Variable transfer rate control coding apparatus

Abstract

A variable transfer rate coding apparatus codes moving picture signals of groups of pictures (GOPs). The picture signals are quantized under control of quantization step width and coded. A first code amount per GOP and a second code amount of picture data included GOP are obtained from the coded picture signals. In response to the first code amount, a total code amount of the picture signals of the GOPs are calculated and the total code amount is compared with a reference total code amount, to decide a first target code amount per GOP in order that the total code amount becomes a maximum amount within the reference total code amount. Further, in response to the first target code amount and the second code amount, a second target code amount of the picture data included in each GOP is determined in accordance with the maximum amount. The quantization step width is varied on the basis of the second target code amount.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates to a variable transfer rate control coding apparatus (variable bit coding apparatus) for efficiently coding signals by use of a smaller amount of codes in a digital recording apparatus, and more specifically to a coding apparatus for coding moving picture signals by controlling the transfer rate, that is, the code amount per unit time.2. Description of the Prior ArtIn the high efficiency coding of picture signals, the variable length coding technique is effective and reasonable, because a part of a picture having a small amount of picture data can be coded by use of a smaller amount of codes. In particular, in the case of the interpicture prediction coding in unit of frame or field of moving picture, the amount of codes (often referred to as code amount simply, hereinafter) can be extremely reduced in the motion-less portion of the moving picture. Therefore, it is possible to increase the transmission ...

AI Technical Summary

Benefits of technology

With these problems in mind, therefore, it is the object of the present invention to provide a coding apparatus which can determine an appropriate amount of codes easily so that the picture quality can be improved by uniformalizing the picture quality.

Problems solved by technology

On the other hand, in a block of a small activity, since the pictures change slightly, even a relatively small coding error is easily noticeable.

In the prior art coding apparatus, however, since the quantization step width is determined for each block according to the buffer occupancy, there exists a problem in that the quantization step width changes largely according to the change in the amount of generated codes, with the result that the picture quality is not stable and varies noticeably.

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