Video capture or image sensor suggestions

It strikes me that NTSC B&W at 30 fps allows about 60 uSec per scanline, which in turn requires a-d conversion in about 200 nSec. If you have settled the resolution required, which I doubt will exceed 8 bits (depends on dynamic range needed) you now have a large choice of methods.

Don't forget delta modulation, which should be fairly useful for video and largely limits slew rate. The end processing may be fairly complex, but I assume the problem is basic data capture.

In case you are not familiar with it, at the extreme each delta modulation bit tells the destination to slew upward or downward at some rate. It has no dc restoration level. Thus the digital path for such a B&W NTSC image could be as slow as 5 Mbits/sec. Horizontal edges would be seriously mushed. At 7.5 fps the same bit rate could slew at 4x the rate, or the bit rate could be cut to

1.25 Mbps. However the NTSC conversion would require local storage, while the 30 fps rate needs none.

Thought: you could use the horizontal sync time to delta modulate from the rh of picture level to the lh of picture level, if you have some other way of providing horizontal sync. Some ingenious coding assignments could pack the sync levels within the delta bit stream. This complicates things by requiring means of synchronizing bit streams, besides the hor and ver, and the delta itself.

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Chuck F (cbfalconer@yahoo.com) (cbfalconer@worldnet.att.net)
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Hi Chuck,

Thanks for the discussion, but it's not really what I'm after... I'm looking for a somewhat turnkey all-digital solution. Messing about with an analog video signal is a research project beyond my time budget and probably beyond my current ability, also.

The simplest thing to do would be to remove the IR filter from the cameras I have, but it's not possible with the particular sensor in these things.

There are lots of video to USB devices about, but I doubt many have Linux support you could try a cheap frame grabber board if you have a spare PCI slot as people like Sensoray make one with Linux drivers

Avoids the USB bottleneck and allows video camera direct to card in PC. ordereable even online for $175 in one offs. Can do composite or monochrome NTSC/PAL upto four inputs.

They also make a PC/104+ format version.

Frame rate depends on when you take the images.

If however this is a single board Linux with USB and no PCI, all bets are off.

Aren't the Comedia serail cameras easily available and low cost, but serial? I have not checked but that might get you the frame rate you require with a RS232/USB converter as well.

The main people I use are (unfortunately) Omnivision and Sony.

They were easily available in the UK when I last looked. If you think Omnivision are difficult try Sony!

However have you looked at

Others like Kodak and Mitsubishi are usually for those with much deeper pockets.

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Paul Carpenter          | paul@pcserviceselectronics.co.uk
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Unfortunately I don't - this is an SBC as you surmised. The V4L pages abounding on the net list several capture devices that are supported, but none of them are findable - I suspect that there are many such devices around with Linux support through a generic chipset driver, but it's impossible to work out which device uses which chip.. :(

I didn't know they had a serial camera. That name kept coming up in my searches as a manufacturer of Omnivision demo boards, however I haven't yet located a US distributor of those products. I can't actually read most of their website but it seems as if they are wholesale only.

I haven't been able to buy Micron's parts. ST's and Kodak's image sensors are available at Digi-Key, so actually my first port of call was to look at all the parts stocked there. Unfortunately they are all color or otherwise not suitable.

I was really hoping to go the consumer peripheral route.

They are usually sold as kits under other people's names looking for "Serial JPEG camera" usually finds them. I know of a source in europe who primarily is into GSM modules (serial) who have versions with ports for these cameras.

Have a look at

Intertec version Omnivision supplier

or even 'IP cameras' such as

Lots of distributors sem to think cell phone quality colour is all that is needed for everything! I hate to think how many jobs and potential jobs have wasted time trying to beyond this logic to what actually is required to do the job they want.

Some machine vision jobs need high res, some need lower, some need high end dsp, others anything all the way down to simple binary slice.

Too many years of video and computing and still I get people wanting

24bit accurate colour from SVHS recorders, recorded from a simple board camera with lousy lens and even worse lighting.

There may be consumer USB devices, but I have not personally seen any with Linux support, because they are consumer devices. They may exist but I have not seen any.

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Paul Carpenter          | paul@pcserviceselectronics.co.uk
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What I did (rather unintentionally) was to buy new optics for my webcams. It turned out that the old optics had the integrated IR cut-off filter, while the new ones had not. And voi-la, I had IR-sensitive webcams. You could do the same thing, I suppose, but I'd rather check the datasheet of the sensor that your cameras is currently using first to make sure that the IR cut-off filter is not integrated into sensor itself.

Now, to buy new optics, try Fry's (if in the US) or

Regards, Andras Tantos

I think I've found a 95% solution to my problem. I took a chance and bought six cameras similar to this

from an eBay vendor ($100 total, shipped cost). VID=0x0AC8, PID=0x301B, supported under Linux by the spca5xx driver at

The LEDs on the unit are actually white, not IR. There is also some intelligence in the device to adjust the LED intensity based on light input. It appears to be a normal color camera with a low-attenuation IR filter.