Colour control and filtering
As discussed earlier, colour is often an extremely important consideration. Therefore it is extremely important to select and control the colour of wavelength of an illumination accordingly. If the light source is emitting white light, filters can be used in front of the camera to assure that only wavelengths are allowed to pass through the lens and onto the sensor, that are necessary for the image analysis. One of the most common reasons for filtering is to control ambient light pollution and the suppression of artefacts.
At either ends of the spectrum, filters can be used to block either IR or UV light from interfering with the inspection. Conversely, pass filters can be used to select these wavelengths for specific inspection scenarios.
Specular reflection from flat surfaces is most often polarised parallel to the plane of the reflection. This commonly produces unwanted 'glare' that makes the resulting image more difficult to analyse. Polarisation filters can be used to block these reflections.