Why does USB Snap.vi return a black image?

[DBerry]

I am using the USB camera drivers/tools to perform a snap acquire with a Logitech Quick Cam Chat.  If I use the Snap.vi example file in LabVIEW 7.1\examples\IMAQ\imaqUSB examples.llb I get a blank (black) image.  But if I add a for loop in the first frame of the sequence around the snap function and do about 5 iterations before outputing the image to a display everything seems fine.  It seems that i need to do at least 4-5 iterations to get a clean image.  I would like to know whay I can't just do a single snap iteration.

Thanks

Dan Berry

Faculty Research Assistant

Oregon State University

[Jack J.]

Hello Dan,

Certain cameras require a couple of images to be acquired before it can start taking proper images. In these cases though, it is typically not a black image but more of a blury, overexposed or underexposed image. Can you try using the example program on another USB cam? Possibly one with a different manufacturer. If you see this on different camera models, it could be something with the driver.

Ultimately, you might end up having to take the incorrect images into consideration when writing your program.

Regards,

Jack J.
Product Support Engineer
National Instruments

[Bar_code]

Hi jack,

    Im also facing the same black image problem while using USB snap. but im using the mightex usb camera. In that case what might be the problem, whether camera driver which is provided by camera manufacturer or NI usb tool kit?

[RGreg]

I ran into two major headaches using a Mightex USB camera a few months ago.  First, the USB for IMAQ drivers are no longer supported, and NI recommends using the IMAQdx driver set (costs ~$400 for just the IMAQdx driver set if you don't already have it).  Second, the DirectShow driver from Mightex wasn't playing well with IMAQdx - it even crashed MAX once.  So I bought a camera from Thorlabs for about $300 that works without a problem.

FYI, you might want to post to the Machine Vision board for questions like this.

[Bar_code]

Thank you very much for your information Greg,

in Imaq dx i could not control the properties of camera.(ex: i need to control the size of the image) it gives the error like camera not supported to change the attributes. Morever i want to use the snap function instead of using Grab to reduce the CPU usage but i didnt get much information about snap in examples. Is there any possibilites to use the Imaq dx snap?

Kalanga

[RGreg]

IMAQdx Snap is included in the Vision Acquisition Software package (the $400 version I mentioned previously).  

There is a very old KB article that references a list of all the VIs in the package.  The better way to find that list is in the help files:

 

If you want to try out the software, you can download it and use it in eval mode for 30 days or so... 

[MoritzW]

Hey RGreg,

We have the same problem and right now we are thinking about buying a different camera. We are also thinking about buying one of Thorlabs cameras. Is your cameras the 

"Compact USB 2.0 CMOS Cameras

on this website: http://www.thorlabs.de/newgrouppage9.cfm?objectgroup_id=4024?

Thank you and kind regards,

Moritz