The Model 449 Dynamic Video Noise Reduction System provides a running quasi-average, or temporal filtering, of the video signal at its input. More precisely, the value for any given pixel in the unit’s output is determined by the equation:

where Pn is the value of the pixel in the current output frame, Pi is the value of the pixel in the current input frame, Pn-1 is the value of the pixel in the previous output frame, and t is a user selected time constant. This equation is solved for each pixel at the normal video frame rate of 30 times per second. As the user selects larger values for t, the exponentially decaying influence of a given pixel's value in a particular input frame will persist over a longer period of time in subsequent output frames. The Model 449 allows values of t to range from zero (binary 0000) to 15 (binary 1111), making possible temporal filtering of from one to 32,768 (in steps of powers of two) frames on a running basis. The Model 449’s 16-bit grayscale resolution provides 65,536 shades of gray for the filtering process.