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Vertical bleeding or smearing from a saturated portion of an image
KB Number: 10317
It is sometimes possible to see a faint bright line that extends from the bottom of the image to the top of the image, passing through a light-saturated spot. This article describes this effect, called smear, and how to avoid it.
In the sample image below, a faint bright line can be seen that extends from the bottom to the top of the image, passing through the light saturated spot.
During image readout, image pixels are shifted vertically downard, row by row, through the vertical transfer cells to the readout register. If there is any leakage of charge into an area of the vertical transfer register, it will be picked up and shifted downward, so that every pixel above and below the area will contain this extra charge. The result is a relatively bright vertical stripe across the entire image.
Effect of Integration Time and Lens Aperture on Smear
Smear is often more noticeable when using very short (microsecond) shutter times. This is because the amount of charge collected in the light-sensitive area of the CCD varies based on exposure time, whereas the amount of
Smear may be addressed