How to improve up cam image contrast
Posted: Mon Jul 27, 2015 8:18 am
I had difficulties to get the up cam needle recognition work properly.
My image looked similar to Juhas image in his instructions. http://www.liteplacer.com/setup-uplooki ... rocessing/
The black needle shade was more a medium gray than a dark or black gray. With the result that the surface was not completely filtered out by the threshold.
The problem was that the threshold had to be around 250 to get a almost acceptable result.
I tried reducing the camera brightness with Rezas version. But that also made the needle circle gray.
Analyzing the problem ,I found out that the USB cameras have an automatic exposure. When the overall brightness is low it pulls up the exposure. Just like all digital cameras do. With the result that black becomes gray. Because the down cam is look at the white table surface black is black.
Now the solution:
I covered the up cam hole with a white piece of paper with an approx. 2x2mm hole in the center!
That leads to a lower amplification and to a significantly darker black. The threshold value for the needle recognition could be reduced to 60!!!
BTW: the needle shade is misshaped. It should be a little bit larger to hide the red shrink tubing.
Her you can see the difference:
My image looked similar to Juhas image in his instructions. http://www.liteplacer.com/setup-uplooki ... rocessing/
The black needle shade was more a medium gray than a dark or black gray. With the result that the surface was not completely filtered out by the threshold.
The problem was that the threshold had to be around 250 to get a almost acceptable result.
I tried reducing the camera brightness with Rezas version. But that also made the needle circle gray.
Analyzing the problem ,I found out that the USB cameras have an automatic exposure. When the overall brightness is low it pulls up the exposure. Just like all digital cameras do. With the result that black becomes gray. Because the down cam is look at the white table surface black is black.
Now the solution:
I covered the up cam hole with a white piece of paper with an approx. 2x2mm hole in the center!
That leads to a lower amplification and to a significantly darker black. The threshold value for the needle recognition could be reduced to 60!!!
BTW: the needle shade is misshaped. It should be a little bit larger to hide the red shrink tubing.
Her you can see the difference:
- Before and after applying the white cover
- 2015-07-27 09_08_29-CameraView.png (928.62 KiB) Viewed 3243 times