Apparatus and method for converting signals

Abstract

An image-coding format converting apparatus comprising an EMPEG2 image decoder 30 , a resolution/frame rate converter 31 , a motion vector converter 32 , and an MPEG4 encoder 33 . The EMPEG2 decoder 30 decodes a bit stream of EMPEG2 image codes, generating an image signal. The resolution/frame rate converter 31 converts the image signal. The MPEG4 encoder 33 encodes the output of the resolution/frame rate converter 31 , generating a bit stream of MPEG4 image codes. In the resolution/frame rate converter 31 , pixels are added or extracted in accordance with the start position of a macro block, thus adjusting the input image signal to one than can easily be encoded to MPEG4 image codes. The motion vector converter 32 generates an MPEG4 motion vector from parameters such as an MPEG2 motion vector. The MPEG4 encoder 33 uses the MPEG4 motion vector to encode the output of the resolution/frame rate converter 31.

1 . An apparatus for converting a first encoded image signal to a second encoded image signal, said apparatus comprising: signal-decoding means for decoding the first encoded image signal, thereby outputting an image signal and a first motion vector used in decoding the first encoded image signal; signal-converting means for generating a second image signal from the image signal by resolution converting and frame rate conversion; motion-vector converting means for generating the second motion vector from the second image signal based on the first motion vector; and signal-encoding means for encoding the second image signal into the second encoded image signal, by using the second motion vector. 
     
     
         2 . The apparatus according to  claim 1 , wherein the signal-converting means adds pixels to, or extracts pixels from, the image signal. 
     
     
         3 . A method of converting a first encoded image signal to a second encoded image signal, said method comprising the steps of: decoding the first encoded image signal, thereby outputting an image signal and a first motion vector used in decoding the first encoded image signal; generating a second image signal from the image signal by resolution converting and frame rate conversion; generating the second motion vector from the second image signal based on the first motion vector; and encoding the second image signal into the second encoded image signal, by using the second motion vector. 
     
     
         4 . The method according to  claim 3 , wherein pixels are added to or extracted from the image signal in the step of converting the image signal to a second image signal.