC deinterlacing it and playing it back in 25p?

Sorry if my questions sound confusing and sorry for my english
thx

[Guest]

My question is, why when I shoot with my HDV camcorder (Sony HC9) in 50i, it seems so smooth (soup opera like)? Is the interlaced image that recomposed to 50 frames per second (each frame with different content) and that is what is actualy displayed?
Does then each frame I can see contain information of 540 or 1080 lines? It depends on what you play it with and how it is configured. Here are some possibilities:

1. You play it to a standard interlaced display, e.g., CRT TV. You get 50 fields per second with the full temporal resolution of the source.

2. You play it after single rate deinterlacing. You get 25 progressive frames per second with half the temporal resolution of the source.

3. You play it after double rate deinterlacing. You get 50 progressive frames per second with full temporal resolution of the source.

[iffybob]

The eye can see around than 20 fps, for most people, 50i , shows 25 full frames per second, (25 frames of odd lines, and 25 frames of even lines ), in an interlaced pattern, ( ie 1 even frame, then 1 odd frame, then 1 even frame , etc ), the eye does not see the the 1/50 of a second frame due to the reaction of the eye, what you see is a smoooooth transition from one frame to the rest, ie animation.

25 full frames a second is around the lowest level without you seeing a flickering picture, the higher frame rate you use the smoother and clearer the moving image looks, but you have to have the right souce and the right matching playback equipment.

If you display a 50 full fps on a standard crt TV ie 50 fps-interlaced , the playback equipment will send it a 50fps-interlaced signel, because the crt cannot display a full 50fps, though there are high refresh rate CRTs.

How your play back equipment converts 50 full fps to 25 full fps, is up to the maufacturer of the equipment.

[smok3]

What I would like to do is to convert my 1080i50 video to a film-like framerate

film-like framerate is a myth, i can tell you that things shot at 50p progressive can looks very 'filmic'.

[MMhardKy]

I am displayng it on an LCD in 1080p. The thing is, when I connect my 1080i camera to my LCD, the content looks very fluid, soap opera like. Kind off like when you enable all these fluid-motion things new LCDs have. The deinterlacing is done by my LCD, but I don't know exactly how. After it is deinterlaced, do I see 50 or 25 frames of content? I know the pixels are refreshing at 50hz, but I want to know if the stuff I see is 50fps where each frame is displayed for 0.02s or 25fps where each frame would be displayed at 0.04s ?

When I am playing the grabbed video via my HTPC (which outputs 1080p) it is sometimes as smooth as directly from my camera (if it is played trough descaler mpeg decoder), or not as fluid and more film like if I play it in windows media player (I don't know which decoder it uses, but there are no interlacing issues either).

Now I have loaded the video files into my main PC and am playing it through FFdshow.
Under deinterlacing in the control pamel, when I select for example "linear interpolation", the framerate looks "film-like". When I select "kernel bob", the framerate looks ultra smooth, like 50fps. What is actualy displayed?

How does my HDV 1080i camera actualy shoot? I have read that "each frame of interlaced video is composed of two fields that are captured at different moments in time".

EDIT: I thing I found the answer on 100fps.com:

"Do you think you record 25 frames per second when you make a movie with your digital camcorder?

Not quite.

Your digital camcorder does the following:
Records 50 pictures per second, intermixing every 2 consecutive pictures (with half the height) into 1 frame."


So the camera captures 50 images per second and if I select "kernel bob" deinterlacing under ffdshow, 50 images per second are displayed and that is why its so smooth. Am I right?

[MMhardKy]

film-like framerate is a myth, i can tell you that things shot at 50p progressive can looks very 'filmic'.

Could be, but for me, if I enable that "smooth motion" feature on my LCD, I cannot watch it because it turns a hollywood movie into a cheap soap opera (by rendering aditional frames).

[2Bdecided]

film-like framerate is a myth, i can tell you that things shot at 50p progressive can looks very 'filmic'.Well, professional maybe - but we're culturally conditioned to equate 25fps or 25p-in-50i (or, in the USA, 24p-in-60i) as film = high value.

I don't like it - but there's now so much fake filmic content on TV that even bad video (50i), converted to 25p, triggers some kind of subconscious response that 50i does not.

Cheers,
David.

[lqy]

Is 24 fps "film-like" ? Most movie projectors are double or triple shuttered so you get flicker at higher rate but repeated content. The theory is that blank frames inserted by the shutter help your vision to interpolate motion; also higher rate flicker is less perceivable.

I think you are confused about interlaced and progressive. 50i means 50 fields per second hence you can make a new and unique frame 50 times a second. That's going to look pretty smooth. The only problem is that if there is a fast moving object in high contrast with the background then you will see horrible combing artefacts. With 50p you won't get the combing.

The quote from 100fps.com is simply describing 50i. The deinterlacing is attempting to remove the combing artefacts.

[2Bdecided]

Is 24 fps "film-like" ? Most movie projectors are double or triple shuttered so you get flicker at higher rate but repeated content.PAL CRT TVs do the same, at 50Hz, but with fields rather than frames. Each original film frame is shown twice.

NTSC CRT TVs do it too, but with an irregular pattern (3-2).

The theory is that blank frames inserted by the shutter help your vision to interpolate motion;No they don't - quite the opposite - showing a single frame twice gives an objectionable double image on the retina when it tracks on-screen motion, rather than a less objectionable blured image.

also higher rate flicker is less perceivable.Yes, true.

I think you are confused about interlaced and progressive. 50i means 50 fields per second hence you can make a new and unique frame 50 times a second. That's going to look pretty smooth. The only problem is that if there is a fast moving object in high contrast with the background then you will see horrible combing artefacts.50i doesn't give combing effects on an interlaced display. Never.

If you show the frames in their entirety (progressively), then of course you'll see combing, but you won't see smooth movement either!

With 50p you won't get the combing.Of course not. You can't get combing with a progressive source (except eye tracked motion when viewing progressive content on an interlaced display, usually only when sitting too close).

Cheers,
David.

[smok3]

Could be, but for me, if I enable that "smooth motion" feature on my LCD, I cannot watch it because it turns a hollywood movie into a cheap soap opera (by rendering aditional frames).

i was refering to stuff shot at 50p, not to some DSP...

[lqy]

PAL CRT TVs do the same, at 50Hz, but with fields rather than frames. Each original film frame is shown twice.

NTSC CRT TVs do it too, but with an irregular pattern (3-2).


You are comparing progressive with interlaced when I was talking about progressive. CRT TVs do not show images twice unless that is input and in the case of NTSC pulldown fields are repeated. A movie projector will repeat the same frame 2 or 3 times, progressive.


No they don't - quite the opposite - showing a single frame twice gives an objectionable double image on the retina when it tracks on-screen motion, rather than a less objectionable blured image.


There is no double image on the retina but linear motion on the screen may appear nonlinear.

LCD displays also repeat frames, it's called "black frame insertion".


50i doesn't give combing effects on an interlaced display. Never.

If you show the frames in their entirety (progressively), then of course you'll see combing, but you won't see smooth movement either!


Yes, but fields are only half an image.

IMHO the "filmic quality" the OP desires is more to do with choice of camera lenses and colour processing used in movie production than frame rate or interlacing.

[um3k]

There is no double image on the retina but linear motion on the screen may appear nonlinear.

I would have to say, from my personal experience, there most certainly is a double image effect when one attempts to visually track a moving object on a movie screen. I find it kind of annoying, myself. But it's better than getting a headache from watching 24hz flicker.

[iffybob]

I would have to say, from my personal experience, there most certainly is a double image effect when one attempts to visually track a moving object on a movie screen. I find it kind of annoying, myself. But it's better than getting a headache from watching 24hz flicker.

is this just at the/a movie/cinama screen or on all play back screeens, with the same source ?

or is it bad visual effects processing, and you notice ?:rolleyes:

[um3k]

Primarily on cinema screens. It's much less noticeable on TVs since they are smaller and tracking doesn't occur as often.

[lqy]

When you say "double image effect" I think most people assume you mean two images offset from each other.

When you see two images at the cinema it is because of double shuttering. With fast motion then you get motion judder because of the nonlinear sequence: movement-hold-movement-hold-...

That's why modern TVs have frame rate conversion, to "undo" pulldown and insert interpolated frames thus eliminating any frames with hold.

[2Bdecided]

...and in those "movement-hold" sequences you certainly do get double images on your retina when your eye tracks the motion.

Cheers,
David.

[Soulhunter]

film-like framerate is a myth, i can tell you that things shot at 50p progressive can looks very 'filmic'.
Doesn't it depend on the shutter-speed? I mean, if you use a slow'ish shutter-speed, even 100fps footage should look film-like as you'll introduce film alike motion blur, no? Also, even 24fps can look non-film-like by using a faster shutter speed (one example that comes to my mind are some fighting scenes in the movie Gladiator).

Is 24 fps "film-like" ? Most movie projectors are double or triple shuttered so you get flicker at higher rate but repeated content. The theory is that blank frames inserted by the shutter help your vision to interpolate motion; also higher rate flicker is less perceivable...
Don't mix up filming/recording and playback... Adding blank frames while playback just reduces the flicker, but it doesn't change the look of the footage/motion as a different frame-rate/shutter-speed while recording/filming would!