The use of colored lighting is of fundamental importance in industrial image processing applications. Different light colors have different effects on colored objects:
If the wavelength of the object approximately matches the light color (e.g. red light color and red object), they cancel each other out, and the object or printing is displayed very bright to white. Conversely, using a complementary color (opposite color), the object can be displayed very dark to black (e.g. blue light color and red object).
Thus, by skillfully matching colored light with the color of the test object, an increase or decrease in contrast can be achieved.
In this task, the tubes of a blood filter are to be checked for blockage. Therefore, it is important to achieve the strongest possible contrast difference between the tubes and the rest of the surface. The best possible contrast difference is achieved with UV light. Due to the short-wave light, the material is reflected or absorbed even at the smallest penetration depth, filtering out the deeper levels and highlighting the surface. Higher wavelengths such as red or infrared are suitable for penetrating deeper into the material and highlighting foreign bodies within the material.
In order to better distinguish scratches on the surface, the printing must be weakened. By using blue light, the printing is highlighted more strongly due to the complementary color red. If, on the other hand, the red printing is illuminated with red light, the printing is weakened. The use of long-wave light (IR) makes it possible to see through colored prints to inspect the underlying surface.
Using blue light on red objects makes the red container and red print appear dark due to the complementary color blue. Thus, only the barcode remains visible. UV light allows the surface of the plastic packaging to be inspected. IR light makes the expiration date print disappear and makes the plastic packaging appear transparent, making the TicTacs more visible.
Different LED colors can highlight or reduce features.