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#1 Thomas Tamura

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Posted 31 October 2006 - 10:09 PM

I've done several test shots at different shutter speeds with the Z1 and I am seeing some increased resolution, but is it all in my mind? What exactly does this function do, because it's not changing the frame rate (which shutter speed should be linked to), and it's still giving me footage at 30 FPS. With the GOP MPEG compression I don't see how it could be writing more key frames either. Any one care to discuss this with me. I've used it a couple of times more for controlling exposure then doing in camera FX.
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#2 Matt Sandstrom

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Posted 02 November 2006 - 08:01 PM

well, as the name indicates it changes the shutter speed, which is how long each frame is exposed. the frame rate indicates how many frames are shot per second but says nothing about how long each is exposed. the reason you see more res is probably because there's less motion blur. this will also create more sharp detail, which means the electronic sharpness is applied more, making it look even sharper even though resolution doesn't increase.

/matt
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#3 Thomas Tamura

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Posted 02 November 2006 - 11:08 PM

well, as the name indicates it changes the shutter speed, which is how long each frame is exposed. the frame rate indicates how many frames are shot per second but says nothing about how long each is exposed.

/matt



Matt,

thanks for the reply, and I see what you're saying. In film cameras frame rate and shutter speed are one and the same. As you know 24 FPS is 1/48 of a sec shutter speed. When you lower the shutter speed (and create longer exposure time) you get a similar result to a film camera shooting at a slower shuttter speed, but not when you go faster speed. I was hoping some one could provide some insight into the more technical aspect of the compression. I guess I should have been more clear on that. Sorry.
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#4 Matt Sandstrom

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Posted 03 November 2006 - 01:30 PM

In film cameras frame rate and shutter speed are one and the same. As you know 24 FPS is 1/48 of a sec shutter speed.

not really, that's assuming you got a 180 degree shutter. many cameras have 150 degree shutter, which results in a shutter speed of 1/60, and many have variable shutters where you can change the angle and thus the shutter speed to whatever you want, as fast as you like and dows to almost 1/24 after which you'll start seeing the streaks from the pulldown.

When you lower the shutter speed

oh, you mean when you go slower than the frame rate? as a matter of fact that *does* change the frame rate of the video, it's just that frames are duplicated. there's no other technical possibility. variable frame rate video and hd cameras fo the same, and then you remove the duplicates in post.

i just realised that there's actually the possibility for a camera to create full frame rate long exposure but that would require a ccd which you can start reading from again when the previous frames were still being read. or it could be done all in the dsp, using frame blending, but that would create artifacts. this is definitely something i need to research the next time i have one of those cameras...

/matt
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#5 Thomas Tamura

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Posted 04 November 2006 - 03:22 AM

Yes -- assuming 180 degree shutter -- that's great that you know so much about film cameras, but you haven't answered my question. I didn't start this thread for a intro to FILM lesson. Clearly the camera is duplicating frames to approximate what a longer exposure time would be -- so what is it doing when the shutter speed is increased -- compression wise; how does it affect the long-GOP. It's obviously not throwing out frames? It's not writing more data either now is it? so what is it doing to the structure of the MPEG-2 files? Thanks for trying, but I don't think you know
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#6 Tim J Durham

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Posted 04 November 2006 - 08:47 AM

Yes -- assuming 180 degree shutter -- that's great that you know so much about film cameras, but you haven't answered my question. I didn't start this thread for a intro to FILM lesson. Clearly the camera is duplicating frames to approximate what a longer exposure time would be -- so what is it doing when the shutter speed is increased -- compression wise; how does it affect the long-GOP. It's obviously not throwing out frames? It's not writing more data either now is it? so what is it doing to the structure of the MPEG-2 files? Thanks for trying, but I don't think you know


It's hard to tell exactly what you're after. You started with a series of wrong assumptions and Matt tried to dig you out from under them. Now perhaps you should change your tone and start over.
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#7 Matt Sandstrom

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Posted 05 November 2006 - 09:59 AM

Thanks for trying, but I don't think you know

of course i do. it compresses this stream just as it would any other stream. the recorder part of the camera doesn't care what the camera part is feeding to it. it's just a sequence of frames either way. no frames added, none dropped, no change in the gop. this is so obvious i'm sorry i didn't realize it was a question.

/matt
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#8 Thomas Tamura

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Posted 06 November 2006 - 03:06 AM

the recorder part of the camera doesn't care what the camera part is feeding to it. it's just a sequence of frames either way. no frames added, none dropped, no change in the gop.

compression wise; how does it affect the long-GOP. It's obviously not throwing out frames? It's not writing more data either


what is it doing when the shutter speed is increased


I was hoping some one could provide some insight into the more technical aspect of the compression. I guess I should have been more clear on that.


What exactly does this function do


this is so obvious i'm sorry i didn't realize it was a question.

It's hard to tell exactly what you're after.



/matt

Thanks for the help.
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#9 Yecid Benavides Jr.

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Posted 12 November 2006 - 05:28 PM

I hope I´m not too late, but it just seems to me, Thomas, that you don´t understand what the shutter speed is. It has nothing to do whatsoever with the compression; it doesn't affect your GOP's or any of that. All it is is how long (in fractions of a second) the camera opens THE SHUTTER so light can come in. Just reinforcing what Matt said, it may "look" to you like the resolution is getting better only cuz you're capturing a more frozen image as you go up in your shutter speed. Basically if you shoot a football in mid air with a very low shutter speed, your frames will look have a brown streak going through them, whereas if you shoot the same ball at a high shutter speed each frame will look like the ball is not even moving (commonly referred to as a frozen image). That's all... no resolution change...

Hope it clears things up,

Yecid (all the way from Bolivia) Jr.
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