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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Another CMOS question

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WILLIAM SPENCE

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I know that there is a mysterium upgrade happening in the future, and it got me to thinking about CMOS again. I know that right now it is prohibitively expensive to build a global shutter CMOS sensor. But I am wondering if you were to decrease the scan time short enough on current CMOS technology, if you would be able to essentially minimize rolling shutter problems like scew/partial exposure/wobble to the point that a global shutter would not be necessary? Any thoughts, or are there more effective ways than scan-speed to improve rolling shutter problems?
 
Unfortunately, I don't even own a RED yet, so don't know how different builds have affected things. But from following this forum and viewing lots of footage, it seems clear to me that RED has a better handle on rolling shutter issues than Sony and Canon. So I figured with the high level of expertise available here, it would be a good place to pose the question. I know that Sony has been doing some sort of column summation, but I don't know if that is a more effective approach than simply making the scan time as small as possible - ?
 
From our tests Red is doing very well in this field – it's not free of RS effects, but it's quite a bit faster than Sony's EX-1 ( which is showing exactly the same degree of RS as a cheap, but good Canon HV20 ).
We are currently doing excessive testing for 3D motion tracking with different cameras. I'll report our results.

Regards,

Uli
 
Nomad, that sounds like an exciting test. Please do report on that test as i am sure that many here would like to hear the results. Any other thoughts on how to improve RS effects without the cost of a global shutter? I figured with the new Mysterium X approaching, that would be one of the issues at the top of RED's priority list since they already have the finest image available(IMHO). I'm just curious if extremely fast scan times alone could improve the issue, or if it is being approached in the industry in some other engineeringly genious way :)
 
In situations involving a lot of movement, RS may be noticeable. For example sports. In the current football series in Europe, the dominant broadcast camera is Sony HDC-3300. Sony uses 3-CCDs with 2/3" lens.

Dalsa Origin 4K and Sony F35 cameras have no RS. Arri D21 claims to have no RS. But look at their price.

For most scenes in movies, RED can be used without any noticeable RS. Ketch Rossi has made a feature length movie with RED. He has no complaints (only praises) for RED.

You have to look at the price advantage of RED. The quality you get with RED for $17K is amazing. (with lens, monitor, etc. < 50K).

P.S.: Comparing RED to consumer cameras under $6K, like EX1 and HV20 is unfair. RED should be comapred to F35, D21, Origin 4K, etc.
 
Well, the Dalsa and the Arri-D21 have mechanical spinning mirror shutters, and the F35/23 uses CCD's I believe (as does the Dalsa).

Besides the RED, the other CMOS cine cameras with no mechanical shutters are the Phantom and the SI-2K.
 
I remember iBloom and some others discussing the possibility of an 'add-on' mechanical shutter in front of the actual lens... I think. Bit fuzzy on the details of how this would be effective in tackling the problem but that's the only example I can recall of "engineeringly ingenious" solutions.
 
I am certainly not comparing the RED to Canon or Sony, the EX1 and HV20 are not in REDs class. But I have read enough to believe that it may not be the best idea to shoot RED at a model catwalk with a million flashes going off - at least not yet. I just thought it might be interesting to open a technical discussion on how to improve the RS situation from a technology standpoint. During a pan, if it is fast enough, skew is induced because of the time it takes for the chip to be scanned from top to bottom. My thoughts are that if you could really increase the scan speed of the chip, that rolling shutter issues would just disappear and the expense of a global shutter would become unnecessary. What I do not know is if there is a bottleneck or physical limitation that would make the scan speeds necessary to accomplish this to be unattainable. But I do believe that the first chip manufacturer that comes up with a solution is going to have a big foot in the door and sell lots of them until the other companies can catch up. I personally am hoping that it will be RED. I am curious as to if anyone has any other theories such as column summation or other ideas on how to improve on the problem yet keep it affordable - ie keep global shutter unnecessary.
 
Sony has developed a 35mm CMOS 24x36mm 24.81 megapixel imaging sensor.
It output all pixels at 6.3 fps with lower noise. This is achieved by “Column-Parallel A/D Conversion Technique” whereby each column of photosites is given its own Analogue to Digital Converter.

So far this is the best CMOS chip in this segment. It will be used in SLR cameras. If this chip is used without a shutter in a videocamera, the RS problem will be reduced but not eliminated.

Sony and Panasonic have half a century of R&D and they use CCDs for a reason.
Origin and ARRI have quietly spent years researching this stuff before using a shutter solution.
This is one of the resons for their higher price tag.

When a shutter solution is used, the price of the camera will be higher than $17K.
For $17K, you have to accept some compromises.
You may never get such a low price from Sony or Pani or anyone else. Because they all sell through middlemen.
Sony executive told me that the Sony factory gets only 25% or less of the suggested retail price.
The rest is all eaten up by middlemen.
So, to sell for $17K, sony has to produce it for $4.25K or less.

'no overhead' is the reason why Jim can give you a camera this cheap.
In the future, I hope, Jim might produce a more expensive camera with a shutter solution.
 
I'm kinda confused about this whole mechanical shutter with a CMOS sensor thing... how exactly would that help the rolling shutter issue?

The issue is that a CMOS sensor cannot capture the light over the whole surface at one time the way a CCD can. How would covering up the CMOS sensor, partially or completely, help in this situation? Maybe it's obvious but it's not jumping out at me.

Thanks - Mike.
 
VMax said:
The issue is that a CMOS sensor cannot capture the light over the whole surface at one time the way a CCD can.
Click to expand...

Actually this is not the problem.
The CMOS can accumulate ligt across the whole sensor, its the readout and reset of the captured light in the photosites/gates that has to happen in a serial process, one line at a time. This is why a mechanical shutter will fix the problem, by covering the sensor while this part of the cycle is happening.
 
Oh ok. Thanks Anders.

So basically, the CMOS chip stores the charge created by the light hitting it so even if it goes into total darkness, it still has this charge. Is that correct? So if any further light hits it, it changes this charge as time passes so that the image is changing before it can be read, is that it? Seems to make sense to me now. So a CCD must somehow freeze the charge at each photosite so it doesn't change over time, regardless of further exposure to light, until it is read. Hmm... I think I get it now! (?)
 
VMax, I was a bit confused by the mechanical shutter and what Anders said as well. But if your deduction that the mechanical shutter blocks the light and the charge is held and read off line by line during the time that the shutter is blocking the light, then this makes perfect sense. Which raises a few more questions regarding a mechanical shutter.

- How complicated is it to make a mechanical shutter that will do this properly? It would seem to be a simple solution, but then again things are rarely as simple as they seem.
- What are the limiting factors that a mechanical shutter introduces? Motor noise? Lowered frame rates? Shorter battery life? Higher failure incidences requiring maintanence?
- Would this be a cheap solution that could eliminate rolling shutter issues for manufacturers, or are there other solutions that make better sense?
 
There is a bit of mis-information here. A mechanical shutter does EXACTLY what a rolling shutter does. It wipes the image from top to bottom (or side to side in some cameras). Just as a read-reset sensor does. Covering the part of a sensor that has already been read does nothing more than the sensor does itself. There is skew with a mechanical shutter just as there is with a read-reset sensor. The only difference is the time it takes to "wipe" the image plane vs. read-reset the sensor. In the past, the time has been much longer to read-reset (the more time it takes the more of a problem it creates). Those days are coming to an end. A mechanical shutter has much less advantage than people give it credit for... especially as CMOS sensor read-reset times shrink, and eventually are quicker than mechanical shutters.

Most people think RED footage has a "filmic" look. Much of that is due to the high, unsharpened resolution... but a lot of it is due to the "feel" of a fast read-reset sensor.

When we 1st announced this camera, we were told by the "top dogs" that it was mandatory for us to include a mechanical shutter. We haven't been asked for that feature by the feature film, ASC guys in a long time. I wonder if they aren't now used to seeing a "bright" image on an LCD instead of a "dark" image through an eyepiece in low light?

Jim
 
I am not sure I underatand.
Many has pointed out the RS in RED.
F35, Origin 4K, D21 etc. claim to have no RS.
Are you saying, in the future, RED will have a solution for RS without a mechanical shutter ?

Sony claims to have the best 35 mm CMOS sensor at this time. Are you planning to use Sony sensor in RED?
 
Not sure what part of this you don't understand...

The only "problem" with a rolling shutter is a long read-reset time. History will not look kind on early CMOS sensors because this time was too long. We have shortened the read-reset time considerably just in the last year. Next generation sensors (Epic, Scarlet and RED ONE upgrade) will equal that of a mechanical shutter. After that, they will be faster.

Try to wipe your mind of preconceived notions...

Jim
 
My last rolling shutter comment for the night. A rolling shutter (with correct read-reset times) is a GOOD thing... not a bad thing. It accurately emulates a mechanical shutter if the wipe times are similar. We PREFER the look to a global shutter.

Jim
 
Hmm... really interesting Jim. So, while I get what Anders was saying and I'm sure he's right about that, it seems my initial intuition that the mechanical shutter would offer little advantage with a CMOS sensor was not far off. In any case, an SLR with a focal plane shutter has always had the same issue yet no-one seems to consider it a problem. I cannot see it as a big issue with a motion picture camera either if you're trying for a filmic look. Even a fast paced scene like a car chase is going to have the camera following the action. Only the background will be at risk from rolling shutter artifacting and that will be motion-blurred anyway. If you're shaking the camera so much your "hero" character - vehicle or human - is warping, it's definitely not going to look filmic.

The only issue I see as insolvable with a RS sensor is flash photography in the scene which can be of extremely short duration; perhaps as short as a 30,000th of a second. No RS sensor can protect against that, at least not to my knowledge. But all photographic equipment has limitations you have to be aware of. Red is of course no exception. You just have to work around these issues as you would with a film camera. (With a film camera, you may miss a flash altogether and have to add them in post if that's what you're trying to capture.) What Red offers far outweighs these issues. If you bear them in mind, as you have to for any other capture system - film or otherwise - Red will do an excellent job, way beyond its pricepoint. An industry shaker indeed.

Regards - Mike.
 
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