"Rolling Shutter" Skew Tests and Grabs
 

I put the EX1 on a motion control head to try to quantify the amount of skew that is created by the "rolling shutter" on the EX1. (can we start calling it a "scanning shutter" instead?).

A chart with vertical bars was placed in front of the camera (which was at full tele to minimize distortion) the Kuper motion control head was programmed to pan, at a linear speed, precisely one bar per frame of video. I was only able to test 30p, and I would like to test other speeds, but my sense is that it would all be proportional.

What I concluded is that the skew is the same for all shutter settings (I tested 1/2000, 1/250 and 1/60) and that the shutter scans at twice the rate of the camera - that is, if the camera is set to 30fps, the shutter scan takes 1/60 second from top to bottom. Higher shutter speeds are achieved by a "slit scan" of the sensor, similar to the curtain shutter of an old film SLR camera.

Here is how I arrived at that: Each bar on the chart is 110 pixels wide. So we can say that the EX1 is panning at 110 pixels per frame. The amount of skew from top to bottom is 55 pixels - half of 110, and hence half of the duration of the frame.

If you are curious about the equipment I used, go to www.general-lift.com for more info. There are pictures of the motion control head etc. They were kind enough to let me use their gear.

Here's what the grabs show:

No skew - static chart
Skew at 1/2000 (with graphic)
Skew at 1/250
Skew at 1/60

Eric that's some very good clean results, thank you.

If it moves that much horizontally then you know it will do the compress/expand effect vertically as well. I would have thought that would rule out shooting in a car for example.

I quite disappointed with the results, as indications had suggested (along with sonys marketing) that it would be a lot better than this. Seems like quite a slow read out to me too (1/60th second!)

thanks
paul

Eric,
Thanks for your careful testing and hard work.

Can you post any video so we can see how fast these pans are in real motion? It's great to know that shutter has no affect on the skew , but I want to know when my pans or motion will begin to be affected.

Perhap[s tghat was not part of your testing though.

very interesting. this is a very well done test. it would be more interesting to see a comparison between different formats since the fact that the speed of a cmos sensor's electronic rolling shutter does not affect the the readout rate or resulting skew has been documented. with various formats, however, depending on how the various frame sizes and frame rates are arrived at in terms of sensor clocking, blanking, etc. there could be a significant difference in the skew effect.

Noah - good point. I will have to try 720 - knowing what I know now I could easily to it on my fluid head, analyzing two successive frames, and won't need to use the moco.

My guess is that it will be the same, but it's worth a try.

Leonard - I will post a quicktime of the pan - I'm just sorting out with Chris H. why I can't upload a small mov file.

it seems that it would be difficult to guarantee that the pan speed will be constant each time without motion control. perhaps there is some object that can move across the screen a known speed? without knowing precisely the speed of the pan/movement it would be hard to be sure of the results especially if the differences are not large in relation to the size of the video frame.

Eric, thanks for this test.
Can you give us an idea if it's close to the RED ONE numbers below for skew based an image moving across the sensor at a consant speed.

Jim Arthurs' tests show with the RED ONE 18 frames will skew 3% of the 4K width.

This means if shooting at 4K 24P, a constant speed pan (good luck ;) ) from one edge to the other takes 750ms, it can cause 3% skew on the 4K images.


Jim also mentioned if the pan speed was reduced to 3 seconds, there's virtually no visable skew.

Eric, if you still have the test stuff around, can you do the same thing for tilt (up/down) movement. I'd like to see this measure affect too.

So Eric,

Is it safe to assume that since you were long on the lens and in a practical way took the arc out of the equation, we should assume the same results for a dolly - or tracking move? If all other factors are relative - frame, focal length, distance from object etc.

vince

The point of going full tele was to take the arc and the rectilinear lens distortion out of the equation as much as possible.

Even with the arc, the measurements were taken near the center of the image, and from the same part of frame, so the arc is not significant.

Skew should be considered a 2D phenomenon that happens on the flat surface of the sensor - is doesn't matter how you arrive at the motion that's projected on the chip - it could be dolling, panning, zooming, subject motion or some combination thereof. But if there's something that should appear vertical moving across the chip horizontally it will be skewed.

Likewise, as I'm sure is obvious, if you are panning or dollying with a moving subject, the subject will not be skewed and the background will.

Red Comparison
 

So I looked at this footage shot by Jim Arthurs on the RED forums and analyzed two successive frames - 170 and 171.

http://www.reduser.net/forum/showpos...98&postcount=1

(It's the first link)

The movie is low res (800x450) but the proportions are correct. The pan speed there is 66 pixels/frame and the skew amount is 22 pixels.

So in this example, the RED shutter scans the sensor at 1/3 the frame interval, which is better than the EX1 which scans at 1/2 the frame interval.

I'm checking with Jim to make sure that this image is downresed from the full chip rather than cropped. Cropping would reduce the amount of skew in for the part of the sensor that's used.

I hope everyone will forgive a very novice question (I've never heard of skewing, so this is all educational for me):
Is Skewing an inherent trait to all DV cameras? or CMOS only?
For example, I've not noticed it in my Canon XL-H1, or my Sony Z1u. Which is to say, I've never looked for it and rarely do fast pans and the trait may very well exist.
I look at the examples and am somewhat awed.

It's CMOS only - it uses a 'rolling shutter' (or 'scanning shutter' ;D ), sampling the image from top to bottom. This causes distortion if the image has moved between when the top and the bottom have been sampled. CCD cameras such as the Z1 (which I own as well) do not exhibit this behavior as they scan the whole image at the same time.

Hope this helps!

Carl

It does. Thanks Carl.
I was HOPING it was in all cameras of this nature - then I would say, "Engh, all cameras do it, so I'm OK with purchasing the EX1."
But since this is something inherent to CMOS, I have some weighing of priorities to consider.

Thanks very much.

Thank you so much Eric.

I'm interested in the 24P case. Is the scan speed still remained at 1/60 sec, or reduced to 1/48 sec. Would you please examine that?

Yes, I will. Give me a day or two.

What to do!
 

I got my EX back from Sony and the re alignment seems to have solved the vignette issue. But having read a fair amount about the rolling shutter effects I am considering an attempt to return my camera.

I primarily film action sports such as kitesurfing, surfing etc. My fear is that capturing this type of action it will be difficult to avoid quick panning movements or high speed images flying through the frame.

I was shooting some paddle surfing this morning and in one shot I quickly panned from one rider to another. The building in the background skewed so far over it was truly alarming.

I did one test where I locked off a shot directly across the street to see how the cars looked as they drove through the frame. At 35 mph the skew was acceptable but often I am shooting faster objects coming past the camera.

There are many things I love about the EX1. Larger chips, DOF, image quality, lens control, low light capabilities and image control.

I am moving up from the PD 170 CCD world and have waited a long time to make the jump. I am concerned with what I am seeing. I was not interested in HVX 200 but I am uncertain of where to turn.

Any advice is greatly appreciated

This is alarming.

The EX looks like a great value except for this rolling shutter behavior.

The next option imho is the HPX-500 or the XDCAM 335/350.

But they will bring the price to the $20,000 range.

Makes one think, "maybe a skewed building here and there is not so bad"...

>The building in the background skewed so far over it was truly alarming.

Rapid changes of direction will be worse, if you're just panning in one direction the skew is perhaps acceptable and the public won't notice but if the skew changes direction then it leaps out as something wrong. And we haven't really touched on vertical squash and stretch.

Im glad that we're hearing and seeing some real world examples. I think the same will happen to Red as well (perhaps to a lesser degree) and maybe SI (the sensor can do 60fps as well which is probably the scanning speed limit). It's a case of how fast can the system read the sensor. On the EX i would imagine that 720 will be the same because the camera would scan everything and downsample? Or maybe it scans different lines to get the 720 image in which case it could scan faster (but loose some image quality advantages).

I've mentioned elsewhere that im quite disappointed with sony and their marketing hype. I remember statements being made about substantionally reducing this effect that simply aren't true. Which is a shame because if you look at sonys sensor side of the business they do have great cmos technology working at high speeds. So they do have the sensors and the knowhow but somewhere between the design and implementation things don't work as advertised.

There is a reason why sony mandate that pro and broadcast gear is CCD and consumer is CMOS. So perhaps this limitation in the EX is being driven more by marketing than tech.

We have some pilot/test stuff to shoot in the not too distant future, i may hire one to see for myself and compare to the other XDCAMs rather than just buy (because everything else is so attractive about it and i can get two for the price of something else)

cheers
paul

I've been reading a lot of things about the rolling shutter, some of them are valuable comments, scientific explanations, or well done tests like the one posted here by Eric. But there are also a lot of misinformation, people who fear this effect like if it was the devil, and the people who post comments having no idea at all of what they are talking about.

Well, I'll put my two cents here. From the tests of Eric, we can see that the scanning rate is double than the frame rate.

By scanning rate, I mean the time it takes for the CMOS sensors to scan one complete frame. This is the time difference between the moment the top line is read and the moment the bottom line is read, and it is what effectively causes the skewing effect we see on the image. Current CCD's don't show this effect because the whole image is stored in a memory when the integration time is complete, and then it is readed slowly, but every pixel of the image has started and has stopped storing light at the same time.

Eric has pointed out that the scanning rate is always the same no matter which shutter speed you use. I'll go further saying that this scanning rate is not neccesarily linked to the video frame rate you set on the camera. This means that the scanning rate can be the same no matter you set the camera at 30, 25 or 24 fps. Just think about the camera like a photographic camera, but taking several images by a second (that's where all started...). You have a clock that tells the camera when to capture a frame, or 'that pushes the trigger button'. This is the frame rate. So, in this test we saw that the scanning rate was double of the frame rate, that is, 1/60th of second at 30 fps, but if the scanning rate was the same 1/60th of second at 24 fps, the effect would be less noticeable. And this explains why the effect is less visible in the EX1 than in the Canon camera whose model number I can't remember and whose scanning rate was surely the same as the frame rate (1/30th of a second).

Notice that this is just what I have figured out from what I know about the technology, but it must be confirmed with new tests at the different frame rates. Tests that I will do as soon as my camera arrives, it had to be here this week, but it has been delayed and I have to way another two weeks! :(

When this technology evolve in the future, they surely will avoid the scanning shutter effects by increasing the scanning rate: if the complete image is scanned, say, at 1/300th of second, nobody will notice any skewing or the other weird effects... unless you use the camera to shot crash tests or other high speed things.

But I wan't to say that we also have to relativise this effect: in the great majority of the cases, we shot without shutter (I mean the standard shutter), so fast moving objects or camera movements will appear completely blurred like in the test frame in which the shutter was set to 1/60th. So... a test chart will show skewing, and we will notice it, or not, but in real life shots, I'm absolutely sure that people watching the footage will just be stunned with the high quality of the image, and nobody, except us, the fools with the cameras, will notice anything wrong with the images.

I don't mean it's not a problem at all: I see a problem when using fast shutter settings (slow shutter rates will blur the action) and very fast movements/moving objects. If you're going to shoot these kind of things, then the EX1 may not be the best camera for you... But for a lot of other kind of works, this camera is just perfect. It's just a matter of compromising: this camera achieves it's high performance thanks to it's new CMOS sensors, but that is just what causes its weakness, scanning shutter artifacts.

I'm becoming a pain in the neck, so I just wan't to say that I have seen this infamous effect in... my old Betacam camera! Yes, it's powered with Hyper HAD CCD's, and yes, what I'm saying will cause some discussion, but I will demonstrate that as soon as I can.

Yes, this has been around on the 2/3" CCD cameras; pan any Betacam too fast and you get the same skewing effect. Usually it's a near whip job before you start noticing, but it's there none the less.

Good News (and bad).
 

Thanks, David for that post.

I tested some other speeds, without using motion control, but just looking at two successive frames to determine the ratio of pan speed in pixels per frame versus skew amount in pixels.

1080 24p had a ratio of 2.66, implying a scan time of about 1/64 second

720 24p had a ratio of 2.25, implying a scan time of 1/54 second

720 60p had a ratio of 1.0, implying a scan time of 1/60 second

It seems like the EX1 keeps a (reasonably) consistent scan time, as David suggested rather than a proportional scan time. So the effect is less noticeable on a frame basis at 24p, but in real world situations I would guess the skew would be equally noticeable at all speeds.

I am not sure why the numbers are a bit funny - there may be a fixed component to the timing that I am not incorporating into the algebra that would make everything equal out.

Anyway, the test is easy to do and I'd love to see people confirm or refute these numbers.

Shoot a vertical target (which crosses top and bottom of frame) at 1/2000 shutter. Pan rapidly. Examine 2 adjacent frames (in Photoshop) and see how much the target has shifted in pixels. That's the pan rate in pixels per frame.

Now look at either frame alone and measure the the horizontal difference from top to bottom of the target. That's the skew amount.

Divide. That's the ratio.

thats interesting. so the readout rate may always be 60fps... it would make sense if the maximum readout of the sensor allows at most 1920x1080@60fps. all other framerates are probably achieved by blanking(?) and frame sizes achieved not at the sensor level, just in processing. I suppose unless it is an interlaced sensor, it would have to be able to do at least 1080@60 to come about 1080i video. this might mean the sensor is capable of shooting 60fps at 1080, maybe the DSP cant handle it? this is all speculation of course. at least it is good to know this. this should probably mean that the skew and wobble characteristics will be the same over time, when played back at the speed it was captured at. now for stuff high speed stuff thats getting slowed down, 1:1 readout ratio might be tough...

Eric, Thank you so much again. Thank you David.

Eric, May I understand that the scan speed is very close to the RED in 24P mode?

The RED, from only one measurment, seemed to do 1/72, which is a bit faster than the Ex1. But further tests are necessary. I need to check with Jim Arthurs and have him try a few speeds.

Anyone used an EX1 in a helicopter? With or without a gyro?

I'm sorry. I have to apologize, because I said a stupid thing. What I saw in my Betacam was an optical effect, probably due to the fact the viewfinder is a CRT. It can also be seen on a CRT monitor. The skew is an illusion produced because it's the CRT who generates the image as a "rolling shutter".

http://img405.imageshack.us/img405/8164/mov2000dg3.jpg

These are two consecutive fields of a weirdly fast pan, shot with a DXC-537AP dockable camera + PVV-1AP Betacam SP recorder. Shutter speed was set to 1/2000. As you can see, there's no skewing at all (but the standard Fujinon lens makes some pincushion distortion!).

[QUOTE=David Lorente;811241]I'm sorry. I have to apologize, because I said a stupid thing. What I saw in my Betacam was an optical effect, probably due to the fact the viewfinder is a CRT. It can also be seen on a CRT monitor. The skew is an illusion produced because it's the CRT who generates the image as a "rolling shutter".
QUOTE]

Well, you do have to bear in mind the overall system. It's only in recent years that there was any alternative to the CRT - LCDs and Plasmas can add their own little artifacts.

Hi Eric,

I've been studying your screen grabs showing the skew and doing a bit of math based on the image. IF I've calculated correctly, in your video any point on the chart should appear for 0.6 seconds or in other words, it first appears on the right side of the screen and 0.6 seconds later it falls off the left side of the screen after 0.6 seconds (18 frames). So this would be a VERY fast pan.

I've counted an offset of 53 pixels and an angle of 2.8 degrees.

All my numbers assume that the rolling shutter is 1/60th of a second from top to bottom.

It it's not too much trouble, could you please look at your footage frame by frame to see if any point on the chart appears for only 18 frames. At least that would tell me if my calculations are correct or not.

There is another way to measure the speed of the rolling shutter, but it takes some lab equipment, which I can borrow from the college where I work.


Sincerely,

Bob Diaz

Bob,

Yes, a given point on the chart takes about 18 frames to make it from the left to the right side at the speed I was panning on the motion control.

I'll try to post the footage. The forum was not letting me do so for some reason, which is what I only posted the stills.

I designed the pan so that each frame, the camera pans the width of one of the black or white bars.

Each bar is about 106 pixels wide - and 106x18 = 1908, or almost 1920.

Here's the movie.

It's highly compressed, but the timing is correct and the frames are intact.

It's the version with a 1/60 shutter.

Eric,

Thanks for the quick answer.

I did some thinking and I believe that it's possible to test the rolling shutter speed without test equipment.

If the EX-1 is set to a 1/120 or 1/60 shutter speed and you shoot a wall that is lit with a florescent light (powered by 60 Hz AC) and no other lighting, the wall should look evenly lit.

Now set the shutter speed to 1/2000 of a second and the wall will appear to have 2 horizontal bars (light --> dark --> light --> dark). The bars should appear to move slowly upward and wrap around. It should take a bit more than 8 seconds for one bar to move up off the top of the screen and appear on the bottom of the screen.

If the rolling shutter is always 1/60 (1/59.95) of a second, you should see the effect at 60p, 30p, and 24p on any still image.


WHY THIS WORKS:

Florescent lights flash at twice the AC Power Frequency. In the case of 60 Hz (60 Cycles Per Second), the lights flash at 120 Hz. This is because the AC power starts at zero volts, rises to the peak +voltage, drops back down to zero volts and reverses direction, rises to the peak -voltage in the reverse direction, and drops down to zero volts again. The light output of the florescent light follows the voltage at that moment.

When the shutter speed on the EX-1 is 1/2000 of a second, the rolling shutter is 32 scan lines high at 1080 and 21 (22 ?) scan lines high at 720. This slit moves down the CMOS image sensor in 1/60 of a second. As the florescent light flashes, the rolling shutter is moving down, so the current brightness of the light is recorded to the frame.

There is a slight mismatch to the frequency of the scan of the camera 59.95 Hz and the AC power 60 Hz. Thus it takes about 8.3 seconds for the 1/2 cycle to shift through the image.


50 Hz POWER:

I noticed that in the video, "South Bank" by Phil Bloom, that at 1:22 to 1:29, that the area to the right of the image, lit by a florescent light, seemed to have an odd flicker.

I know that the footage was shot at 25p, but I don't know what shutter speed Phil selected. I would think that a shutter speed of 1/50 of a second or 1/100 of a second would hide the flicker, so maybe the shutter speed was something else.

To me, it seems likely to me that the rolling shutter speed is 1/60 of a second even in 50p and 25p mode.


I don't have an EX-1 to work with yet, so posting a copy of the movie is very helpful. Thanks...


Sincerely,

Bob Diaz

Bob,

That all sounds right to me (I'll trust your math).

I did not test any of the "PAL" frame rates but it makes sense that the EX1 would scan at its fastest speed in all modes to minimize skew as much as possible.

As I am sure you know, PAL is 25 or 50 fps for real and not the horrible decimals we are stuck with (29.97 or 59.94) so PAL framerates won't "beat" with European line frequencies.

I've also noticed this flickering on Phil's video. Keep in mind that the shot we're talking about is slow motion, so the frame rate of the camera was not 25 fps. I think that in this particular shot the camera was overcranked to 60 fps.

If we divide the 100 Hz power cycle by 60 fps, we have a 5 to 3 relation. If I'm not wrong (again), this means it should take 3 frames for the flickering bars to repeat the same pattern, so it is quite annoying :(

I remember I saw a similar effect when I shoot in the projector room of a theater. They let me get in to shoot the film projector at work. I did some close-ups of the film passing by the gate, just in front of the shutter, and there was a noticeable flickering because of the film 24 fps rate vs PAL 25 fps, but, being a CCD camera, it was the whole image who flickered, going light and dark, instead of having rolling bars. If I had shot it with the EX1, I would have set the frame rate to 24, and the footage would have looked just nice.

So I think we would see similar problems with any kind of video camera, if we shoot something with a flicker rate close, but not matched, to the frame rate of the camera.

From my experience with the camera the flicker you mention only appears when the framerate is not equal to the AC Frequency. For instance if I overcrank to 25/60 I see horizontal banding, but at 25/50 there is none.


Does anyone remember those first leaked shots of the EX1 from the trade show? That effect was one of the first things we all noticed. Now that I can control it, I actually quite like the effect it has when it only happens on portions of the image such as a shop window. I used it at the end of this sequence...

http://www.vimeo.com/604159

regards

Paul.

If you narrow the shutter substantially you will see banding even if the frame rate matches the mains frequency. The bands won't move, but they will be there.

Of course, if you raise the shutter speed, those bars will appear. So... don't do it!

As I said before, I don't mean we should ignore the rolling shutter, of course it's going to cause problems under certain circumstances and it would be better if those CMOS sensors worked like the CCDs we are used to, but I just think there are workarounds to avoid these problems, and there are always things that can't be done with a particular technology, so nor CMOS neither CCD cameras are perfect. For example, with a photographic camera with curtains shutter, you can't use a flash gun at shutter speeds higher than the X sync speed, because you would get a partial exposure. A central shutter camera would solve this, but central shutters can't achieve speeds higher than 1/500th second. Nowadays, almost all pro SLRs feature curtain shutters, and only very specific brands (like Hasselblad) still produce central shutter cameras.

So, what we have to do is encourage Sony to raise the X sync speed of their CMOS sensors. This will also lead to higher overcranking speeds! I think a rolling shutter of 1/250 and a maximum overcrank of 125 fps would just be fine... :)

(Bob hits his head when he realizes that Phil's footage with the flicker was over cranked.) Boy, I was so busy looking at the flicker, I didn't look at the speed of the people walking.

Even with CCD cameras, if you use a very short shutter speed and florescent lights, you are going to have a flicker problem. In the areas with 60 Hz power and 59.94 Hz frame (or field) rate the flicker will be worse that 50 Hz power and 50 Hz frame rate.

For 50 Hz areas, there will be a VERY SMALL difference between the power frequency and the camera frequency. The difference could be 0.001% off, but over a long enough time it might show up. This would need to be a shot where one side is lit with regular light and the other side is lit with a florescent light.


AC Powered LED lights, like Christmas lights are going to pose a problem too. Most LEDs only work when the current is flowing in the forward direction and do not light when we try to pass the current in the reverse direction. Thus, they flash at 60 Hz USA, Canada, ... (50 Hz in Europe ...).

Indoor AC powered LED lighting is possible, but because of the high cost, we don't see it. Some of our traffic lights (or as we call them, "Stop Lights") in our area have switched to LEDs.

http://auto.howstuffworks.com/question178.htm

http://www.ledtronics.com/markets/traffic_index.htm

This could cause a flicker problem if the shutter speed of the camera is higher than the power frequency.


As for the battery powered LED lights, for units that dim the light, I believe that the frequency they are driven at is in the kHz range (1,000 Hz or higher). However, I have not had a chance to test this.

If I'm correct, battery powered LED lights won't pose a problem.

Bob Diaz

Very well said -- and I concur completely. Today I was updating the description of CMOS technology in my V1 book to include EXMOR technology. After a good deal of thought I think I understand EXMOR and how it differs from 3ClearVid. If you read what Sony writes, EXMOR uses a all digital output function based upon an A/D per column. Decreased noise is what Sony stresses is the benefit.

Fundamentally, EXMOR implements an on-chip digital output system that is time decoupled from the on-chip analog system. Chip read-out time (R) is decoupled from exposure time (T). Therefore, as exposure times increase longer than R, the rolling shutter artifact is reduced over an un-decoupled all-analog CMOS chip such as 3ClearVid.

The rolling shutter artifact is created at even moderate shutter speeds by most CMOS-based cameras because "scanning time" is equal to the exposure time. Thus, as CMOS rows are reset, from top-to-bottom, the row above the last reset row is read-out. The result is a one-row “slit” that travels down a “synchronous” CMOS chip. For example, at 24p where the shutter-speed has been set to 1/48th second, the “scan time” is 1/48th second and R (read-out time) is 1/96th second.

The key to reducing the rolling shutter artifact is “asynchronous” CMOS chips that decouple R from T. Ideally, R can then be reduced to a fraction of most T values as is the case with film cameras where the shutter opens and closes very rapidly. Bottom-line, the greater the ratio between a current T value and the chip’s R value, the better.

For example, if the time (R) required to read-out all rows is fixed at 1/120th second (0.00833)—a scan time of 1/60th second—then 24p operation with a shutter-time of 1/48th second (0.020833) will have a higher T/R ratio (2.5 verses 2.0) than would operation where R is 1/96th second (0.01042).

OK -- a ratio of 2.5 isn't that much better than 2.0, but it IS better which supports a claim that EXMOR "can" help reduce rolling shutter.

Note, the EX1 offers Generation 1 EXMOR. Imagine an EXMOR chip that provides four digital output ports just as 3ClearVid now offers four analog ports. Scan time will drop to 1/250th and the ratio will jump to 10.0. Even at 1/60th second we will see a major reduction of rolling shutter.

So rather than see the world as CMOS for consumers and CCD for pros, I think it makes more sense to see the EX1 providing the first iteration of CMOS chips for "pro cameras slightly under $10K." If I'm correct, second or third generation EXMOR chips will offer the benefits of both CCD and CMOS technology and replace CCDs on more expensive pro cameras.

Sony's ability to develop its own imaging chips following a long-range strategy is one of its major capabilities.

Funny how looking backward, helps me to look forward.

Many years back at the CES Show, I remember seeing the first demos of consumer color cameras. At that time, there were two technologies, CCD and MOS.

The sales people showing off the cameras didn't really understand the advantage of solid state image sensors over tubes; lower power, ability to stand greater shock, lighter weight, smaller size, higher reliability, and no high voltage needed.

The only thing that mattered to them was, it didn't do low light as well as tube cameras. A true statement at that time, but we all know that over time, this issue was solved. However, I recall many professional video people preferred tube cameras over solid state, because tube cameras had a "richer image".

Well, CCD was able to reach lower light levels better than MOS, so CCD took over and MOS seemed to come to a dead end. Funny how it came back from the dead as an improved CMOS version.


So now we are at a point where there are trade-offs between the two technologies, but I believe that Steve has hit upon a key point on future improvements. So a faster "shutter" will reduce the impact of the "rolling shutter" and we are VERY likely to see more CMOS improvements in the upcoming years.


This is why I like following technology, it's always getting better and you never know what improvements will come next.


Bob Diaz