Marble slab

[desalando]

I am working on a program which aims to find exact marble slab on a running belt conveyor. Then marble slab cropped from the image and stored in a data base for further processing.

I also trying to extract contour of this marble slab.

I have tried some of the relevant methods (edge detection, gray morphology, etc.) in Vision Assistant,but none was satifying. So, anybody can help me? Thank you very much.

[Hatef.fouladi]

check crack detection

[desalando]

Hello Hatef,
Thank you for your answer but i'm not trying to find the cracks on marble slab but marble slab from image. (please see attachement). Unfortunately there is not enough contrast difference between marble slab and conveyor belt.

[MikeeB]

Depending on how thick the slab is, you could use lighting to make your task easier. A couple of fluorescent strip lights either side of the conveyor, quite low down will white out the conveyor and leave you the slab on a mostly white background.

[desalando]

Hello Mike;
Slabs are 2cm and 3cm thick. 
We have a linescanner camera and using LED line lighting.

Problem is that surface of conveyor belt not homogeneous. Some areas are dark some areas bright (marble dust/powder). Even worse, marble tiles are sometime wet. Then they leave a wet mark (dark area) behind them.

in fact, I should have been able to find what I wanted with the existing methods (edge detection, gray morphology, segmentation, etc.), but I think my knowledge and my experience are not enough yet. Would there be any help in reaching the solution?

[desalando]

Hello MikeeB,

with "quite low down " did you mean Dark field illumination?

[BruceAmmons]

I did a project similar to this, but we took a totally different approach.  If you don't need to do vision analysis on the marble slab, and you just want the profile of the slab, you might want to consider a 3D imaging camera.  A few years ago I used a Sick camera, and I know there are other ones out there.  I think I saw one by Acuity at a trade show this week.  They project a laser line onto your conveyor area and measure the height across the line.  The output is just like a line camera, but it is height measurements instead of brightness.  It was easy to combine the lines into a 3D profile of the object.  All you do is keep everything taller than a centimeter.  You could get the exact shape of the marble slab with no problems.

Bruce

[desalando]

Hello Bruce, 

Thank you for your answer. We need picture of (not just 3D profile) that marple slab.  We need vision analysis on the marble slab after, too. I know that SICK laser camera.

As i said before it should be not so diffucult with the existing methods (filtering, edge detection, gray morphology, segmentation, watershed, etc. etc.), but my knowledge and my experience are not enough yet.

[Hatef.fouladi]

sorry for my first misunderstanding 
any way I could suggest 3 method maybe you can create machine vision with combination of them 
1 use line profile laser to find edge in one part of your image and try to corp image in front of that line based on conveyor speed 
like bellow image schematic 

2 in this method we should create small but long lighting device that emit to slab edge and  make edge glowing 
using small led array or line profile array  are recommended
the schematic should be some thing like that  

3 investigate on slab and convener light abrasion and reflation static   and select light with wavelength that are so far a way in amount for these to subject( some time find such wavelength  in light is impassible but some time work well )
4 use 2 camera and imply 3 stereo vision and photogrametry method  to find slab contour and make data to corp 
image 
I hope these data could help you to solve your issue  

[desalando]

Hello Hatef,

I would like to thank you for the detailed explanations and the time you spent. I really appreciate it.

I will give a try to method 2 (Dark field illumination). Other methods that you suggested are for us not possible. We have already our linescan camera and LED line illumination. I don't know if 3D stereo vision for linescan applications (which we must use) possible is?

Something caught my attention. All suggestions so far are about "image acquisition" (lighting, camera, etc). I know that image acquisition is very important and make easy image processing.

What i really need now is that which image processing methods i use and how i process this images.

Any suggestions?