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ToUcam question

Started by m87, 06/15/2005 02:31AM
Posted 06/15/2005 02:31AM Opening Post
If I look at a single frame from an AVI done with
a ToUcam in 640x480 mode, I see this intermitent pattern
of horizonal stripes. I've seen it from several
ToUcams. The pattern is made of alternate rows
being either high or low, with a peak-to-peak
amplitude of about 10%. The pattern is not stable
at one spot on the detector, but just appears
ramdomly throughout the image.

I'm attaching a blow-up of a small section of a
frame illustrating the pattern. This is from a
flat field. This image has been interpolated 400%
larger just so you can see the pattern, so this looks a
little smoother than the raw original image.

Anyone seen this before or have clues on what causes it?
Or how to get rid of it electronically?

Attached Image:

m87's attachment for post 24968
Posted 06/15/2005 06:35AM #1

I suspect that the power supplied to the camera by the USB port is extremely noisy and creates periodic patterns like you've illustrated. Try reducing the frame rate or using another computer to see if that helps. I reduced the level somewhat on my camera by adding a 0.1 uf bypass capacitor across the USB power pin and ground. In my case, I had a strong "herringbone" pattern at high gain settings and this helped.
Posted 06/15/2005 02:40PM #2
John, I have seen this effect on a different camera - a firewire ccd camera using the same sensor - and was told by the manufacturer that it's caused by the dc reference voltage used in the A to D stage drooping when data is sent over the bus to the host pc.

Most likely it's a power supply problem, as suggested by the other poster.

regards, Anthony