Pattern Noise

CCD cameras operate by amplifying incredibly small signals representing as little as a few electrons. This makes the camera very sensitive to electronic noise. This noise can be created in the camera or enter the camera on the power or data cables.

Many noise sources are periodic in nature, some form of repeating signal. When this noise interferes with camera operation it shows up in the image as some form of pattern across the image, usually called pattern noise.

To see this noise take a bias image and carefully examine it for any sort of pattern. The electronic noise in a bias frame should be very random in nature and have no pattern apparent to the eye.

One of the usual suspects are the switching power supplies used by many cameras. These power supplies are often used to create the many different voltages a CCD camera requires. If not properly designed and filtered the noise from these power supplies show up as a ripple pattern or a 'wood-grain' pattern in the image.

There is little to do if this happens as the camera is not operating properly, it really should be returned to the manufacturer for repair.

If you have to work around this issue there is something to try. If the noise is drifting through the image, different each frame, you can average many separate frames to create a relatively pattern free image. If the pattern is the same each time averaging images will not work.

Severe power supply noise resulting in a pattern across the image
A pattern noise in an Audine camera resulting from inconsistent camera timing, this noise was usually the same each frame and would not average out
The image above shows a fairly typical pattern noise issue from an Audine camera with noise leaking in from a TEC power supply. As shown the noise is often subtle and can only be seen in an image that has been highly stretched. As faint as it is it will still create a problem when trying to tease faint detail out of the image when processing
Pattern noise in a SciMeasure Little Joe CCD47 camera resulting from electrical interference from a nearby motor that is part of the optical assembly, this noise resulted in an image noise roughly double that without the motor operating