Image clipping using Imaq1411 and Pulnix/JAI TM72-EX

[JerryKR]

I am using several Pulnix/JAI TM72-EX cameras with NI Imaq 1411 cards at several test stations, 
and all the stations display the same problem. The resolution of the camera is supposed
to be 768x493 or 758x581, depending upon the mode. I am getting a dead area beyond approximately
640 pixels in the horizontal axis, as shown in the enclosed images. The images were captured from  
custom software, but NI Measurement Explorer shows the same dead area.

We are using the camera in FRM mode, with MGC. Why aren't we
getting the full 758 or 768 pixels?

Thanks, JerryKR

[BruceAmmons · Accepted solution]

Jerry,

This is a problem with analog cameras.  The camera pixel resolution doesn't always correspond to acquired pixel resolution.  The camera may have "skinny" pixels, while the frame grabber reads square pixels.  Your camera is using 758 pixels to generate an analog waveform that is sent to the frame grabber.  The frame grabber digitizes the same waveform into 640 pixels.  If you adjust your pixel clock, you might get some more pixels out of the waveform.

Bruce

[JerryKR]

Your post actually solves two mysteries at the same time.  The stated physical pixel dimensions of the camera are 11.6um horizontal and 13.5um vertical, so we do indeed have 'skinny pixels'.  We noticed that the images were not foreshortened width-wise (circles were still imaged as circles, not ovals).  There must be the pixel rescaling that you mention happening.

Thanks, 

JerryKR

[JerryKR]

Actually, it also raises another question.  Is this a bug in the NI Measurement studio software that it doesn't automatically pick up the re-digitization and scale the image accordingly?

JerryKR

[BruceAmmons]

No bug.  Most signals from cameras like these are 640x480 when they are digitized correctly.  The framegrabber has no idea how many pixels were originally used to create the waveform (and doesn't need to know).  It just knows that if it digitizes at a certain pixel clock frequency, the image will be proportioned correctly.

If you were to discover that your circles were not perfectly round, you could make slight adjustments to the pixel clock to correct it.

The benefit of digital cameras is that there is no re-digitization.  The pixels on the sensor are read and digitized in the camera, then sent back to the PC as digital data.  You don't lose any resolution or detail and get much better quality images for the same size sensor.

Bruce