Why was rolling shutter invented?

I

ironpony

Carbonite Member
I mean a lot of people including me, hate the limitation of rolling shutter, especially when you want to shoot fast action. But why was it invented at all?

I'm guessing it was built cause it's cheaper, but isn't a rolling shutter more complicated? The classic shutter is essentially a door that opens and closes, where as the rolling one is a complex electronic digital device that scans. So isn't it cheaper to build a door, than it is to build a complex scanning electronic device?

The old classic shutter was doing good. If it ain't broke, don't fix it.
 
No - you kind of got it backwards. The rolling shutter is an unwanted part of the capture process - cameras have never really ever had a shutter, in the same way as the optical to chemical process went. The original focal plane shutter has always had it's own set of design limitations - think back to when they became able to take stills at very fast shutter speeds. The first shutter followed by the second produced a scan exposure that did have implications to fast moving items. Other systems used rotary shutters, and had different problems. We've gone to electronic exposure systems with video, altering the time each receptor is active. CCDs had one set of problems, CMOS had others. Each has good and bad features - often one being perceived as a sales marketing benefit, while the less good features being cited as problems. If you need to shoot fast action, then you need to perhaps just look at different sensor systems.

The rolling shutter in a mechanical system is indeed a complex bit of kit, but in electronics it's just a scanning system. Back in tube days, we were interlacing frames, because at that time, we had to, and the available technology had no better way that was practical. Once chip technology allowed state of charge to be 'recorded' the chip could be made active and read in numerous ways. This does of course mean that the chip is normally exposed then read sequentially, and this produces in a CMOS chip the bent images we now blame on the rolling shutter. I suppose the real explanation is that it's actually not a fault at all - the item we see as 'bent' did indeed move it's place in the frame, and at the time and individual pixel was 'opened up' and then read back, the image was accurate. What we want, but don't get with cmos, is for every pixel to be opened and recorded at the same time - the design of the chip can't do that. A classic mechanical shutter has never opened and closed instantly, and has always been imperfect at high speeds. Stills photographers have moaned about it for years.

CCDs managed high speed movement better, but they have different negative features, don't they.
 
I don't know of any digital cameras in modest budgets that have a phisical shutter. Nothing is moving inside a DSLR when you record video, there's no opening and closing window anywhere. What we call "shutter" is just a digital thing that the sensor does, and it can only do it this way. Unless you use a different sensor (a CCD, or a global-shutter CMOS), which will have severe downsides in other areas (noise, color, DR, price). Life is full of trade-offs.
 
ironpony said:
I mean a lot of people including me, hate the limitation of rolling shutter, especially when you want to shoot fast action. But why was it invented at all?
Click to expand...

It wasn't. What was invented, was CMOS imagers. CMOS has a number of advantages over CCD, but it also has some disadvantages. And one of those is that CMOS has to be read a line at a time, thus "rolling shutter".

Want to learn more? Google is your friend.
 
ironpony said:
I mean a lot of people including me, hate the limitation of rolling shutter, especially when you want to shoot fast action. But why was it invented at all?

I'm guessing it was built cause it's cheaper, but isn't a rolling shutter more complicated? The classic shutter is essentially a door that opens and closes, where as the rolling one is a complex electronic digital device that scans. So isn't it cheaper to build a door, than it is to build a complex scanning electronic device?

The old classic shutter was doing good. If it ain't broke, don't fix it.
Click to expand...

For high end cameras, some do have mechanical shutters in combo with the electronic readout of the imaging cells.

Rolling shutter is an artifact with how the sensor data is read, and is a compromise between sufficiently high speed read out, noise, power consumption, and price of the resulting circuit.

To use your 'door' analogy, the circuits have several doors, which open to several rooms, and so in order that everyone flows out of the building in an orderly fashion, only some doors are open at any given time.
 
Bruce Watson said:
It wasn't. What was invented, was CMOS imagers. CMOS has a number of advantages over CCD, but it also has some disadvantages. And one of those is that CMOS has to be read a line at a time, thus "rolling shutter".

Want to learn more? Google is your friend.
Click to expand...

CCD devices also require more power for their lower noise features... but higher power means either bigger 'battery' or directly connected to 'house power', a negative feature for the DSLR shooter...
 
You mean to tell me there's no little shutter that rolls up and down the sensor? I think you all have it wrong. When I remove the lens my camera has wheels on each side of the sensor, I mean really, how else could the shutter roll. Besides I was just recording a tutorial on how to lube the bearings in my rolling shutter. It's smoother than ever, especially when I do whip pans. I just figure out why they decided to add moire to my camera for free. Canon could charge for that feature.
 
There are a lot of false assumptions and general misinformation in this thread. A rolling shutter and a global shutter are entirely independent from whether a sensor is CMOS or CCD. But it so happens that because of other design considerations that the majority of the time CMOS sensors will be designed with rolling shutters. But they don't have to be.

Here's an article I wrote several years ago:
http://blog.abelcine.com/2009/04/15/the-difference-between-a-global-shutter-and-a-rolling-shutter/

In order to have a global shutter (all photosites read at once), there must be a driver circuit at every single photosite (what later becomes a pixel). This circuit takes up room at the base of the photosite well so there is less space for light gathering (think of a photosite as a little "light bucket"). The percentage of area used for collecting light is referred to as Fill Factor. To increase sensitivity and dynamic range, designers prefer higher Fill Factors. By limiting the number of drivers the Fill Factor can be increased.

A Rolling Shutter does not read "line by line," meaning that it does not wait for an entire line to be read before beginning the next one. If it did the screw created in the image would be incredibly bad and would yield an unwatchable image on non-static subjects. A rolling shutter reads a tiny bit into a line before starting the next one, which in turn is read a tiny bit beofe the next is started, and so on. The result is a diagonal cascade effect, the speed of which is entirely a function of the of the number of drivers employed, the resolution of the sensor and the control circuit working the drivers. The more drivers and the more powerful the circuits, the faster the rolling shutter will read off the sensor.

The RED cameras have rolling shutters, as does the ALEXA, the F3, the F5, the C300 and many, many other cameras. CMOS sensor cameras with Global Shutters include the Phantom Flex and the F55. The Fill Factor effect on sensitivity is apparent between the F5 and the F55. The F5 uses a rolling shutter and enjoys a base rating of 2000 ISO. The F55 employs a global shutter and its sensitivity is 1250 ISO.
 
maranfilms said:
... I just figure out why they decided to add moire to my camera for free. Canon could charge for that feature.
Click to expand...

Anyone wearing a houd's tooth coat or black and white zigzag patterned attire is just 'asking to stand out', and the Moire Effect is really a feature enhancement. I do think that most of the DSLR HD camera makers have left money on the table on that one.

But didn't Canon give 'rainbow' edging for free on some of their offerings... so not only did one have that wonky jaggie image, it was multicolored... boy more money left on the table.
 
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