Video Expert

[PFM]

Hello all,

I know the PIC is fast enough for video applications I am not so sure about the Picaxe. I am looking at the ability to check the focus of a video signal, it could also be used as an auto-focus signal. Basically a video focus meter is the idea.

Any thoughts on the Picaxe speed to process the video.

Regards,

PFM

 

[manuka]

PICAXEs work at pretty pedestrian speeds compared with raw PICs, & typically only a few 1000 operations a second are possible. Hence actually processing video is just a dream, although focusing may have some mileage. But why the quest? All but the meanest cameras have long been autofocus! I've visions however of manual focus PC/Web cam-suggest you elaborate.

 

[hippy]

The question has to be how you would be doing such focusing from just the video signal ? I have no idea, but expect it would involve some quite complex processing and high speeds. The PICAXE unfortunately isn't suited to either and I'd expect a PICmicro to be hard pushed to do the job as well.

 

[PFM]

Thanks,

The cameras in question are CCTV cameras with fixed (not auto focus) lenses. There are focus meters out there but cost big money. These meters are monitoring something in the video signal but I am way weak in the video world. It seems the Picaxe is a bit too slow for this app. Thanks Hippy for the input no point spending time on a no win project.

Regards,

PFM

 

[hippy]

It's usually a good rule of thumb that if someone charges $10K for a product then you're not going to get the same witha $2 chip

I did a bit of reading and it seems the trick is measure how sharp edges are. A slightly out of focus image gives a larger slew to transitions on the video signal, in focus is very fast with minimal slew. With a whole line whizzing by in around 60uS I imagine slew rates are quite hard to measure.

One thing I did think is, if you have suitable hardware, it could measure any largeish transition and deliver up a slew rate for that. Simply capture as many of those as possible so not working at real video frame rates and see what the average slew rates are.

A simple but very fast flip-flop which triggers on a transition starting and delivers a pulse while the transition is in progress would integrated give a measure of how out of focus overall, and that would be running at real time rates. So maybe an RC-integrator can do a cheap and chearful solution with a PICAXE. I wouldn't put money on it though.

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