Illumination plays a decisive role in industrial image processing: it determines how well objects are visible, how reliably contrasts are recognized and how accurately the cameras can later perform evaluations. The image quality depends not only on the camera itself, but also to a large extent on how light hits different surfaces and shapes. A basic understanding of these relationships is crucial for efficient and reliable image processing.
The type of surface determines how the light is reflected, scattered or absorbed.
When light hits highly polished surfaces, it is mainly reflected at a uniform angle – just like a mirror. However, even an ideal mirror only reflects around 95% of the light. In image processing, this can lead to bright reflections, overexposure or hotspots, which can affect contrast and cause incorrect evaluations.
Surfaces that are neither highly glossy nor extremely rough scatter the light in many directions, while the majority of photons still follow the reflected angle of incidence. For industrial image processing, this means that illumination must be carefully aligned to avoid shadows or uneven brightness.
Very rough or matt surfaces scatter the light very diffusely. Ideally, the light is distributed evenly in all directions, with the highest intensity occurring perpendicular to the surface. Such surfaces produce a stable and uniform image signal, which facilitates contrast detection.
Not only the material, but also the geometry of the object influences how the camera captures light.
Flat surfaces
Light reflections can be specifically controlled here. If the camera is placed in the reflected angle of incidence of the illumination, most of the light reaches the visual field. Indentations or markings generate a targeted loss of light, which is visible as contrast in the image. This is particularly important when inspecting codes, labels or markings.
Curved or bent surfaces
On curved surfaces, a large proportion of the light photons do not reach the camera. In practice, this means that contrasts are attenuated and evaluation is more difficult. In order to illuminate such surfaces reliably, engineers rely on larger or multidirectional illuminations that illuminate the object evenly from different angles.
Knowledge of light behavior on different surfaces is crucial for many image processing applications:
Image processing thrives on contrasts and contrasts are created by the interplay of light, material and geometry. If you understand how different surfaces reflect and scatter light, you can use illumination in a targeted manner, avoid reflections and improve image quality. In this way, even complex objects can be reliably detected and analyzed, from shiny metal parts to matt plastic surfaces.
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