Patent ID: 6167088
Filing Date: 2000-12-26
Classification: H04N

Abstract:
A method for encoding a sequence of images according to a group of pictures (GOP) information structure to produce a sequence of compressed images, said method comprising the steps of:determining if a frame rate of one or more images of said sequence of images, including said image frame being processed, has been modified according to a 3:2 pull-down process;adapting, in response to said determination, a GOP bit allocation parameter, said bit allocation parameter being indicative of a number of bits remaining in a bit allocation for a current GOP;encoding, using said GOP bit allocation parameter and in accordance with said GOP information structure, said image frames being processed;entering a 24 frames per second (fps) mode of operation by dropping repeated fields from said sequence of images in response to a determination that said sequence of images including said image frames being processed has been subjected to a 3:2 pull-down processing; andentering a 30 frames per second (fps) mode of operation in response to a determination that said sequence of images including said image frame being processed has not been subjected to a 3:2 pull-down processing, wherein:for a first image frame processed after said system exits said 24 fps mode and enters said 30 fps mode, said GOP bit allocation parameter (R) is calculated according to the equation: ##EQU5## where: R.sub.SLACK is a bit utilization overrun or underrun of the previously encoded GOP;""BITRATE"" is the bitrate of a resulting encoded bitstream including said sequence of compressed images;GOP.sub.BITS represents the total number of bits used to encode image frames within the current GOP;n20 is the number of frames within the current GOP that were encoded during said 24 fps mode of operation;n30 is the number of frames within the current GOP that were encoded during said 30 fps mode of operation;nBu is the number of B-frames within the current GOP that remain to be coded in said 30 fps mode;nPu is the number of P-frames that remain to be in said 30 fps mode; andnBo is the number of B-frames that remain to be coded in said 24 fps mode.