Low Light EX1 Overcrank

Elton

Elton

Veteran
Extremely basic shot. My friend Chris let me grab the camera and just chase the kids and see how the slowmo turned out.

Shot at an outdoor mall with only the available light. (dim christmas tree lights mostly) It was 60p for 24 playback and at a 1/120 shutter. No CC--footage was transcoded to ProRes and then h264. Apologies for the fairly heavy compression but file size needed to be kept to a minimum.

Right click, save: http://homepage.mac.com/mrbarlowelton/.cv/mrbarlowelton/Sites/.Public/KidsLoLightSlow.mov-zip.zip
 
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Hey Elton, I haven't checked the video yet (downloading) but what do you think of the EX1 so far? I'm very curious about this camera.
 
Thanks for the file, Elton. I can only imagine how good the source file must be before h264 encoding. The EX1 has my attention. What gain setting, if any, in dB?
 
rawfa said:
Hey Elton, I haven't checked the video yet (downloading) but what do you think of the EX1 so far? I'm very curious about this camera.
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Hey rawfa,

The EX1 is a really good performer. It was amazing to be shooting at that shutter speed in low light and still have decent exposure. Good latitude, clean blacks and the resolution is great. XDCAM HQ codec is solid too.
 
Christopher Barry said:
Thanks for the file, Elton. I can only imagine how good the source file must be before h264 encoding.
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The original source is great, even when converted to ProRes. It's impressive that it does good 1080p, but I'm actually more impressed with the 720 mode. Very low compression and really clean with 1-60 fps available.
 
Elton,

0dB, wow! And yes, at 1/120, I was surprised when reading the thread initially. No rolling shutter issues, and such a shutter speed would assist in preventing that in this instance.

Any chance of a few uncompressed still frames from the shoot? I would like to see how robust the image is to grade via a Curves filter. Thanks
 
Elton said:
The original source is great, even when converted to ProRes. It's impressive that it does good 1080p, but I'm actually more impressed with the 720 mode. Very low compression and really clean with 1-60 fps available.
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Elton, I was reading some of the comments by yourself and others at DVinfo and if I understand correctly, shooting EX1 1080p or 720p, the same data rate of 35megabits VBR in HQ mode is applied, thus you should get cleaner footage from 720p as the EX1 is applying the same compression data rate over less pixels, which should result in less compression. Is that a correct analogy and apply to your statement above?
 
Christopher Barry said:
and such a shutter speed would assist in preventing that in this instance.
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Shutter speed has nothing to do with rolling shutter. A faster frame rate would help assist in preventing a rolling shutter effect (as in, rolling shutter is more prevalent at slower frame rates than at faster frame rates) but the shutter speed is irrelevant. You'll get as much rolling shutter at 1/2000th as you will at 1/24th.
 
Christopher Barry said:
Elton, I was reading some of the comments by yourself and others at DVinfo and if I understand correctly, shooting EX1 1080p or 720p, the same data rate of 35megabits VBR in HQ mode is applied, thus you should get cleaner footage from 720p as the EX1 is applying the same compression data rate over less pixels, which should result in less compression. Is that a correct analogy and apply to your statement above?
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Yes, that's correct. 720 24p has more than twice the bandwidth per pixel than 1080 24p.
 
This 720p vs 1080p compression analysis should make for some interesting tests in the future, especially low light shoots. Even though the EX1 is proving to have a very sensitive CMOS, getting the best out of the EX1's codec in HQ mode will be an interesting exercise to learn by experimenting/testing.
 
The 1080P stuff looks really good - so much detail, but I must admit the 720P stuff looks magical off this camera, very clean looking.
 
It sure does, Steven. Interested to see how 720p compares to 1080p for shadow detail, and sub 40 IRE range setups. Are you seeing any benefits, Steven?
 
Barry_Green said:
Shutter speed has nothing to do with rolling shutter. A faster frame rate would help assist in preventing a rolling shutter effect (as in, rolling shutter is more prevalent at slower frame rates than at faster frame rates) but the shutter speed is irrelevant. You'll get as much rolling shutter at 1/2000th as you will at 1/24th.
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This seems counter-intuitive... can you explain a bit more? That is, how exactly the rolling shutter is implemented that would make the effects insensitive to shutter speed?

It seems to me that at a 1/2000 shutter speed, all data is read of the sensor in 1/2000th of a second, and that would result in less motion (and less rolling shutter distortion) than if the data is read off at, say, 1/60th for the same camera/subject motion. What you are saying seems to imply that the "shutter" sweeps down the image at a fixed rate for a given frame rate, with each pixel (or line?) sequentially accumulating light for a time period determined by the shutter speed?

I guess the question is, on a CMOS sensor, how are the start and end of light accumulation triggered for each pixel; how is the data scanned off the chip, and how do the two processes interact?

I'm of course off to research this... but if you have a clear explanation handy, please let us know...
 
Interesting - it seems the electronic rolling shutter is an exact analogue of the mechanical rolling shutter - that is, there are two sweeps through the image; one to reset each pixel and one to read out the accumulated voltage. The time (seemingly, measured in rows at a fixed time per row) determines the shutter speed - just like the gap in a mechanical fixed-speed rolling shutter. That is, the time between when the reset sweep and when the read sweep are started determine the exposure time, while the actual sweep speed remains constant.

However, in a variable frame rate camera, it seems that the time to sweep through each frame is certainly variable; one might surmise that it COULD be possible to sweep the image faster at a higher shutter speed. Perhaps this is the kind of thing RED (and perhaps Sony) are doing to minimize the rolling shutter effects...
 
ullanta said:
This seems counter-intuitive... can you explain a bit more? That is, how exactly the rolling shutter is implemented that would make the effects insensitive to shutter speed?
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The rate that the rolling shutter "rolls" down the frame is set by the frame rate, not the shutter speed. The rate that the rolling shutter exposes each line is set by the shutter speed. The shutter will sweep the frame in 1/24th of a second, or 1/30th, or 1/60th depending on your frame rate and regardless of shutter speed.

What you are saying seems to imply that the "shutter" sweeps down the image at a fixed rate for a given frame rate, with each pixel (or line?) sequentially accumulating light for a time period determined by the shutter speed?
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That's my understanding of it, yes.

Russ Andersson talks about it more here:
http://cybermessageboard.fatcow.com...start=15&sid=49a7b8cfcd77cb7dcd735c4b175c1802
 
ullanta said:
Interesting - it seems the electronic rolling shutter is an exact analogue of the mechanical rolling shutter - that is, there are two sweeps through the image; one to reset each pixel and one to read out the accumulated voltage. The time (seemingly, measured in rows at a fixed time per row) determines the shutter speed - just like the gap in a mechanical fixed-speed rolling shutter. That is, the time between when the reset sweep and when the read sweep are started determine the exposure time, while the actual sweep speed remains constant.
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Yes, but with a MASSIVE difference -- the mechanical shutter exposes the entire frame for a large part of the exposure time. The CMOS rolling shutter doesn't, it only exposes a line at a time. Huge difference. A film camera will have global exposure for almost the entire shutter time, and thus will have the signature motion blur we come to expect from a film camera. And the entire frame is exposed all at once for most of the exposure time. Even the top and bottom of the frame will be exposed simultaneously on a rolling mechanical shutter for some amount of time.

A CMOS rolling shutter won't have that, it'll have different exposure completely. The top will be started and finished long before the bottom even starts. Totally different process, and those who say a rolling CMOS shutter is "just like film" either have no idea what they're talking about, or ... well, can't really think of an "or" to that! :) It's possible to get a little bit of leaning out of a film camera if you pan very quickly, but nothing like the "skool" video would ever happen on a film camera.

However, in a variable frame rate camera, it seems that the time to sweep through each frame is certainly variable; one might surmise that it COULD be possible to sweep the image faster at a higher shutter speed. Perhaps this is the kind of thing RED (and perhaps Sony) are doing to minimize the rolling shutter effects...
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I talked to the guys from Thomson about how they were dealing with it, and basically they run the camera at double speed internally. So when set to shoot 60i, internally it's actually running at 120fps and they just discard every other frame. By cranking up the frame rate, that inherently speeds up the "sweep" rate. I don't know how Red is trying to address the issue. I guess it's possible Sony might do something similar, who knows... maybe they employ double-speed sweeping up to 30fps (i.e., internally running at 48fps when recording 24p, and discarding every other frame) but once they hit 30fps or more, dropping to no double-sampling? Or maybe internally the thing's running at massive speeds, 120fps or 240fps, and thus using only one out of every two or four frames, but using that cranked up frame rate to get a faster sweep rate?

If so, though, you'd expect a limit on exposure time based on the frame rate... if they were running 120fps internally to generate 60fps, you should theoretically not be able to set a shutter speed slower than 1/120th. At 120fps the "sweep rate" must be completed in 1/120th of a second, so you couldn't go exposing 60p at 1/60th in that scenario. So, question for EX users: can you set a shutter speed of 1/60th when shooting 720/60p? If so, that would seem to imply that they're not using a doubled (or more) internal frame rate.

Wouldn't it also seem to mean that the rolling shutter lean/wobble would be a lot more noticeable at slower frame rates... If you're running 2 fps at 1/2 second, the sweep would have to be no faster than 1/2 second, yes? Therefore massive leaning should happen, should it not? Of course, much of the lean would be hidden under the blur of a 1/2-second exposure too.
 
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