Vision – Selection

Selection

Before Selection

Understand the basic theories of imaging and lights.
Determine the geometry, size, color, and mounting height.

Select the right size

The size of the light should be around twice as much as the size of field of view

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Select the right light color

Red, green, and blue are the primary colors of light. They are mutually complement. Objects reflect light of the same color as themselves, but not reflect light of the complementary color at all. Thus, for example, if red light emits on a red object, it will reflect all received red light to be collected by camera. In this way, the object looks white during imaging. If green light is used, however, the red object will reflect all received green light so the object looks black during imaging.

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Appropriate light color can increase or decrease the contrast in gray scale between features and background for better recognition.

To highlight features, light of the complementary color of themselves should be used.
To eliminate unconcerned features, light of the same color as themselves should be used.
Specially, UV light is a good choice in inspection of tiny dust particles, like wafer inspection application.

Example:

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Sample under white lighting

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Under red lighting

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Under blue lighting

Select the right angle

If the light is installed in a wrong angle, imaging would be dark no matter how bright the light is.

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High-angle lighting (burr inspection)

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Low-angle lighting (Pin inspection)

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Low-angle lighting (Pin inspection) Schematic

An ideal image for image processing should have high contrast between features and background. That is to say, in black-and-white imaging, the feature is preferably to be brighter and the background is to be darker. In order to make a feature bright in black-and-white imaging, light reflected by the feature should be collected by camera. Similarly, to make background dark, light reflected by background should avoid being collected by camera.

Select the right height

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Mount higher when using high-angle lights

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Mount lower when using low-angle lights

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