Is 10pixels/mm enough for checking curve of a 1mm diameter hole?

[yangyang-rexxar]

Hi

I have target objects looks like light spots whose diameter is 1mm, actually they are holes on plastic surface, there is a light source in it.

I would like to check if the hole is regular round (not so exact), Im not so sure if 10 pixel/mm is enough for this?

[BruceAmmons]

It depends how "round" you need to check.

Try creating a circle with a 10 pixel diameter, and you will see how rough the edge looks.  Is this good enough for your application?  If you start with a high resolution image and reduce the resolution, it should give you an idea of what the edge pixels will look like.

Bruce

[yangyang-rexxar]

Hi Bruce

Thanks for your interpretation.

My targe is a 80mm length product what actually is a body of microphone, there are many lighting holes over the surface, the diameter is 1mm, so far Im not so sure the precision how round it should be, this is decided by the feeling by customer in future. I got a 1360X1024 camera for check 2 mics one time, this means I can get a 1024/80 precision,  you can see attached picture what is a 3D drawing picture, I will get the sample later on.

[BruceAmmons]

If you are looking for roughness on the edges of the holes, it won't be nearly enough resolution.  You would need 10x resolution or more to see details along the edges.

If you are just looking for gross errors, such as a partially blocked hole, it will probably be okay.  The difficulty is that unless you are looking at the hole straight on, you won't know how big it should be to start with.  At the sides, perspective makes the holes look like narrow ellipses.  Are you going to rotate it so all the holes are inspected straight on?

Bruce

[yangyang-rexxar]

Hi Bruce

Current solution is to rotate the unit by a step motor for 10 steps(two columns per step), I would like to take 10 photos(totally 20 columns), for one photo two columns of holes are approximately regular round because these two columns reside the center of the body.  Then to look for lighting holes as objects on ROI(two columns). Then caculate the area of every hole to match the limits(If I do not need to check the edge)? According to your suggestion there are more than 10 pixels on the edge? If yes, my 1024X1360 will not be enough for this I think:(