Image coding apparatus

摘要

In an image coding apparatus (1), a Hadamard transform unit (11) performs horizontal Hadamard transform on a picture of uncompressed image data (21). The sum total of absolute values of AC component values obtained by the Hadamard transform is calculated as a Hadamard value (23) of the picture. A scene change determination unit (12) determines whether a scene change occurs or not in the picture on the basis of the Hadamard value (23). In a case where a scene change occurs in the picture or where a differential absolute value between the amount of generated codes in a coded GOP and the ideal amount of codes in a GOP is larger than a predetermined reference value, a quantization parameter determination unit (13) determines a quantization parameter (24) of the picture on the basis of the Hadamard value (23) and the target amount of codes of the picture. A coding unit (14) codes the picture by using the determined quantization parameter (24).

主权项

1. An image coding apparatus for coding uncompressed image data on a picture-by-picture basis, comprising:
a Hadamard transform unit configured to calculate a characteristic value of a first picture by performing Hadamard transform on said first picture to generate frequency component data and summing absolute values of AC component values included in said frequency component data; a code amount calculation unit configured to calculate an ideal amount of group codes which is an ideal value of the amount of codes in an image group constituted of a plurality of pictures on the basis of a target bit rate which is set in advance and to calculate a target amount of picture codes which is a target value of the amount of codes to be generated by coding the first picture; a first quantization parameter determination unit configured to determine a quantization parameter to be used for coding of said first picture on the basis of said characteristic value and said target amount of picture codes, a second quantization parameter determination unit configured to determine a quantization parameter of coded leading picture which is positioned at the beginning of an image group and closest to said first picture, to be used as a quantization parameter of said first picture; a determination method selection unit configured to select either one of said first quantization parameter determination unit and said second quantization parameter determination unit on the basis of said ideal amount of group codes and the amount of generated codes in an image group which is coded immediately before an image group including said first picture; and a coding unit configured to code said first picture by using the quantization parameter determined by the quantization parameter determination unit selected by the determination method selection unit.