DSLR Video - how does it work? (techincal)

Started Oct 20, 2009 | Discussions thread
bob elkind Veteran Member • Posts: 5,819
Re: line skipping to due *sensor* analog signal handling speed limits

BJL wrote:

bob elkind wrote:

Why would anyone do line-skipping if what you say is true?

Perhaps because of sensor speed limitations, in particular moving data off the sensor along its edge, where reading all pixels in the 16:9 HD frame would require that analog signals be handled sequentially at rates like 10MP+ times 24 fps+, faster than sensors designed primarily for still images can handle. (Live View can use quick and dirty subsampling in both directions at lower than HD res., with far lower bandwidth needs.)

Your explanation is completely reasonable. Just as reasonable is the explanation that line-skipping poses a much lower image processing power burden than convolution for the purposes of 'down-sampling' or decimation.

Once the image is digitized, video processing speed is easier... partly because a lot of processing can be done in parallel. Look how cheap HD video cameras like Flips can be.

Bingo. You're making the point that comes up in (practically) all the 'video on dSLR' threads: a product designed and optimised for video can 'do video' cheaper and better than a product design with video as an add-on feature. This starts with the sensor and very much includes the 'image processor'.

Yes, digital video processors can be very efficient and inexpensive, if (and a BIG if) the processor is designed (architecturally) for video processing. Optimising an image processing CPU for highest resolution still images is very different than a CPU optimised and designed for video. And yes, the sensor design is different as well.

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Bob Elkind
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