Encoder, decoder, encoding method and decoding method for color moving image and method of transferring bitstream of color moving image

A color moving-image decoding apparatus for decoding a color moving-image bitstream having first pictures used as reference pictures and second pictures not used as reference pictures in inter-picture predictive encoding, the apparatus comprising:

• a first decoder to decode a luminance signal of each first picture into a progressive moving-image signal whereas decode color-difference signals of the first picture into first moving-image signals having scanning lines decimated to one-half of scanning lines of the progressive moving-image signal;
• and
• a second encoder to encode a luminance signal and also color-difference signals of the second picture into second moving-image signals having scanning lines decimated to one-half of the scanning lines of the progressive moving-image signal.

A color moving-image encoding method of generating a color moving-image bitstream having first pictures used as reference pictures and second pictures not used as reference pictures in inter-picture predictive encoding, comprising the steps of:

• encoding a luminance signal of each first picture into a progressive moving-image signal whereas encoding color-difference signals of the first picture into first moving-image signals having scanning lines decimated to one-half of scanning lines of the progressive moving-image signal;
• and
• encoding a luminance signal and also color-difference signals of the second picture into second moving-image signals having scanning lines decimated to one-half of the scanning lines of the progressive moving-image signal.

A color moving-image decoding method of decoding a color moving-image bitstream having first pictures used as reference pictures and second pictures not used as reference pictures in inter-picture predictive encoding, comprising the steps of:

• decoding a luminance signal of each first picture into a progressive moving-image signal whereas decoding color-difference signals of the first picture into first moving-image signals having scanning lines decimated to one-half of scanning lines of the progressive moving-image signal;
• and
• encoding a luminance signal and also color-difference signals of the second picture into second moving-image signals having scanning lines decimated to one-half of the scanning lines of the progressive moving-image signal.

A method of transferring a color moving-image bitstream having first pictures used as reference pictures and second pictures not used as reference pictures in inter-picture predictive encoding, comprising the step of transferring the color moving-image bitstream carrying first moving-image signals of a luminance signal of each first picture encoded into a progressive moving image signal and color-difference signals of the first picture encoded into first moving-image signals having scanning lines decimated to one-half of scanning lines of the progressive moving-image signal in a spatially vertical direction and also carrying first moving-image signals of a luminance signal and color-difference signals of the second picture encoded into second moving-image signals having scanning lines decimated to one-half of the scanning lines of the progressive moving image signal.