Problem with IMAQ PCI-1411 and Sony XC-73

[Shehrzad]

I am having this rather irritating problem capturing monochrome 8bpp
images off of my XC-73 analog camera. This is very much an
intermittent problem and would appear to be some sort of interlacing
problem. Every once in a while I get this "banding" problem, where
every other scan line appears darker than its neighbor (although it is
not completely black). This behavior is best observed when the image
is contrast stretched. So the pattern will be I'll be able to snap 3
good pictures in a row, and then 1 will be bad, then 2 will be good,
then 2 will be bad, etc..

I observe this problem from both the NI MAX interface as well as when
I write my own code that directly calls the IMAQ driver functions. I
am just "snapping" pictures c
onsecutively, I am not "grabbing" nor
"ring-buffering". I am not using a camera description file (I was
unable to find one for the Sony XC-73 - so I have it configured as a
"Generic RS-170".

I'm thinking that due to the interlacing nature and to the sporadic
frequency of occurrence that perhaps this has something to do with my
lighting. Maybe there is adequate lighting when the odd field is
scanned and no light when the even field is scanned? I know next to
nothing about RS-170, I don't even know if it specifies an interlaced
video format. Any help/pointers would be most appreciated!

Thanks,

Shehrzad

[BruceAmmons]

Shehrzad,

What kind of lighting are you using? I have seen variations like you describe when using fluorescent lighting, and also with incandescent lighting when the frame rate didn't match the power frequency. I suspect you are right about the lighting. I can't think of any other reasons for the problem you described.

Bruce

[Shehrzad]

Bruce,

In fact that was my problem. The XC-73 operates at 30 Hz. My strobe
lighting was not triggered at 30 Hz. Once they matched, the
interlacing problem I described went away.

-Shehrzad

Bruce Ammons wrote in message news:<506500000005000000634D0000-1004225886000@exchange.ni.com>...
> Shehrzad,
>
> What kind of lighting are you using? I have seen variations like you
> describe when using fluorescent lighting, and also with incandescent
> lighting when the frame rate didn't match the power frequency. I
> suspect you are right about the lighting. I can't think of any other
> reasons for the problem you described.
>
> Bruce