Laser spot processing
Laksmi from India  [4 posts]
14 year

I"m doing a project  on laser based range finding.  I'm stuck with the spot detection problem.  The brightness of the nearby objects such as plastic bag etc. come very close to that of laser spot(red). On what basis can thresholding be done? How intensity is computed for thresholding? In addition should there be saturation/hue thresholding also?

Hope my doubts would be clarified soon

Thanks & Regards,

Baghdad_boy from New Zealand  [11 posts] 14 year
Hey Lakshmi,

I still haven't used lasers with Roborealm but I can imagine your situation. If you can still distinguish the colour of the laser maybe you can apply a Colour_Filter first. Then after that use the Laser_Spot_detection. The problem arises if the objects such as the plastic bags are also red.

There is also the other possiblity of turning down the exposure on the camera. I remember STeven saying that laser spots over expose on the camera much more than normal light(fair enough) so if you turn down the exposure you will still be able to detect the laser dot as the brightest point.

If you are using a webcam this can be done easily through the settings, otherwise you can put a simple filter in front of the camera lens (maybe sunglasses for something temporary).

Let me know if you need more help :)

Laksmi from India  [4 posts] 14 year
Hello Baghdad_boy,

I'm really thrilled to see your prompt response.  Thank you so much. I have a few more doubts.

Yes, I'm using a color filter in front of the webcam. But the problem is with brightness thresholding.

The problem is to distinguish red spot on a white plastic bag. Due to over brightness the red spot is appearing as white spot whose intensity values are comparable to that of some regions on the bag(due to reflections). I did some experimentations by changing the camera parameters such as saturation, gain and brightness. In addition to these three, one more, ie, contrast can also be adjusted. Now what do you mean by turning down the exposure? Is it to reduce the exposure time? By reducing the gain, the same effect can be achieved, am I right? That I already did but the problem persists. I feel that thresholding on more than one properties such as saturation & degree of redness etc. may solve the issue. What do you think?

I'd be grateful to know your valuable suggestions.


Baghdad_boy from New Zealand  [11 posts] 14 year
Hey Lakshmi,

I have an exposure option on my webcam by going into Options -> Video Capture and then choosing the Camera Control tab. As you said this controls the exposure time. Maybe you don't have this on your settings.

Can you please send me a screenshot of the video you are working on with no filters applied so I can have a play around with it and see what works best.


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