How to achieve greatest contrast in greyscale image - lighting vs exposure?

Question

I'm doing a research project which uses a greyscale machine vision camera (mvBlueFOX) to track the position of various reflective strips which are attached at various sections along the inside of a tubular structure (the picture is worth a thousand words!). The strips are illuminated with a couple of bright LED lights which are mounted coaxially to the camera. On the camera we can manually control aperture (which I have as wide as possible to get all the strips in focus) and in the camera software we can control exposure time and gain (ISO).

After capturing the images we set all pixels below a certain threshold to black to isolate the strips, but this process works best when the image is already as contrasty as possible. Some areas of the tube are more reflective than others (there are brackets and areas of different materials).

My question is, what is the best way to achieve a crisp contrast (as close to black everywhere except strips and white where there are strips) before the processing is applied?

I can control the intensity of the lights (to an extent, there are two lights with two light levels for a total of 3 light intensity levels), exposure time, and gain. I know about the exposure triangle, but is there any benefit to throwing more light at the problem given that the strips don't move fast so a long exposure time is possible?

Any help appreciated!

Answer 1

Yes, you can polarize the light.

Use a polarization filter to maximize the contrast of the light coming into the camera.

You can also polarize the light going out of the illuminator.

By doing this you can limit the light entering the camera to a particular angle which can emphasize or de-emphasize the capture of the reflected light depending on the polarization settings.