Machine vision: shadow measurement technique using a LED
Machine vision: shadow measurement technique using a LED
(OP)
Dear all,
I have been working on a small project in machine vision. From a telecentric collimated illumination using a high power LED with a small etendue, a round object to measure covers an amount of this light and is projected on a CCD camera creating a shadow. From the pattern of intensity distribution on the CCD, I should have the dimensions of my object knowing the size of the pixels, and the distance from object to CCD.
The problem is the transition form dark to white on the CCD: in fact, to detect the edges of the piece I want to measure, I should compute a threshold based on Fresnel diffraction. This threshold is really hard to determine since it is based on partially coherent light (LED).
Is there anyone that have been working with this kind of technique? That would be really nice. Well thanks in advance.
I am new in this forum, I will try and have a look around to help as much as I can do.
Best,
I have been working on a small project in machine vision. From a telecentric collimated illumination using a high power LED with a small etendue, a round object to measure covers an amount of this light and is projected on a CCD camera creating a shadow. From the pattern of intensity distribution on the CCD, I should have the dimensions of my object knowing the size of the pixels, and the distance from object to CCD.
The problem is the transition form dark to white on the CCD: in fact, to detect the edges of the piece I want to measure, I should compute a threshold based on Fresnel diffraction. This threshold is really hard to determine since it is based on partially coherent light (LED).
Is there anyone that have been working with this kind of technique? That would be really nice. Well thanks in advance.
I am new in this forum, I will try and have a look around to help as much as I can do.
Best,





RE: Machine vision: shadow measurement technique using a LED
TTFN
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RE: Machine vision: shadow measurement technique using a LED
Normally, with a coherent light, the threshold is always 0,25. With a totally incoherent bulb illumination, I got a value of 0,5.
Now, since that I am using an LED, a partially coherent light source, the threshold value is osciallating between 0.25 and 0.5.. And the hardest part is how to compute it exactly to not have major errors. I understand that a proper processing for edge detection could give some results, but I will need a threshold value anyway.
RE: Machine vision: shadow measurement technique using a LED
http://www.radiantzemax.com/kb-en/Knowledgebase/Pe...
HTH,
Dan
Han primo incensus
RE: Machine vision: shadow measurement technique using a LED
Thank your for this article, it is really good. However, I still have the same problem in getting the exact value of the threshold.
RE: Machine vision: shadow measurement technique using a LED
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Machine vision: shadow measurement technique using a LED
I hope that it is better explained that way. Thank you by the way.