1. Field of the Invention
This invention relates to a circuit for horizontally and vertically compressing image signals in an image playback system. Specifically, the invention is directed to a circuit which continually compresses image signals in the form of interlaced scans, even though the image signals are input in the form of progressive scans, wherein the circuit has a simple hardware construction.
The present application is based on Korean Patent Application No. 19232/1996 which is incorporated herein by reference for all purposes.
2. Description of the Related Art
Generally, image playback systems having functions such as a double window, picture-in-picture (PIP), and multichannel, include a compression filter which is a compression circuit for compressing the horizontal and vertical lines of image signals.
FIG. 1 is a block diagram of a prior art vertical compression circuit. This vertical compression circuit includes an analog to digital converter (ADC) 2 for converting an analog image signal input into a digital image signal, a full adder 4 for outputting data after full-adding the output of the ADC 2 and other input data, a line memory 6 for storing the output of the full adder 4, and a selector 8 for controlling the output of line memory 6.
The structure of the compression filter of FIG. I can be represented by the expression "d.sub.n-1 .multidot.h.sub.n-1 +d.sub.n .multidot.h.sub.n +d.sub.n+1 .multidot.h.sub.n+1 ". The variable "h" (i.e., h.sub.n-1, h.sub.n, h.sub.n+1) represents the transfer function. Here, the data d.sub.n+1 at line n+1 is stored as d.sub.n+1 .multidot.h.sub.n+1 after being multiplied by h.sub.n+1. The data d.sub.n at line n is added to d.sub.n+1 .multidot.h.sub.n+1 after being multiplied by h.sub.n, and the sum h.sub.n+1 .multidot.d.sub.n+1 +h.sub.n .multidot.d.sub.n is stored in line memory 6. The data d.sub.n-1 is multiplied by h.sub.n-1 and the result is added to the above sum, and the data h.sub.n+1 .multidot.d.sub.n+1 +h.sub.n .multidot.d.sub.n +h.sub.n-1 .multidot.d.sub.n-1 is stored in an external memory (not shown in the drawings) after being stored in line memory 6.
However, the conventional compression circuit described above has only one image data compression mode, namely a "1/3" compression mode, and it is difficult to extend the compression mode to execute various other compression modes. In cases where image data is progressively input, it must be progressively displayed causing picture tremor during playback.