An image sequence, such as a video image sequence, typically includes a sequence of image frames or pictures. The reproduction of video containing moving objects typically requires a frame speed of thirty image frames per second, with each frame possibly containing in excess of a megabyte of information. Consequently, transmitting or storing such image sequences requires a large amount of either transmission bandwidth or storage capacity. To reduce the necessary transmission bandwidth or storage capacity, the frame sequence is compressed such that redundant information within the sequence is not stored or transmitted. Television, video conferencing and CD-ROM archiving are examples of applications, which can benefit from efficient video sequence encoding.
Additionally, in an image processing environment where processing resources are limited or constrained by the requirements of a particular application, it is necessary to carefully allocate the available coding bits. For example, in real-time application such as videophone, the talking person's face is typically one of the most important part of an image sequence. Additional "important" regions may include edges or boundaries between distinctive objects
For example, the encoding system in a low bit rate application (e.g., real-time application) must efficiently allocate limited bits to address various demands, i.e., allocating bits to code motion information, allocating bits to code texture information, allocating bits to code shape information, allocating bits to code header information and so on. At times, it may be necessary to allocate available bits such that one parameter will benefit at the expense of another parameter, i.e., spending more bits to provide accurate motion information at the expense of spending less bits to provide texture information. Without information as to which regions in a current frame are particularly important, i.e., deserving of more bits from a limited bit pool, the encoder may not allocate the available bits in the most efficient manner.
Therefore, there is a need in the art for an apparatus and a method for classifying regions of an image, based on the relative "importance" of the various areas and to adaptively use the importance information to implement bit allocation in an encoding environment.