Understanding Lighting for Machine Vision

We need to understand what happens to light as it hits the part

We must do a good feature analysis of the particular part we are looking at. We must also understand the characteristics of light and how the features and light interact together to affect the results in machine vision.

Light is Energy and travels in Wavelengths

We need to understand how this energy is perceived to our camera, our eyes and film. Light is measured in Nanometers and a Nonometer = 0.000001mm.

Our Human eye sees a peak at 555 Nanometers

We perceive green as being very bright compared to a camera, in which a lot of cameras can get a different spectral response curve.

Always review the spectral response curve of the camera you are using

The spectral response curve shows what the camera can see. The camera efficiency chart will explain how the camera converts light energy into a charge on your CCD.

The Conservation of Energy Principle

Understanding what happens to light as it hits the part. In a lot of cases the energy is going to change in form but the total amount is going to remain constant.

Developing the thought process of how light is interacting with the Part

1. Does the light Reflect? (Change Direction) –  For example: Shiny metal parts

2. Does the Light Have Absorption? (Changes to Heat)- For example: This is where a certain color of light hitting a part is absorbed into the part so it appears dark to our eye. For example: IF we hit red light on a green PC board it is going to appear black to our eye.

3. How does light Transmit through Parts? (Wavelength passes inchanged) - This describes how light bends as it is going through the part and where is it going. For example: Is the light bending back to the camera or away from the camera

4. Does the light Emit? (Wavelength Changes – i.e. Fluorescent) For example: if you put UV light on a certain part, you will see it glow

Illumination - The key to developing good images is learning how to control reflection

Knowing how the reflection occurs and helping understand and control “hot spots”.

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