DSLR Video - how does it work? (techincal)

Started Oct 20, 2009 | Discussions thread
OP Ola Forsslund Regular Member • Posts: 451
Read what DSPographer wrote instead

tko wrote:

Let me step in with my guess.

Sure!

First of, 10 FPS is a mirror and bandwidth limitation, not a sensor limitation. I believe the sensors are read out at the full video rate, and don't skip anything.

It is the bandwidth of the sensor that is limited. You can see an example of this by studying the Nikon D3, where the mirror can do 11FPS but only a part of the sensor can be used at that frame rate.

Secondly, no one can do true pixel binning at a video rate right now. They are working on it, and Canon has a short note on it, but it is ready yet. Even for SRAW I don't think they do true binning.

HU? I don't understand what you are talking about. For SRAW, I'd guess that is solely a software thing, no binning.

I believe the video processor simply skips rows and column as required. That would mean for noise purposes you are not dealing with a full size, sensor, the effective sensor size probably isn't that much larger than a true video camera.

Exactly, only it is not the video processor that is throwing out data, that would be truelly crazy since there is nothing to gain by doing so.

Maybe my math is too simple but 1080p is 1080 lines, a 7D does 3456, so only 33% of the sensor is used. That would make a 1" sensor into a 1/3" sensor for noise purposes. A good video recorder can have 3 1/3" RGB sensors so at first glance that video recorder should have better noise characteristics.

Your math and conclusion here is absolutely correct. Only the premises does not match what is happening.

So, it seems to me that all pixels at read, and the video conversion just throws away what it can't use.

How you come to that conclusion from your own reason above is beyond me. But just read what DSPographer wrote in the earlier, he has a very good and detailed theory.

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