1. Field of the Invention
The present invention relates to a video encoding/decoding method and apparatus which encode/decode a fade video and dissolving video, in particular, at high efficiency.
2. Description of the Related Art
Motion compensation predictive inter-frame encoding is used as one of encoding modes in a video encoding standard scheme such as ITU-TH.261, H.263, ISO/IEC MPEG-2, or MPEG-4. As a predictive model in motion compensation predictive inter-frame encoding, a model that exhibits the highest predictive efficiency when no change in brightness occurs in the time direction is used. In the case of a fade video which changes in the brightness of pictures, there is no method known up to now which makes a proper prediction against a change in the brightness of pictures when, for example, a normal picture fades in from a black picture. In order to maintain picture quality in a fade video as well, therefore, a large number of bits are required.
In order to solve this problem, for example, in Japanese Patent No. 3166716, “Fade Countermeasure Video Encoder and Encoding Method”, a fade video part is detected to change the allocation of the number of bits. More specifically, in the case of a fadeout video, a large number of bits are allocated to the start part of fadeout that changes in luminance. In general, the last part of fadeout becomes a monochrome picture, and hence can be easily encoded. For this reason, the number of bits allocated to this part is reduced. This makes it possible to improve the overall picture quality without excessively increasing the total number of bits.
In Japanese Patent No. 2938412, “Video Luminance Change Compensation Method, Video Encoding Apparatus, Video Decoding Apparatus, Recording Medium on Which Video Encoding or Decoding Program Is Recorded, and Recording Medium on Which Encoded Data of Video Is Recorded”, there is proposed an encoding scheme of properly coping with a fade video by compensating for a reference picture in accordance with two parameters, i.e., a luminance change amount and contrast change amount.
In Thomas Wiegand and Berand Girod, “Multi-frame motion-compensated prediction for video transmission”, Kluwer Academic Publishers 2001, an encoding scheme based on a plurality of frame buffers is proposed. In this scheme, an attempt has been made to improve the predictive efficiency by selectively generating a prediction picture from a plurality of reference frames held in the frame buffers.
According to the conventional techniques, in order to encode a fade video or dissolving video while maintaining high picture quality, a large number of bits are required. Therefore, an improvement in encoding efficiency cannot be expected.