Machine Vision Systems

Illumination Intensity

An important factor for stable image processing is setting the proper illumination intensity. This is determined by the lens aperture, object distance from the light source and camera, shutter speed (line speed), and so on.

Lens Aperture

Aperture allows the brightness of incoming light entering a camera to be varied by adjusting the lens. For example, if the image is dark, a brighter image can be obtained by opening the aperture. However, overdoing this will result in a blurred picture due to general lens properties. Therefore, the wider the aperture is opened, the harder it will be to obtain a sharper image. If the user encounters a dark image, it is equally important to increase the illumination intensity of the light without opening the aperture.

Distance to the Object

Working Distance (WD), the distance between the object and the camera, is essential in order to determine the illumination intensity of the light. As a rule of thumb, as the distance from a light source doubles, the light intensity is reduced by 1/4. Moreover, the larger the light axis, the weaker the illumination intensity of the light illuminating the object surface. If a wide visual field is required and the object is positioned at a long distance, bright or multiple lights should be used.

Shutter Speed

When an object moves rapidly, the shutter speed must be increased to prevent blurred images. However, increased shutter speed also means reduced time for the camera's CCD to acquire an electrical charge. Therefore, if the light is not bright enough, the image will appear dark. When performing a desk test, it is important to check the required illumination intensity by increasing the shutter speed.

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