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CCD Camera Parameters to Consider in Machine Vision
An Overview of Camera Considerations and Imaging Issues
By Miriam van Baalen and Gretchen Alper, Adimec
A dual tap sensor allows for the image to be split in half so that the charge transfer can be completed much more quickly. One of the side effects of using a dual tap camera is a channel mismatch, which is visible as a difference in offset, linearity or sensitivity of the two image halves.
Another effect that can be present with a dual tap sensor is a pixel shift. A pixel shift is a very small apparent spatial shift between the two image halves. Note that this is a very small shift that cannot be seen with the human eye and is much smaller than a pixel.
These side effects of using a multiple tap sensor can influence the accuracy of a measurement. For example, if items that need to be measured lay exactly on the seam of these image halves, both channel mismatch and pixel shift can cause small position and size deviations.
Image Artifacts
Other image artifacts that can affect the quality of the image are smear and blooming. Smear is defined as light leakage into the transfer part of the CCD causing unwanted vertical lines in the image.
Blooming is an overflow of photodiode charge into neighboring pixels. It can occur when trying to image a very bright spot. Instead of an image with circular spot, it is deformed on the bottom.
