Advanced Imaging

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Advanced Imaging Magazine

Updated: July 8th, 2008 05:26 PM CDT

How To... Choose Correct Illumination

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While struggling with contrast and resolution problems in an imaging system, don't forget proper illumination! Better lighting often improves image quality.

Improper illumination can cause blooming that can hide important image information. Shadowing can do the same, as well as cause false edge calculations. Poor illumination also reduces the signal-to-noise ratio and complicates thresholding.

Got enough light? Every component affects the amount of light that reaches the sensor and, therefore, image quality. For example, as the imaging lens' f/# increases the aperture closes, reducing light to the sensor—so you should increase illumination. Higher-powered lenses image smaller areas, providing less light—add illumination here, as well. The camera's minimum sensitivity determines the minimum amount of light required in the system. In addition, CCD camera settings such as gain and shutter speed also affect the sensor's sensitivity.

There are many different types of illumination, each ideal for different applications. For example, diffuse light from front, axial, or ring lamps provides even illumination of most objects. For shiny objects, diffused or polarizing light can reduce specularity. To highlight topology or defects or texture in flattish objects, structured light works better. Other examples include reducing shadows on bumpy objects, highlighting defects in transparent objects, silhouetting objects, or creating a 3D shape profile.

Correct illumination is critical for imaging systems. Our application engineers can help you further define the illumination requirements of your imaging system.

Kristin Vogt
Applications Engineer
Edmund Optics

www.edmundoptics.com



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