Optimizing Light for Machine Vision

How do we optimize light for Machine Vision?

The main objective is to generate maximum contrast through the following techniques:

  • Feature Separation (Contrast)
  • We can generate Maximum Contrast for Features of Interest
  • We can generate Minimum Contrast of Features of no interest
  • We can create minimum Sensitivity to Feature and Environment Variation

Filament Example

In this application there is a little glass vile, we are looking at the filament in the vile. We may use the optimizing techniques to run a line tool across the filament and count the transitions to see if it is the right filament inside.

A ball bearing can help identify the amount of  the amount of ambient light?

The first thing a ball bearing can do for you is to tell you where the ambient light is coming from. Because is it spherical, you are seeing everything in the environment from the cameras perspective. A ball bearing can also tell you how uniform your light source is.

Ball Bearing Example

A ball bearing does 2 things for you. The first thing it does is show you where your ambient light is coming from. Because it is a spherical mirror, you are seeing everything in your environment from the cameras perspective. If we have a bright light on the other side of the room it will appear in the reflection of the ball bearing showing the total environment.

A ball bearing will also show how uniform your light source is. In this example it will show from left to right some less uniform light sources to more uniform light sources. If we are trying to evenly illuminate very shiny surfaces that have a lot of contour to them, we are going to need a very uniform light source.

How do I create contrast?

  1. Feature Analysis - We need understand how the light is going to behave in that part and look at the characteristics of the part to see what’s involved
  2. Change Polarity - By changing the direction or spectrum of the light we can make features bright on dark or dark on bright
  3. Uniformity of the Image - If we have a non-uniform image with hot spots and lighter and darker edges, the system will no be very repeatable.

With Colored Parts, what color will make them bright or dark?

The same color light will always make things bright, and opposite color lights will make things dark.  The Color wheel helps us create contrast just with color alone.

Color Wheel Chart

Using the Opposite Light Spectrum will make a part feature appear darker.
Using the same light spectrum will make the part appear lighter.


Examples:

  • If the Part feature you want to make darker is red, use green light.
  • If the part you want to make lighter is green use green light.

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