Can anyone explain image sensor throughput? Can you overclock an image sensor?

Hello there. I've found information very lacking on the web that goes into detail about how image throughput of image sensors is derived. My point here is, how much data is streaming from an image sensor? Are video cameras, take the GH2 for instance, do their sensors have the ability to stream higher FPS but are throttled by the ability to write that data to disk?

How much data could come from an image sensor wide open, per second I guess is what I'm trying to figure out.

Cameras like the phantom that record thousands of FPS, are the sensors built differently for the throughput or are they overclocked like a computer cpu?

Anyone lol this is driving me nutts!

There is no clock to overclock.

The limits are the exposure time you have to use to take a shot and the ability of the hardware to read that data from the sensor. There is an internal memory buffer and a processor that reads data, but I would not think of them as a limiting factor. Overclocking the processor that reads data from the sensor would not speed anything up, but it would almost certainly fry the system as none of the circuitry is designed to be overclocked or tolerant of it.

--
StephenG

sjgcit said:

There is no clock to overclock.

The limits are the exposure time you have to use to take a shot and the ability of the hardware to read that data from the sensor. There is an internal memory buffer and a processor that reads data, but I would not think of them as a limiting factor. Overclocking the processor that reads data from the sensor would not speed anything up, but it would almost certainly fry the system as none of the circuitry is designed to be overclocked or tolerant of it.

Click to expand...

Stephen, while a sensor doesn't usually have its own processor to "over-clock" in the usual sense, there is a readout rate associated with it. IIRC, the 10 MP Sony CCD sensors clocked their charge our in two parallel streams at 25 MHz, meaning that 10 MP could be scanned after the exposure was acquired into the charge "buckets" in about two tenths of a second. I don't think that one would want to raise this scan frequency by any significant percentage so as to scan out at say twice the rate as it likely wouldn't work.

CMOS sensors are somewhat different as it isn't the charge that is clocked out but rather an actual analogue voltage which is read, and in fact many of the latest designs have their own per row digital acquisition electronics so that the output external to the sensor is purely digital. Over-clocking would have even more of a meaning for them, especially the latter type, but again I doubt that it would work as the data acquisition is designed to work at a certain rate to a particular accuracy = image quality and this would likely be reduced at a higher rate.

As to special sensors designed for very high frame rates, I suspect that they aren't actually clocked at any higher a rate but are still below 100 MHz in order to keep heat down (especially if they are large sensors) but rather just have more read out streams. Even regular DSLR sensors are being designed with more and more parallel streams with almost all of them having at least two and many of the faster ones to scan having four or even eight streams.

The actual data rate read from the sensor for fully digital output is easy to calculate as in something in the order of a tenth of a second per image times the number of MP times two bytes per photosite (which are likely read out 16 bits or two bytes at a time); the data rate per parallel stream would be this last number divided by the number of streams.

Regards, GordonBGood

The main point I was trying to get to was that a sensor isn't like a CPU that's regulated by a clock speed. Clocks in a CPU are used to regulate operational cycles to maintain synchronisation. Sometimes the hardware can take a higher clock speed than it's rated at and you get more instructions processed per second. There is no related concept in a sensor because the operation it's preforming is quite different - basically one massively parallel measurement followed by by a slow serial data read.

As I type these words I know that Murphy's Law is working hard to provide someone, somewhere who has performed major surgery on a digital camera to prove me wrong. God bless those brave and insane men ( mostly) who have never experienced direct sunlight.

--
StephenG

Thanks for the replies everyone, very helpful. Yeah, as you may have guessed, I'm attempting to figure out how to create a higher FPS camera. I have a general idea of the methods of storing said data (RAM, etc), but I was completely at a loss as to the rate at which frames are coming from the sensor.

It would be pretty cool if it were possible to take a sensor from a 60fps camera and by adding the ability to write 28 gb a second worth of data, suddenly turn it into a 5,000 fps camera ;p

Can't let phantom corner the market forever, now can we?

sjgcit said:

The main point I was trying to get to was that a sensor isn't like a CPU that's regulated by a clock speed. Clocks in a CPU are used to regulate operational cycles to maintain synchronisation. Sometimes the hardware can take a higher clock speed than it's rated at and you get more instructions processed per second. There is no related concept in a sensor because the operation it's preforming is quite different - basically one massively parallel measurement followed by by a slow serial data read.

Click to expand...

Not correct.

Here is an example of a real, live, overclocking by a factor of 2, resulting in roughly twice the FPS:



Sincerely,

Joofa

--
Dj Joofa

Palanza said:

Cameras like the phantom that record thousands of FPS, are the sensors built differently for the throughput or are they overclocked like a computer cpu?

Click to expand...

I think a Phantom sensor is partitioned in multiple areas for separate parallel readouts, sometimes to internal memory to further speed up things, from which it can be later downloaded to a recording medium after acquisition of a shot. A Phantom camera can perhaps have 32-64 such parallel readouts. Lower order readouts such as 2 (dual tap) or 4 (quad tap) are commonly available in many off-the-shelf commercial sensors.

Sincerely,

Joofa

--
Dj Joofa

Posting an image doesn't really tell anyone anything.

Posting a link to an article or some explanation would be better. What hardware was used, for example. How is it different from a digital camera ?

--
StephenG

sjgcit said:

Posting an image doesn't really tell anyone anything.

Posting a link to an article or some explanation would be better. What hardware was used, for example. How is it different from a digital camera ?

Click to expand...

It is from a digital camera! I acquired this image myself.

Sincerely,

Joofa

--
Dj Joofa

Do you think it would be possible to modify an existing sensor in lets say, a panasonic GH2, with a method for writing data faster (say, with RAM), and getting a higher FPS out of it? I want to experiment with higher FPS, and while I feel semi-confident in my understanding of ram and disk write speeds, etc, i think it would be much easier to work off of an already functioning sensor.

Joofa said:

Palanza said:

Cameras like the phantom that record thousands of FPS, are the sensors built differently for the throughput or are they overclocked like a computer cpu?

Click to expand...

I think a Phantom sensor is partitioned in multiple areas for separate parallel readouts, sometimes to internal memory to further speed up things, from which it can be later downloaded to a recording medium after acquisition of a shot. A Phantom camera can perhaps have 32-64 such parallel readouts. Lower order readouts such as 2 (dual tap) or 4 (quad tap) are commonly available in many off-the-shelf commercial sensors.

Sincerely,

Joofa

--
Dj Joofa

Click to expand...

Palanza said:

Do you think it would be possible to modify an existing sensor in lets say, a panasonic GH2, with a method for writing data faster (say, with RAM), and getting a higher FPS out of it? I want to experiment with higher FPS, and while I feel semi-confident in my understanding of ram and disk write speeds, etc, i think it would be much easier to work off of an already functioning sensor.

Click to expand...

I'm not sure if that can be done, at least easily enough. I am also not aware of the sensor in GH2.

Sincerely,

Joofa

--
Dj Joofa

--
StephenG