In TV images, snow or electronic noise detracts from the picture; in RTR, this random noise can also be present. If the CCD camera is subject to heat, the noise level will rise, detracting from the image. Some CCD cameras are kept at a lower temperature by a special cooling unit. The digital image processor can eliminate electronic noise by a process called frame averaging which is a mathematical process. The image represented by a set of numbers, i.e., is made up of shades of gray, where 0=black and 255=white. Each pixel is, in effect, given a value between zero and 255. True image information stays the same from one frame to the next. If numerical values are averaged from one frame to the next, the bogus value plus the negative effects of random noise are diminished. The data in the tables below illustrate the effect of frame averaging.
Pixel Values of 1st Frame
Pixel Values of 2nd Frame
Pixel Values of Averaged
There are three types of averaging used: integration averaging, averaging, and recursive averaging. Integration averaging requires a still image. Recursive averaging has the advantage that it can be performed on the fly. Number of frames that can be averaged is usually 32 or fewer; with integration and averaging, greater numbers of frames can be dealt with.