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Selection of machine vision light sources

Some tips for choosing light sources:

Ø If you need greater contrast between the foreground and the background, you can consider using a black and white camera and a color light source.

Ø For ambient light issues, try using a monochromatic light source with a filter.

Ø For shiny surfaces, consider using diffuse dome light

Ø Glitter, flat but rough surface, try with coaxial scattered light

Ø To see the shape of the surface, consider using dark field (low angle)

Ø When testing plastics, try using UV or infrared light

Ø If you need to see features through reflective surfaces, try using a low-angle line light source (dark field).

Ø When a single light source cannot effectively solve the problem, consider using a combined light source.

Choose the angle of the light source:

According to the desired image effect, choose light sources with different incident angles.

High-angle illumination, the overall image is brighter, suitable for objects with non-reflective surfaces;

Low-angle illumination, the image background is black and the features are white, which can highlight the contour of the measured object and the surface concave and convex changes;

Multi-angle illumination, the overall image effect is softer, suitable for curved surface object detection;

Backlight illumination, the image effect is a clear black and white outline of the object being measured, often used for size measurement;

Coaxial light irradiation, the image effect is black features on a bright background, used for detection of highly reflective planar objects;

Select the color of the light source:

Considering the color of the light source and the background color, using light of the same color as the object being measured will make the image brighter (for example: red light makes red objects brighter); using light of the opposite color system to the object being measured will make the image darker (e.g. red light makes blue objects darker).

The longer the wavelength, the stronger the penetrating ability;

The shorter the wavelength, the stronger the diffusion ability;

Infrared has strong penetrating ability and is suitable for detecting objects with poor light transmittance, such as brown oral liquid impurity detection.

UV is sensitive to subtle features on the surface and is suitable for detecting places where the contrast is not obvious enough, such as text detection on edible oil bottles;

Choose the shape and size of your light source:

Mainly divided into round, square and bar shapes;

Normally, a light source with the same shape as the object being measured is selected, and the final light source shape is subject to the test results;

The size of the light source must be selected to ensure uniform light throughout the entire field of view, preferably slightly larger than the field of view.                               

Choose whether to use diffuse light:

If the surface of the object being measured is reflective, it is best to use a diffuse reflection light source.

Multi-angle diffuse illumination makes the overall brightness of the surface of the measured object uniform, the image background is soft, and the detection features are not interfered by the background.