PMW-350 1080/25p vs 1080/50i

[Kalunga Lima]

I'm about to start a doc with a new PMW-350 together with a Nanoflash unit. While testing the camera I encountered significant motion artifacts in 1080/25p, which seem to go away in 50i. Can anyone tell me the advantage of 1080/25p over 1080/50i?

Tanx

[Duncan Craig]

Have you tried 1/50th second shutter speed when in 25p?

[Bruce Rawlings]

Another tip picked up from Alister Chapman I think. Use 180 degree shutter, this makes the pictures look very good.

[Duncan Craig]

180 degrees and 1/50th second at 25p are the same thing.

[Bruce Rawlings]

When set to 180 the value follows whatever changes you make later.

[David Issko]

I haven't used 25p for about a year now (EX3 & now PMW). I cannot stand the jerkiness of 25p. It's ok for the NTSC area people who use 30p. I tried 30p as a test and there isn't the jerkiness associated with 25p. I live in a PAL area and as such I keep to the PAL frame rates.

Many of you will disagree with me, and that's all about this great forum, but for me, and my projects, its 50i all the way.

I haven't even switched my PMW to 25p. I set it to 50i on initial switch on and it has stayed on 50i since. No, my clients do not know that 50i & 25p even exist.

It has been stated that 25p is the best rate for creating video for the net. Many of my 50i projects are on the net by way of YT & embedded within clients' websites created & finished in 50i. No problem.

Kalunga, there isn't anything you can do about the jerkiness in 25p, except keep panning & tilting rates to within certain speeds. With all due respect to the other posters above, what they failed to mention is that when you change the shutter speed to a higher value, you lose exposure. Maybe this is because the PMW-350 is such a sensitive camera, a little light loss isn't a big deal under most lighting conditions. The fact remains that motion jerkiness is a fact of life with 24p & 25p.

Comments please.

[Simon Wyndham]

I cannot stand the jerkiness of 25p.

A none issue really. I realise a lot of people hate it, but if you see European video on YouTube or Vimeo it will be 25p and whenever you see a film at the cinema it is 24fps. Ideally we could shoot at 50p 1080 and we could make the decision in post whether to go for the filmlook etc.

But the fact is that 25p *is* by far the most versatile format, at the moment. It can easily be converted to 24p.

50p would be better though. And the US should convert to 50hz electric supplies to save hassle for the rest of us ;)

[Mike Marriage]

Originally Posted by Simon Wyndham

And the US should convert to 50hz electric supplies to save hassle for the rest of us ;)

I agree - although I don't expect them to change their entire electrical grid, just their frame rate - modern screens can cope with a range of frame rates independent of the electrical frequency. I think the world should standardize on 25p and 50p.

Modern LCDs, plasmas and computer monitors are also better suited to progressive video. Interlace video is effectively an old system of "analogue compression" and does not suit modern digital compression or screens.

I shoot 1080p25 for "filmlook," ie drama, high end doc work, filmouts and if I need the "live TV look" I tend to use 720p50 as it downscales better to SD and is more compression friendly. I've seen all sorts of strange things happen to interlace video on the web, although it can look fine if handled correctly.

[Christopher Young]

Yes most film is shot at 24fps but we mustn't forget that cinema film projectors for some years now have used the Maltese cross movement with shutters that are designed with a flicker-rate of two times, i.e. 48 Hz, or even sometimes three times, 72 Hz, way above the 24fps shooting frame rate of the film. This reduces the perception of screen flickering and shudder on pans especially. At 48hz each frame is shown twice that's why cinema film projection looks way smoother than the jerky movement associated with 25p. IMHO 25p doesn’t look anything like film at 48Hz, which is in reality film's version of 48p if speaking in video terms. At 48Hz this is close to the holy grail of 50p or 60p. 50p projection looks much, much closer to modern 48Hz film projection. Hence 50i or 60i looks much smoother.

[Piotr Wozniacki]

Originally Posted by Christopher Young

Yes most film is shot at 24fps but we mustn't forget that cinema film projectors for some years now have used the Maltese cross movement with shutters that are designed with a flicker-rate of two times, i.e. 48 Hz, or even sometimes three times, 72 Hz, way above the 24fps shooting frame rate of the film. This reduces the perception of screen flickering and shudder on pans especially. At 48hz each frame is shown twice that's why cinema film projection looks way smoother than the jerky movement associated with 25p. IMHO 25p doesn’t look anything like film at 48Hz, which is in reality film's version of 48p if speaking in video terms. At 48Hz this is close to the holy grail of 50p or 60p. 50p projection looks much, much closer to modern 48Hz film projection. Hence 50i or 60i looks much smoother.

One mustn't forget that most of our 25p productions being watched now at flat screens (like the plasma or LCD HDTV sets), each frame is usually also displayed at least twice (with sets scanning at 50 Hz), 4 times (with 100 Hz refresh rate). 200 Hz is now becoming most popular...

[Simon Wyndham]

IMHO 25p doesn’t look anything like film at 48Hz, which is in reality film's version of 48p if speaking in video terms.

Chris, each frame may be displayed twice with film projection, but that doesn't change the perception of movement or the cadence. The film was captured at 24fps and is still shown at that speed. You can't smooth out motion simply by showing each frame twice.

Besides, since I'm feeling pedantic, 25p is shown at 50hz on a television, or even higher these days. But there are still only 25 frames per second captured by the camera, just as there are only 24 frames per second captured by most film cameras.

Showing 24 fps film at 48fps display rate by showing each frame twice is absolutely *nothing* at all like 48p or 48fps.

The reason why film appears slightly less jerky than 25p or 24p video is due to the a) the settings on the camera, and b) the settings on the TV. The settings I am referring to are those to do with the detail settings. Simply put, and I'm not going to go into it yet again in detail because I have done so on these forums ad nauseum in the past so do a search, the more artificial edge enhancement there is, the more high frequency edges there are, and the perception of jerkiness is greater.

[Mike Marriage]

Also most 24p filmouts you see on the big screen are shot by DPs experienced enough to avoiding pans that would cause "jerkiness." 25p video isn't always shot with such care.

[David Issko]

Originally Posted by Simon Wyndham

A none issue really.

50p would be better though. And the US should convert to 50hz electric supplies to save hassle for the rest of us ;)

Party pooper Simon!!!! :) I was hoping for some lively debates. Oh yes, 50p would be GREAT. I would not hesitate after seeing how nice 30p is.

You are right, let's lobby the US to go 50Hz.

Cheers!

[David Issko]

Originally Posted by Mike Marriage

Modern LCDs, plasmas and computer monitors are also better suited to progressive video. Interlace video is effectively an old system of "analogue compression" and does not suit modern digital compression or screens.

I shoot 1080p25 for "filmlook," I've seen all sorts of strange things happen to interlace video on the web, although it can look fine if handled correctly.

Thank you for your response Mike. Great to read another shooter's viewpoints. From a technical point of view, I can, in part, agree with your post. However, in the real world, some of your insightful comments may not always be correct. As an example:

My Pioneer full HD plasma, my main editing monitor displays my 50i recording with the quality and finesse that Pioneer is renowned for. Smooth as silk and sharp, but not artificially so. It also displays the converted SD as best as SD can be displayed.

I had posted yesterday about an associate having major issues with compressing his HD material to SD. He shot in 25p with his EX1. My interlaced HD compresses to SD (and on to DVD0 brilliantly). No digital issues there.

50i works for me and my clients in many ways an until I can achieve better, I am sticking with it.

Lastly, there is a misunderstanding about 25p (or 24p or 30p) on its own being the filmlook. Doesn't the camera need a specific lens to achieve the filmlook proper? To me, 25p - setting aside the jerkiness of movement - looks 'thinner' to my eyes (and brain) than film. No doubt many film makers have been debating very hard against the 'p' film look (from video cameras) comparison.

Cheers Mike.

[Christopher Young]

Originally Posted by Simon Wyndham

The reason why film appears slightly less jerky than 25p or 24p video is due to the a) the settings on the camera, and b) the settings on the TV. The settings I am referring to are those to do with the detail settings. Simply put, and I'm not going to go into it yet again in detail because I have done so on these forums ad nauseum in the past so do a search, the more artificial edge enhancement there is, the more high frequency edges there are, and the perception of jerkiness is greater.

Simon. I agree with what you say but the way you state it is but a part of the answer. It a much more complicated issue than 'Simply put'. My reply is long and even in it's length it barely touches on the subject of '25p looking jerky'. I think there are some who may desire a more detailed explanation.

Most moving images depend on presenting a rapid succession of static images such as film frames or video frames. Flicker Fusion is one of the many important contributing factors in understanding the whys and wherefore of why we perceive flicker or jerkiness or judder in the viewing of any frame based vision. Specifically at certain frame rates commonly used in video such as 25 and 30p. As an aside interlace video was a convenient way of getting away from this problem plus at the time it was introduced it allowed narrower spectrum bandwidth transmission. As it still does today because to transmit 50p would take more transmission spectrum than most governments are prepared to allow.

If we take the average cinema lighting level, at around 30-50cd/m2 we have a very low flicker fusion threshold with film displayed at 48 exposures a second. Because of this low threshold the film display frame rate at 48Hz along with 30-50cd/m2 light levels makes the resultant moving image look pretty smooth.

As you point out regardless of how the moving image is displayed the ‘cadence’ is not going to alter. Where the apparent jerkiness of 25p comes from is that on most television displays we watch at home or look at in the edit suite, be they CRT, LCD or Plasma and running at anywhere between 50 to 600 Hz they are commonly viewed at levels around and quite often well above 200 and up to 500cd/m2.

Another contributing factor. With regard to the fact that the video was shot, at lets say 25p, and subjectively still looks worse in movement than 24fps film is in large part due to the fact that most modern video cameras can’t emulate the temporal response of film. I amongst many, including yourself, have tried to emulate film characteristics by reducing the detail and enhancement circuits of modern HD cameras to try to overcome the tendency of modern HD video cameras to enhance mid frequency resolution. By reducing these detail parameters one can go some way to emulating film’s look because these ‘reductions’ (sometimes quite well in to negative settings) subjectively minimise jerkiness. This is subjective observation only.

Objectively though 25p will never truly emulate film’s spatio-temporal movement because the way you achieve a 180-degree film camera shutter emulation in a CCD camera (CMOS I’m not sure yet but I suspect much the same) is achieved in a manner totally different to that in a film camera. Most modern video cameras use electronic shutters, with the notable exception of the earlier Bosch FT CCD LDKs that used mechanical rotating ones. Film cameras generally use a rotating mechanical shutter.

A good extract that helps outline one of the reasons there is a difference between film and video:

“Typically, the shutter is open for 50% of the frame duration of 1/24 second, and it is usual to express this in degrees as a 180-degree shutter. Video cameras more often use an electronic mimic of the shutter. They achieve their ‘shutter’ by allowing the light-induced charge to accumulate in the CCD and then dumping it all at the appropriate time BEFORE the CCD is read, allowing the CCD then to continue accumulating charge for the wanted period. With this type of electronic shutter a video camera’s exposure is always taken during a period that finishes at the END of an image interval, instead of in the MIDDLE as in film.” (A. Roberts. BBC R&D WHP 034)

Question then is what happens to the image motion that took place during the first 50% charge of the CCD frame capture that was ‘dumped’. Simply put it’s gone forever. The same exposure for the 180-degree film shutter encompasses all the movement that took place during the recording of that frame’s duration. This again contributes to the subjective difference in intra-frame movement between that of 24fps film and 25p video
.
Combine the frame rate of 25p with its video spatio-temporal and electronic shutter characteristics with a high flicker fusion rate viewing level of 200 to 500cd/m2 and in most cases it will look jerky compared to film. As an experiment sit in a room with lights you can dim right down and now view your 25p footage with the brightness and contrast turned right down on your display panel and I think you will be quite amazed how much smoother your vision will look especially if your room lights are at a lower level than your display’s brightness. In other words conditions similar to those you encounter in a cinema.

In other words in film or video If the frame rate falls below the flicker fusion threshold for the given viewing conditions, flicker will be apparent to the observer, and movements of objects on the film or video will appear jerky. For the purposes of presenting moving images, the human flicker fusion threshold is usually taken as 16 Hz. Most movies are recorded at 24 frames per second, and most video cameras operate at 25 or 30 frames per second, depending on the video system used.

Even though motion may seem to be continuous at 25 or 30 frames, the brightness may still seem to cause objectionable image movement. By showing each frame twice in cinema (48Hz projection), and using the interlace scanning in television (50 or 60 Hz), a reasonable margin of error for unusual viewing conditions is achieved in minimising subjective flicker and movement effects.

All of the latest developments in high refresh rate 100~600Hz flat panel displays available today have come about to overcome a) the high brightness viewing levels many people watch their sets in and b) the spatio-temporal and electronic characteristics of the video camera. The result being manufactures are having some success in trying to overcome the flicker fusion threshold with high refresh rates for 24~25~30p based vision.

In the foreseeable future no amount of development though is going to overcome the inherent differences in that spatio-temporal and shutter differences between film and video cameras hence 25p and 30p video cadence will never look the same as film at 24fps.