Edge detection using IMAQ Find Edge/IMAQ Edge Tool 3

Hi,
I have several images with useless background around a rectangular ROI (coordinates unknown!). So I tried using the two VIs mentioned above in order to detect these edges so that I can remove them. Regretfully, this does not work as planned.
IMAQ Find Edge usually finds an edge, but not where it should be. The edge detection is earlier than I want it to be.
IMAQ Edge Tool 3 sometimes does not find an edge at all, sometimes it finds the edge perfectly. Here I use the 'get best edge' option, which delivers the best results with all the images I tested it with.
All the other options are also not changed while running the VI with the images I have.
Does anyone have intimate knowledge of these VIs' algorithms, how they work, how they can be manipulated, ... ?

Hi,
Can you upload an example image?
That would clarify what you're trying to do?
Most of the time a change of mindset solves the problem.
Kind regards,
- Bjorn -
Have fun using LabVIEW... and if you like my answer, please pay me back in Kudo's
LabVIEW 5.1 - LabVIEW 2012

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Edge Detection using Radon Transformation

Hello
Do anyone have an idea about how to detect the edges in an image by using Radon Transformation
Thanks
Nghtcwrlr
********************Kudos are alwayzz Welcome !! ******************

Hi,
Can you upload an example image?
That would clarify what you're trying to do?
Most of the time a change of mindset solves the problem.
Kind regards,
- Bjorn -
Have fun using LabVIEW... and if you like my answer, please pay me back in Kudo's
LabVIEW 5.1 - LabVIEW 2012

IMAQ Find Edge shows straight edge beyond part

Hello
I am working on finding the sides of my simple part with the IMAQ Find Edge tool. To make it simple, I gave my image an extreme threshold with IMAQ Threshold manually set 0 - 230 so My part basically shows up Black against a white background. I set the ROI of the Part from IMAQ Count Objects 2, expanded that ROI by a couple pixels on each corner of the bounding box and input that into my IMAQ Find Edge tool. I have two IMAQ Find Edges, one looking left to right finding all edges and the other top to bottom finding all edges. It took a while, but I have all Straight edges appearing using the results from Find Edge.
What I don't understand is why these lines are longer than the edges of the part sides? I have attached the image to show what I mean. The edges (yellow) are clearly found on the part, but the resulting lines (red) are beyond these points.
Kelsi
Attachments:
Find edges.png ‏7 KB

Also am I setting up my edge detect functions wrong? I am filtering my image so I only see the object, no shadows. I am thresholding the image to basically outline it. Now I am using the edge detect function to find the edges and it can't seem to find them all. I have an object that I set my ROI about it, and I have the settings for the edge detect on very low to detect basically any edges possible. It still does not consistently see the edges of my object.
Is there a more reliable way to consistently see these edges?
Kelsi
Attachments:
edge detect1.png ‏874 KB
edge detect2.png ‏888 KB
edge detect3.png ‏203 KB

Edge detection or gauging?

Hi,
I am working on measuring difference in diameter of small millimeter thick tubes when they are dry and when they are wet. I wish to use image analysis of labview and use edge detection to measure the change in diameter from the original state to their moist state. Can anyone please help me out by naming useful tools I can use to do this. I know of a tool called gauging but I do not know how it works? I was thinking of using pixels to measure the difference as these tubes are 1-5 mm thick in their dry (original) state and when they are wet their diameter only increase on scale of 10-100 micrometers. I have enough optical resolution in the images but I am lost on how to use labview. Any advice would be greatly appreciated.
Thank You

Hi Ognee,
You could definitely use some functions from the Vision Development Module to find the edges of the tubes, and then use a Caliper function to determine the distance between those edges. I'd recommend taking a look at this tutorial about edge detection using the Vision Development Module. I hope this helps!
David S.

Explanation of Edge Detection of Digital Images

Can anyone suggest the best links for the complete explanation of doing edge detection using java.

http://en.wikipedia.org/wiki/Edge_detection
http://forum.java.sun.com/post!reply.jspa?messageID=4371954
If you have specific questions regarding implementing what you learn we will try to help you with those.
regards

Using IMAQ Find Edge and/or IMAQ Find Straight Edges 3 In order to return tip coordinates of a needle

I know that there are functionalities in the two aforementioned functions that allow for start and end points to be found and output after a straight line is found in an ROI. My problem is that these start and end points are with respect to the ROI, and not the the actual object. What I mean by this is that if I have a needle (whose tip is in the ROI) and try to find the corresponding edge, the edge is easy enough to find. However, the red line that is superimposed on the image, representing the found edge is extended past the tip of the needle, and carried until the boundary of the rectangular ROI I am using. Thus when I return the end point, it gives me the end point along the ROI boundary, not the tip of the needle.
If anyone knows how to obtain the coordinates of the actual needle tip using the edge funtions in the post subject line, that would be very helpful and much appreciated!

If the needle is of the same height you can adjust the ROI accordingly. Also by tip do you mean the tip point?

Can I control rotation on IMAQ find Edge?

Hi all,
Im using the IMAQ tools in LabView including the "IMAQ Find Horizontal
Edge" but sometimes it picks up on erroneous edges especially when I
get more specular back in my image (yeah I could do image processing to
get rid of it but I want to eliminate the possibility of it occuring
regardless). So my question is there any way to control it so
that it will only search for edges that are perfectly horizontal or +/-
a few degrees. I cant seem to find any settings for that.
They have edge strength and contrast and what not but nothing for
rotation. Im sure there has to be a way. Any help would be
really apreciated.
Thanks,
Dave

Hello,
While there is not any way to search for an edge at a particular angle of rotation, there are several settings for the Find Horizontal Edge function that could be used to improve its accuracy. I would suggest starting with modifying the contrast and subsampling ratio settings. The contrast determines what pixel intensity change will constitute an edge (increasing this value will require a greater change in pixel values for an edge to be detected) and the subsampling ratio determines the number of rake lines that will be used to detect the edge.
In addition to those parameters, you can also fine-tune the steepness to help determine the size (in pixels) of the transition area. A steeper angle will require a faster transition from one intensity to another to register as an edge. You can also modify the filter width to specify the number of pixels on either side of the edge that are averaged to determine the contrast of the transition.
Take a look at the IMAQ Vision for LabVIEW VI Reference Help for more information about the different parameters that are available with this function. This help file can be loaded by turning on the Context Help for LabVIEW, hovering over the IMAQ Find Horizontal Edge function, and selecting "Click here for More Help."
Regards,
Scott R.
Applications Engineer
National Instruments

IMAQ find straigth edge

Hello,
I try to mesure an edge using the IMAQ Find Straight Edge VI. As seen on the attached image, some of the the edge was left out by the algorithm.
I tried changing some parameters but without luck. Does someone know what parameter should be changed to get the full edge. The algorithm found the bottom edge perfectly.
For my eyes, the upper edge is pretty straight and sharp so I do not understant why the left part was left...
Thanks for your help!!
Vincent
Attachments:
Find_Straigth_Edge.PNG ‏35 KB

Hello Vincent,
It looks like the edge of you image is fairly blury. Maybe changing the kernel size or gap would help. The easiest thing to do would be to open up vision assistant and play around with your algorithm visually.
Regards,
Ian K.
Applications Engineer
National Instruments

IMAQ find edge.vi - proper setting of options

Trying to use IMAQ find edge.vi I still get a weird error saying something about type conflict with typedef "Edge options.ctl". Please see the attached screenshot.
Is it just Labview bug or did I get anything wrong?
Thank you for your help!
Martin Pekar
Solved!
Go to Solution.
Attachments:
screenshot.JPG ‏147 KB
VI_and_data.zip ‏355 KB

You need to modify the element order in your cluster constant that connects to IMAQ Find Edge. The way you would do this is to right-click on the border of the cluster constant and click 'Reorder Clusters in Control...'. If you want to know what you need to order to, use another IMAQ Find Edge, create a constant for the Options input and repeate the steps that I mentioned to see how the elements in the cluster have been ordered in that constant.
Modifying Cluster Element Order
Adnan Zafar
Certified LabVIEW Architect
Coleman Technologies

I need to manipulate only X values of Edge coordinates (IMAQ Find Vertical Edge VI)

In IMAQ Find Vertical Edge VI Edge Coordinates is an array of clusters, but I need to manipulate only the X values. How can I extrapolate those values to use them after?

Thanks for your answer...I have begin to do it yesterday afternoon, but I don`t finish it yet !!!Isn`t there an other way of doing ? My problem is that I don`t know the exact number of points used by the edge coordinates, and before unbundling the cluster, I have to transform my array of clusters into a cluster, so I have to give it a fixed size...it`s not a difficult work, but quite long...

What exactly is the roundness figure generated by IMAQ Find Circular Edge?

Is it a measure of pixels from the minimum to maximum diameter span of the data points (aka circularity). What numerical figure would a perfect circle return?
~~~~~~~~~~~~~~~~~~~~~~~~~~
"It’s the questions that drive us.”
~~~~~~~~~~~~~~~~~~~~~~~~~~

Hello,
Roundness or residual represents the least square error of the fitted circle to the entire set of points.
The value you would receive if you had a perfect circle would be 0 since there would be no error. You can see the formula for this value if you look at the online help for the IMAQ Fit Cirlce under residual. This is the function that is called by IMAQ Find Circular Edge.
Regards,
Andy Bell
Applications Engineer
National Instruments

IMAQ edge tool 2 "First + last edge" - returns position only of the first edge

I`m using "IMAQ edge tool 2.vi" with Process set to detect "First and last edge. It`s obvious from Edge infromation indicator that it returns only one point coordinates. Where are the coordinates of the last edge detection?
Note: it detects edges along the long green horizontal line, so there are definitevely at least 2 edges.
Thanks for advice.
Martin
Solved!
Go to Solution.
Attachments:
screenshot.JPG ‏42 KB
vi_screenshot.JPG ‏40 KB

Hey Martin,
This may sound silly, but what happens if you scroll to the next entry in your cluster? Right now you are displaying the information for your '0' edge on the front panel. What happens if you index to the '1' edge in your cluster and hence look at the information on the second edge. Is the cluster blank when looking at the 'zero' edge? If it is, perhaps the settings on your find edge step are too strict and the step doesn't pick up on a second edge.
If the problem persists, perhaps posting your sample vi and a sample picture will help clear things up.
Hope this helps!
-Ben
Hope this helps.
-Ben
WaterlooLabs

Use of edge detection in pattern matching algorithm?

Hello all,
I work for a group at Texas A&M University researching two-phase flow in reactors. We have been using IMAQ Vision and had a question regarding the use of edge detection in the pattern matching algorithm. I had seen the webcast entitled “Algorithms that Learn: The Sum and Substance of Pattern Matching and OCR” (http://zone.ni.com/wv/app/doc/p/id/wv-705) and in the webcast it was mentioned that the pattern matching algorithm uses edge detection to, (as best I can tell), reduce the candidate list further and to perform subpixel location calculations. However, I was wondering if this edge detection process is still performed if we do not use the subpixel location calculation (i.e. if we uncheck the “Subpixel Accuracy” check box)? Also, if edge detection is performed in the pattern matching algorithm is it consistent with the method described in Chapter 13 of the Vison Concepts Manual (“Geometric Matching”)? Finally, if edge detection is performed in a manner consistent with Chapter 13 of the manual, how does the geometric matching correlation number affect the correlation calculation that was performed in the previous steps? Are they simply multiplied together?
Many thanks!
-Aaron

Jeff,
We are using Imaq Vision Builder 4, with the included pattern matching that can be accessed via the menus (i.e. we haven't created a custom VI or anything.) We are using the software to locate bubbles during boiling experiments and want a deeper understanding of what is going on "behind the scenes" of the algorithm, as we may have to explain how it works later. We have been able to determine most of what we need from the webcast I had previously mentioned, except for the use of edge detection in the pattern matching algorithm.
At the scales involved in our experiments, subpixel accuracy is really not needed and therefore we do not use it. If edge detection is used in the pattern matching algorithm only to determine location with subpixel accuracy, then we do not really need to know how it works because we do not use that calculation. Inversely, of course, if edge detection is used during pattern matching even without enabling subpixel accuracy, then we would like to have a fairly good understanding of the process.
I've read most of the section on geometric matching in the Vision Concepts Manual and wondered if the process described there for edge detection (or feature matching) was also used in the basic pattern matching algorithm?
To summarize, if edge detection is not used in the basic pattern matching algorithm without subpixel accuracy, then that is all I need to know. If edge detection is used for pattern matching even without using the subpixel accuracy calculation, then we would like to learn more about how exactly it is used in the pattern matching algorithm.
We would really appreciate any help you could give us... we've been digging around on the NI website for a couple of weeks now trying to fit together all the pieces of the pattern matching puzzle.
Many thanks!
Aaron

Automating Edge Detection?

I have a question about the IMAQ edge detection VI. I am designing a VI that will be counting edges in an image many times in succession. My question is that since the area in question will not change as the image changes, is it possible to just measure along the same line every time? Can I select a start and end pixel location for the edge detection? At this point I have to click and drag a line and it is very tedious for the amount of images that will be measured.
Thanks,
Mack

Hi Mack24,
Which tool are you using for edge detection? The shipping example "Edge Detection.vi" allows you to specify a ROI of a line to detect edges against.
The example can be found under Toolkits and Modules->Vision->Caliper->Edge Detection.vi
-N
National Instruments
Applications Engineer

Edge detection on a moving object

Hi
I have a problem on edge detection. I have a pulley of different types.
Pulleys where Dia is same, but height differs. Pulleys of different dia but the number of teeth (ridges) vary.
I need to identify one type of pulley from the other. I am trying to use the following logic:
1. Locate the base of the pulley (which is distinct) using pattern match
2. Define a co ordinate based on this pattern match.
3. Define edge detection tool using the co ordinate (this is where I am running into a wall)
I have used extracts of examples : battery inspection, gage and fuse inspection
I am not able to define the edge tool (Edge detector under vision assistant 7.1)
I am trying to use the co ordinates, since if the pulley moves a bit, then the edge detector appears away (in Vision assistant)
THE CATCH IS:
I have to do this in VB since Machine vision has to be integrated into existing vb application.
NOTE: attached image of pulley
Now can some one help me PLS
Thanks in advance
Suresh
Attachments:
pulley.png ‏13 KB

Hi Suresh -
I took your image and expanded the background region to make three versions with the pulley in different positions. Then I loaded the three images into Vision Assistant and built a script that finds the teeth of the pulley. Although Vision Assistant can't generate coordinate systems, I used edge detection algorithms to define a placeholder where the coordinate system code should be added.
I chose to use a clamp and midpoint instead of the Pattern Matching tool because of the nature of the image. Silhouetted images are difficult to pattern match, and the vertical line symmetry of the pulley makes it even more difficult to find a unique area of the object that can be recognized repeatedly. Instead, I generally find more success using algorithms that are designed around edge detection. I assumed that the "notch" at the bottom of the pulley will always be present in your images, so I performed a Clamp in the Horizontal Min Caliper to find this notch. The midpoint of this clamp section can be used as the origin of a coordinate system around which the following Edge Detection steps are performed. This allows you to find the teeth of the pulley no matter where it is in the image. (Note that the VA script was built using pulley with BG 3.png.)
The Builder File that was generated from the script gives you all the code you need except for the Caliper function and the Coordinate System functions. I added comments to these sections to show what type of code you will have to add there.
It may not be exactly the application you need to perform, but it should give you a solid starting point. I hope it helps.
David Staab, CLA
Staff Systems Engineer
National Instruments
Attachments:
Pulley Teeth.zip ‏18 KB

Edge detection using IMAQ Find Edge/IMAQ Edge Tool 3

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