Figure 2 Number of bits required for gray scale rendition at various spatial frequencies to keep each gray scale step below the perception threshold. The lower curve is the lowest signal that can be detected by the visual system, limited by the threshold contrast sensitivity function. As in most compression systems the color information is sent at lower resolutions than the luminance information. Because of the octave width of the bands it is very easy to use only the information above perception threshold for color. This is a low-frame rate at the highest spatial frequencies and a high frame rate for the lowest spatial frequencies.
Color is sent at a lower frame rate than luminance.
In the case of program production it is preferable to use a more modest compression ratio rather than reducing the frame rate in any band in order to preserve the temporal integrity of the program material. The system has been modularized to ease the implementation. This provides a two-dimensional low pass filter function in order to generate a lower resolution rendition of the image. The lower resolution image is then decimated to reduce its size to half that of the original in both the horizontal and vertical direction. The filtering process is repeated recursively to generate a total of three images of progressively lower resolution and smaller size.