Jump to content


Photo

shutter/motion artefact question


  • Please log in to reply
23 replies to this topic

#1 Dean Braybrooke Gray

Dean Braybrooke Gray

    New

  • Basic Members
  • Pip
  • 8 posts
  • 2nd Assistant Camera
  • London

Posted 27 August 2009 - 05:12 PM

Hi there,

Are there any negative points to using the shutter as a type of ND when you want to shoot wide open. I know that shutter speeds 1/25 or below introduces motion artefacts, but i was wondering if there are any negatives when using higher shutter speeds (when shooting Interlace i should add)

I was assisting today using the Sony DVW790 shooting 50i, and this is what the camera operator did to get to f1.8, 1/125 was the shutter speed. I've always used ND filters or in camera filters, but I've noticed several operators use the shutter to achieve the same effect as an ND, and wondered if this has any undeserible effects which may only become apparent when broadcast?

Cheers

Dean
  • 0

#2 Thomas James

Thomas James
  • Basic Members
  • PipPipPipPip
  • 844 posts
  • Camera Operator

Posted 27 August 2009 - 11:09 PM

You should never shoot interlace because interlace is obsolete and produces a lot of undesirable artifacts. You should instead shoot 50p progressive scan high definition video instead of 50i.
  • 0

#3 Brian Drysdale

Brian Drysdale
  • Basic Members
  • PipPipPipPip
  • 5070 posts
  • Cinematographer

Posted 28 August 2009 - 03:35 AM

You should never shoot interlace because interlace is obsolete and produces a lot of undesirable artifacts. You should instead shoot 50p progressive scan high definition video instead of 50i.


You'd better tell the BBC that, they use 1080 50i for their HD transmissions.

With the higher shutter speeds you get a "Saving Private Ryan" effect and you lose the motion blur which smooths the action. Even shooting interlace you get this effect, perhaps not so noticeable up to 1/120, but it does greatly increase the faster the action and shorter the shutter time.
  • 0

#4 Thomas James

Thomas James
  • Basic Members
  • PipPipPipPip
  • 844 posts
  • Camera Operator

Posted 28 August 2009 - 04:48 AM

The problem is that there is a legacy of interlace video when over 70 years ago the BBC banned a perfectly good progressive scanning system which was invented by Baird in favor of the interlace system. Is the BBC going to admit that they were wrong for all these years?
  • 0

#5 Brian Drysdale

Brian Drysdale
  • Basic Members
  • PipPipPipPip
  • 5070 posts
  • Cinematographer

Posted 28 August 2009 - 08:38 AM

The problem is that there is a legacy of interlace video when over 70 years ago the BBC banned a perfectly good progressive scanning system which was invented by Baird in favor of the interlace system. Is the BBC going to admit that they were wrong for all these years?


I suspect the reason why they (and all other broadcasters) went for an interlace system was the lower bandwidth requirements compared to having a progressive system. That could also be the reason why they're still using it for their 1080 HD channels.

Sometimes you have to make trade offs and so far 720 is the only broadcast HD progressive format. I guess the digital distribution networks like to squeeze in a few more channels of stuff you've already seen into that space.
  • 0

#6 Dean Braybrooke Gray

Dean Braybrooke Gray

    New

  • Basic Members
  • Pip
  • 8 posts
  • 2nd Assistant Camera
  • London

Posted 28 August 2009 - 10:03 AM

You should never shoot interlace because interlace is obsolete and produces a lot of undesirable artifacts. You should instead shoot 50p progressive scan high definition video instead of 50i.

Supposing your asked to deliver coverage of an event such as a grand prix in standard definition (excusing all the logistics involved in such a scenario) you would shoot 25P over 50i ?!
  • 0

#7 Chris Keth

Chris Keth
  • Sustaining Members
  • 4427 posts
  • 1st Assistant Camera
  • Los Angeles

Posted 28 August 2009 - 11:05 AM

I think it's a terrible idea. You do that all day and your days work ends up a mess of a half-dozen different shutter speeds. I prefer ND.

That said, some of the world's top reality operators I've worked with do it without thinking twice.
  • 0

#8 Dean Braybrooke Gray

Dean Braybrooke Gray

    New

  • Basic Members
  • Pip
  • 8 posts
  • 2nd Assistant Camera
  • London

Posted 28 August 2009 - 12:11 PM

I think it's a terrible idea. You do that all day and your days work ends up a mess of a half-dozen different shutter speeds. I prefer ND.

That said, some of the world's top reality operators I've worked with do it without thinking twice.


We already had ND filter wheel 2 in, ND 3 was too bigger stop loss, but a 1/125 shutter speed seemed to equal that final 1 & 1/2 stops we needed to lose, allowing the op to open up to f1.8, it was a sit down interview incidentally.
I've always heard conflicting opinions on this from really experienced operators! I'm guessing, rule of thumb would be to only apply shutter as a form of ND when your shooting in controlled conditions with minimal subject/object movement, and when your ND tools have all been exhausted! Thanks for everyone opinions :lol:
  • 0

#9 Thomas James

Thomas James
  • Basic Members
  • PipPipPipPip
  • 844 posts
  • Camera Operator

Posted 28 August 2009 - 12:47 PM

Interlace scanning does not lower bandwidth requirements. Progressive scanning is the most efficient use of bandwidth for both analog and digital broadcasts. What interlace scanning does it to artificially boost up the resolution numbers. 1080p50 uses the exact same bandwidth as 1080i60 and 1080p50 uses only 20 percent more bandwidth than 1080i50 yet the BBC says it can't afford 1080p50 sports broadcasts?


Broadcasters in the United States use the 1440X1080i format rather than 1920x1080i in order to save bandwidth. So if the BBC wants to save bandwidth wouldn't 1440x1080p50 be better than 1920x1080i50?
  • 0

#10 Brian Drysdale

Brian Drysdale
  • Basic Members
  • PipPipPipPip
  • 5070 posts
  • Cinematographer

Posted 28 August 2009 - 02:47 PM

This explains the advantages and disadvantages of interlace.

http://en.wikipedia.org/wiki/Interlace
  • 0

#11 Thomas James

Thomas James
  • Basic Members
  • PipPipPipPip
  • 844 posts
  • Camera Operator

Posted 28 August 2009 - 03:10 PM

I would have to disagree with the article . There are no advantages to interlacing. Interlacing damages picture quality and it wastes bandwidth. The only advantage to interlacing is that it artificially boosts resolution. So that means that interlacing is a marketing success and a picture quality failure because most people will refuse to buy progressive scan camcorders because they think that interlace 1080i is higher quality than 720p.

If you look at the Wikepedia article it includes animations that demonstrate the horrible artifacts that interlace scanning produces which is called interline twitter. These artifacts are simply unacceptable. Yet the proponents of 1080i trash the 720p format and refuse to recognize 720p as full high definition.
  • 0

#12 Brian Drysdale

Brian Drysdale
  • Basic Members
  • PipPipPipPip
  • 5070 posts
  • Cinematographer

Posted 28 August 2009 - 04:04 PM

I think most people accept 720p as high definition. Although this has nothing to do with the DVW790 Digi Beta camera being used on this particular shoot, which only shoots interlaced PAL and I assume production is being broadcast SD in the UK.

I think you're throwing in the perceptions of HDV camera specs.
  • 0

#13 Thomas James

Thomas James
  • Basic Members
  • PipPipPipPip
  • 844 posts
  • Camera Operator

Posted 28 August 2009 - 05:18 PM

I thought that the camera was the Sony F700 high definition camera. The HDV 1440x1080i specifications are actually MPEG-2 over the air broadcast specifications used in the United States. Although the Federal Communications Commision specifies the 1920x1080i format this is never used because it produces objectionable artifacts.
  • 0

#14 Thomas James

Thomas James
  • Basic Members
  • PipPipPipPip
  • 844 posts
  • Camera Operator

Posted 28 August 2009 - 05:34 PM

Most people may recognize 720p as an entry level high definition format however most people insist that only 1080i can be called full high definition. This thinking is totally bogus because progressive scan 720p is superior in every way to interlace 1080i however most people can not think outside the box and automatically assume according to their common sense that higher numbers always mean better picture quality.

Edited by Thomas James, 28 August 2009 - 05:35 PM.

  • 0

#15 Brian Drysdale

Brian Drysdale
  • Basic Members
  • PipPipPipPip
  • 5070 posts
  • Cinematographer

Posted 29 August 2009 - 04:26 AM

I thought that the camera was the Sony F700 high definition camera. The HDV 1440x1080i specifications are actually MPEG-2 over the air broadcast specifications used in the United States. Although the Federal Communications Commision specifies the 1920x1080i format this is never used because it produces objectionable artifacts.


The opening post quite clearly states a "Sony DVW790".

The EBU appears to prefer 1080 p25, although they seemed to be in the 720p camp before.

http://www.ebu.ch/en...-editorial.html

The BBC has gone the interlace route at a resolution of 1440x1080i, encoded in MPEG-4 H.264/AVC.

I believe this may explain their arguements.

http://www.digitalra...080i-for-HD.php

At the back of their minds may be that increase in static resolution from PAL to 720p isn't that great compared to 1080i. Although the vertical resolution between 720p and 1080i is more or less the same, the horizontal is improved on 1080. The rights and wrongs of this decision can be argued about, but it's currently in place. A lot of UK HD material is shot at 25p rather than interlace.

In the UK shops the 1080 screens appear to be replacing the 720.
  • 0

#16 Thomas James

Thomas James
  • Basic Members
  • PipPipPipPip
  • 844 posts
  • Camera Operator

Posted 29 August 2009 - 12:26 PM

Of course you can keep listening to bogus arguments from the BBC that claims that interlacing 1080i is better than progressive scan 720p.
First of all let us examine how many pixels each format delivers. 1440x1080x25 =39 million pixels per second. 1280x720x50 = 46 million pixels per second. This means that the 720p format actually has 20 percent more pixels than 1080i. Yet the BBC says that only 1080i is true high definition. What a rip off.
The reason why the BBC is going with 1080i is pure and simple. Even though 1080i is a picture quality failure it is indeed a marketing sucess because consumers are duped into believing that 1080i has better picture quality because of the higher number.
  • 0

#17 Brian Drysdale

Brian Drysdale
  • Basic Members
  • PipPipPipPip
  • 5070 posts
  • Cinematographer

Posted 29 August 2009 - 02:33 PM

I don't think the BBC is saying anything about 720p not being HD, their natural history unit used it for a number of productions. They just decided that 1080i was the best option for them, since 1080 p50 would take up too large a bandwidth and sport coverage would be unacceptable at 25p. Marketing is part of any decision making process.

Their argument is based on static resolution, I'm not sure how "pixels per second" would affect something that isn't moving. Your figures would suggest a lower bandwidth requirement for 1080i over 720p50, which could also be a factor in their decision.

Regardless, I'm not defending the BBC, they do things their own way, which can vary between the very sensible or totally eccentric In the real world I can only work with the transmission formats used by the broadcasters and I usually shoot 25p for HD anyway.
  • 0

#18 Thomas James

Thomas James
  • Basic Members
  • PipPipPipPip
  • 844 posts
  • Camera Operator

Posted 29 August 2009 - 03:59 PM

The BBC may not have said that 720p is not high definition however there is a barage of false advertising by camera equipment manufacturers that claim 1080i is full high definition which it is most certainly not.

As far as the 1080p50 format taking up too much bandwidth it should be noted that progressive scan offers the most efficient use of digital compression technology. The additional bandwidth requirements of 1080p50 over 1080i50 would only be about 20 percent greater. However this additional bandwidth requirement is only suggested in order to take full advantage of the greater picture quality of 1080p50. Therefore it could be argued from a purely practical point of view that the 1080p50 format would give a satisfactory picture even if no additional bandwidth were allocated.
  • 0

#19 Brian Drysdale

Brian Drysdale
  • Basic Members
  • PipPipPipPip
  • 5070 posts
  • Cinematographer

Posted 29 August 2009 - 04:25 PM

I think it's generally accepted that 1080i is HD, however, you're entitled to a personal opinion that it's not.

Regarding the 20/% extra for 1080p 50, not using that 20% means that more HD channels can be squeezed in.
  • 0

#20 Thomas James

Thomas James
  • Basic Members
  • PipPipPipPip
  • 844 posts
  • Camera Operator

Posted 29 August 2009 - 06:49 PM

This is not my personal opinion but rather comes from the original International Telecommunications Union ITU specifications that states that a high definition format must have greater temporal resolution than standard definition. In order for 1080i to meet ITU specifications it would have to operate at a scanning rate of at least 100 fields per second which would then be called 1080i100. Because there was a lot of legacy 1080i equipment that did not meet ITU specifications the ITU decided to grandfather in the 1080i format. Unfortunately as soon as this obsolete 1080i format was grandfathered in marketers lied and claimed that 1080i was the next generation high definition format designed to supplant 720p. The truth is that is was just the opposite because 720p progressive scan high definition was designed to supplant and to make obsolete 1080i.

Using 1080p50 progressive scanning does not mean that there has to be less channels available. As I have said before if more channels are desired 1080p50 can use exactly the same bandwidth as 1080i50.
  • 0


Broadcast Solutions Inc

The Slider

Ritter Battery

Abel Cine

Rig Wheels Passport

CineLab

Gamma Ray Digital Inc

Technodolly

Metropolis Post

Wooden Camera

Visual Products

Opal

rebotnix Technologies

Tai Audio

Media Blackout - Custom Cables and AKS

FJS International, LLC

Aerial Filmworks

Glidecam

Paralinx LLC

Willys Widgets

CineTape

Rig Wheels Passport

Broadcast Solutions Inc

Tai Audio

FJS International, LLC

CineTape

Wooden Camera

rebotnix Technologies

Paralinx LLC

Ritter Battery

Gamma Ray Digital Inc

CineLab

Aerial Filmworks

Technodolly

Glidecam

Media Blackout - Custom Cables and AKS

Metropolis Post

The Slider

Abel Cine

Opal

Visual Products

Willys Widgets