How do I measure the breadth of a particle?

[Steverino]

IMAQ provides a measurement called Max intercept, which is the "length of the longest segment in the convex hull of a particle (in all possible directions of projection)".

In classical image analysis, Length is defined as the length of a bounding rectangle oriented parallel to the longest axis of the particle. (This appears to be equivalent to the MaxIntercept measurement). Breadth is defined as the width of that rectangle.

Is the breadth measurement as described above available in IMAQ?

Thanks!

[Julie S]

Assuming you have the Vision software, the breadth measurement is available from the bounding rectangle. Use the IMAQ Particle Analysis Report to return the bounding rectangle of the particle, and then pull out the width of the rectangle for the breadth measurement.
Refer to C:\Program Files\National Instruments\LabVIEW\Examples\Vision\2. Functions\Binary Analysis\Particle Analysis Report Example.vi for an example that uses this VI.

Hope this helps -
Julie S
Applications Engineer
National Instruments

[Steverino]

Isn't the bounding rectangle aligned with the horizontal axis? If so, then the width of the rectangle is not an accurate reflection of the breadth.

[Julie S]

For IMAQ Vision, breadth is defined as the distance between the left-most and right-most pixels in a particle, which is equal to the horizontal side of the smallest horizontal rectangle containing the particle.

To get the breadth measurement you refer to, you will have to do some more processing. A possible solution is to get the max intercept edge/angle and then redefine your coordinate space off of it. Then the X and Y axis will be aligned with that edge and you can use the bounding rectangle values as you need them.

-Julie S.

[NoviceS]

Hello
I have a query in this regard. How can we get a realisitc breadth measurement of an object which moves nearer and away from the camera.
Suresh

[David S.]

HI Suresh -

Julie's recommendation to use the Particle Analysis function (in Vision Assistant) is still true.  If you're analyzing a binary particle, there is a measurement available in Vision 7.0+ called Max. Feret Diameter.  This measurement is described as the line segment connecting the two perimeter points that are the furthest apart.  (You can find more information about binary particle measurements in the Vision Concepts Manual.

[NoviceS]

Dear David,
Firgive my ignorance. I have looked into the particle analysis. But my doubt is how can the system get precise measurements when a the object moves to and fro. Do I have to use calibration before the particle analysis ?
Thanks and pls forgive me. I am trying to get some fast solutions and I am left with this forum.
suresh

[David S.]

Hi Suresh -

Particle morphology and analysis are performed on binary particles that result from performing a threshold operation on a grayscale image.  (A compound threshold can be performed on each plane of a color image, too.)  The threshold outputs a binary image, which can be "cleaned up" before analyzing the particles of interest.

One of the conveniences of binary image analysis is that the location of a particle is often irrelevant to whether it appears in the binary image.  That is, if you use the proper thresholding technique, you should be able to pick out the particle you want in any part of the frame.  Then, once you clean up your binary image, you can analyze the position, size, and other characteristics of the particle using the Particle Analysis step.

If you're unfamiliar with using the threshold operation for image analysis, I recommend some reading

Vision Concepts Manual, chp 16
found in C:\Program Files\National Instruments\Vision\Documentation