Browse Prior Art Database

Double Compression

IP.com Disclosure Number: IPCOM000078018D
Original Publication Date: 1972-Oct-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 3 page(s) / 34K

Publishing Venue

IBM

Related People

Grossman, DD: AUTHOR

Abstract

In the known image compression system shown in Fig. 1, there are included an encoder and a decoder, both the encoder and decoder having a memory associated therewith. The memories store information from the most recently displayed frame (or line), and this frame is employed to predict the next frame which is scanned. In this type of system, an error signal is produced which is compressed by a data compression technique. The decoder reexpands the error signal and composes it with the old frame to make a new frame. The new frame is then displayed and stored in Place of the old one. If the input image remains static, the stored frame eventually converges to the exact input image.

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Double Compression

In the known image compression system shown in Fig. 1, there are included an encoder and a decoder, both the encoder and decoder having a memory associated therewith. The memories store information from the most recently displayed frame (or line), and this frame is employed to predict the next frame which is scanned. In this type of system, an error signal is produced which is compressed by a data compression technique. The decoder reexpands the error signal and composes it with the old frame to make a new frame. The new frame is then displayed and stored in Place of the old one. If the input image remains static, the stored frame eventually converges to the exact input image.

In this disclosure, in addition to the use of a data compression technique which is applied to the interframe error signal to thereby minimize transmission costs, a second data compression technique is applied to the frame memory to minimize storage cost. Thus, for example, if a 3-bit differential pulse code modulation is used on the frame memory, the size of this memory can be reduced from 256x256x8 bits to 256x256x3 bits.

It is, of course, to be realized that where differential pulse code modulation is employed, for static input image the contents of the frame memory eventually converge to a very good approximation of the input image, but do not converge to the exact image.

In Fig. 2 there is shown an arrangement for carrying out the storage compression technique. With this technique, approximate A images are compressed into codes C. These codes are then reexpanded as required to produce images B which are approximately the same as A. Thus, images B are approximately-approximately the same as the input image.

The operation of the arrangement is explained below for the case of a static input image.

In the operation of the arrangement, the following events occur in successive time intervals: An error signal E1 is constructed by subtracting the null black image from the new image. The error signal E1 is transmitted and is employed to reconstruct the approximate A1 image, which is displayed as the first approximation to the static input image. The approximate image A1 i...