IMAQ Particle Analysis Reports VI

Question

Hello,
I have written a programme that can take an image, resize it, theshold it and generate an array of particle locations using the IMAQ particle analysis VI. The programme works fine but I was wondering if anyone can answer some questions I have regarding some of the details of how this VI works:
How does the IMAQ Particle Analysis Reports VI calculate the centre of mass of the particles? Naively I would assume it would be the same as the IMAQ Centroid VI which uses the formula x=Sum(x*PixelValue)/Sum(PixelValue), y=Sum(y*PixelValue)/Sum(PixelValue), however in this case it finds the centre of mass of the entire image and not of the individual particles. Does it therefore apply these formulas to automated regions of interest to generate the list of centroided coodinates for each particle or does it use an altogether different method?
Is this the fastest and most computationally efficient way to generate these list of centroided coodinates given that it also calculates several other parameters that I do not need?
Thanks so much! Any help would be greatly appreciated!
Justin     

Answer 1

Hi Justin,
I haven't been able to obtain the formula / algorithm that the VI uses but I found that the particle analysis example in CVI offers some insight into what the function is performing. I've copied the C code for your convience but I found it on this white paper http://www.ni.com/example/26517/en/  - 
Particle Analysis Examples. 
int CVICALLBACK ParticleAnalysis (int panel, int control, int event,
void *callbackData, int eventData1, int eventData2)
switch (event)
case EVENT_COMMIT:
/* Make sure the user has thresholded the image */
if(!thresholdFlag) {
MessagePopup ("Image must be thresholded",
"You must threshold an image before performing the particle analysis.");
return 0;
/* This section of our code shows how to run a basic particle analysis.
imaqGetParticleInfo is used with the parameter IMAQ_BASIC_INFO to get
basic information on each particle in the image. It returns a pointer
to a structure array which contains all of the information for each
particle. Passing IMAQ_ALL_INFO instead of IMAQ_BASIC_INFO will run
a more detailed report on the particles, but will take longer to execute.
For more information on the report structure, see vision.h or the function
panel for imaqGetParticleInfo. */
/* Reset the max value for the control to (2^32)-1 so that consecutive runs
are not limited by the number of objects found in previous runs */
SetCtrlAttribute (panelHandle, PANEL_CURRENT_PARTICLE, ATTR_MAX_VALUE,
4294967295);
/* If we have already called imaqGetParticleInfo and thus created a particle report
we should dispose that report before creating a new one. */
if (particleRptExists)
imaqDispose (particleRpt_Ptr);
particleRpt_Ptr = imaqGetParticleInfo (thresholdImage, FALSE, IMAQ_BASIC_INFO, &particleCount);
particleRptExists = TRUE;
/* Simple user interface management - activate the particle report controls */
SetCtrlAttribute (panelHandle, PANEL_PARTICLE_COUNT, ATTR_DIMMED,
FALSE);
SetCtrlAttribute (panelHandle, PANEL_CURRENT_PARTICLE, ATTR_DIMMED,
FALSE);
SetCtrlAttribute (panelHandle, PANEL_AREA, ATTR_DIMMED,
FALSE);
SetCtrlAttribute (panelHandle, PANEL_CAL_AREA, ATTR_DIMMED,
FALSE);
SetCtrlAttribute (panelHandle, PANEL_TOP, ATTR_DIMMED,
FALSE);
SetCtrlAttribute (panelHandle, PANEL_HEIGHT, ATTR_DIMMED,
FALSE);
SetCtrlAttribute (panelHandle, PANEL_LEFT, ATTR_DIMMED,
FALSE);
SetCtrlAttribute (panelHandle, PANEL_WIDTH, ATTR_DIMMED,
FALSE);
SetCtrlVal (panelHandle, PANEL_PARTICLE_COUNT, particleCount);
/* Set the max value on the index control so that the user does
not try to access particle info for particles that do not exist */
SetCtrlAttribute (panelHandle, PANEL_CURRENT_PARTICLE, ATTR_MAX_VALUE,
particleCount - 1);
/* Simulate an event to immediately update report controls and reset the
report index to zero */
ViewReport (panelHandle, 0,EVENT_COMMIT,NULL,0,0);
SetCtrlVal (panelHandle, PANEL_CURRENT_PARTICLE, 0);
break;
return 0;
Kind Regards,
Lucas
Applications Engineer
National Instruments