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50i vs 25p

50i 25p frame rate

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#1 Gabe Phillips

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Posted 30 June 2015 - 07:27 PM

Can anyone explain the advantages and disadvantages of shooting in 50i vs 25p. I have a C100 which offers both and am trying to get the best footage out of the camera, and need some advice.

 

Regards 

Gabe 


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#2 David Mullen ASC

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Posted 30 June 2015 - 08:30 PM

It's just a look thing - 50i (usually with no shutter, i.e. 1/50th shutter time) is associated with live events, news, reality programming, whereas 25P (usually with a 1/50th shutter time, i.e. closed 50% of the time) is associated with the film look, and often live events shot at 24P or 25P looked like taped events, like they happened in the immediate past and are being reshown.  It's mainly just a combination of the super-smooth liquid motion of 50i versus the stuttery, strobey motion of lower frame rates that contribute to this perception.  The other thing is that interlaced-scan photography has a certain sawtoothed edge to moving objects since the object has moved between and during the two sequential fields that are combined into a frame.

 

Today, you generally would not chose 50i for material that was traditionally shot on film, such as narrative fiction, though soap operas are technically narrative fiction but were shot interlaced-scan for decades, and you'd generally chose 50i for things like sporting events or live concerts, or the news, but even there, you have examples in history of sporting events or concerts shot on film (such as NFL Films presentations or many Olympic documentaries) and today, I've seen reality TV programming shot both ways, the ones aspiring to a certain "classical" film look will chose 25P over 50i.

 

Now it is possible that the settings in your camera are also asking if you want to record 25P capture as 50i instead of as 25P, which is a separate issue from actually capturing the scene at 50i versus 25P.  You may be delivering a TV project that has to be finished at 1080/50i, for example, even though a 25P look is desired.  Keep in mind that there is no 25P/1080 HDTV broadcast standard, so a project finished as 25P/1080 could get released on blu-ray or the internet as 25P/1080 but a 50i/1080 version would have to be created for broadcast.


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#3 Tyler Purcell

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Posted 01 July 2015 - 02:26 AM

Anytime "i" is used after a frame rate, it refers to "interlaced". So 50i is an interlaced version of 25 FPS. So 25P is the progressive version.

Broadcast TV is interlaced, that's how they can fit so much data down the pipe and make it work. One field contains half the data and the other field contains the other half. This creates an image on your TV at 50 fields per second or 50i. This is an old frame rate which was generated by the frequency of electricity, 50hz in Europe and 60hz in America (50i/60i)

Interlaced material has many benefits, it's easier to do post production slow mo where two fields are blurred together. It's generally a smaller file size because there is less data. The disadvantages are also pretty big, as David said, the scan lines can cause some jagged edges on motion shots.

So broadcast generally uses interlaced and everything else is usually progressive.
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#4 Gabe Phillips

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Posted 01 July 2015 - 09:42 AM

Thank you to both of you! That has cleared all my questions about the two formats up completely

 

Thanks again 

Gabe 

It's just a look thing - 50i (usually with no shutter, i.e. 1/50th shutter time) is associated with live events, news, reality programming, whereas 25P (usually with a 1/50th shutter time, i.e. closed 50% of the time) is associated with the film look, and often live events shot at 24P or 25P looked like taped events, like they happened in the immediate past and are being reshown.  It's mainly just a combination of the super-smooth liquid motion of 50i versus the stuttery, strobey motion of lower frame rates that contribute to this perception.  The other thing is that interlaced-scan photography has a certain sawtoothed edge to moving objects since the object has moved between and during the two sequential fields that are combined into a frame.

 

Today, you generally would not chose 50i for material that was traditionally shot on film, such as narrative fiction, though soap operas are technically narrative fiction but were shot interlaced-scan for decades, and you'd generally chose 50i for things like sporting events or live concerts, or the news, but even there, you have examples in history of sporting events or concerts shot on film (such as NFL Films presentations or many Olympic documentaries) and today, I've seen reality TV programming shot both ways, the ones aspiring to a certain "classical" film look will chose 25P over 50i.

 

Now it is possible that the settings in your camera are also asking if you want to record 25P capture as 50i instead of as 25P, which is a separate issue from actually capturing the scene at 50i versus 25P.  You may be delivering a TV project that has to be finished at 1080/50i, for example, even though a 25P look is desired.  Keep in mind that there is no 25P/1080 HDTV broadcast standard, so a project finished as 25P/1080 could get released on blu-ray or the internet as 25P/1080 but a 50i/1080 version would have to be created for broadcast.

 

Anytime "i" is used after a frame rate, it refers to "interlaced". So 50i is an interlaced version of 25 FPS. So 25P is the progressive version.

Broadcast TV is interlaced, that's how they can fit so much data down the pipe and make it work. One field contains half the data and the other field contains the other half. This creates an image on your TV at 50 fields per second or 50i. This is an old frame rate which was generated by the frequency of electricity, 50hz in Europe and 60hz in America (50i/60i)

Interlaced material has many benefits, it's easier to do post production slow mo where two fields are blurred together. It's generally a smaller file size because there is less data. The disadvantages are also pretty big, as David said, the scan lines can cause some jagged edges on motion shots.

So broadcast generally uses interlaced and everything else is usually progressive.


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