Picture decoding method and apparatus

A picture decoding apparatus for decoding moving picture data of a second resolution from compressed picture data of a first resolution lower than the first resolution, obtained on predictive coding by motion prediction in terms of a pre-set pixel block (macro-block) as a unit and on compression coding in terms of a pre-set pixel block (orthogonal transform block) as a unit, comprising:

• first inverse orthogonal transform means for inverse orthogonal transforming an orthogonal transform block of the compressed picture data, orthogonal transformed by an orthogonal transform system (field orthogonal transform mode) associated with the interlaced scanning;
• second inverse orthogonal transform means for inverse orthogonal transforming an orthogonal transform block of said compressed picture data, orthogonal transformed in accordance with an orthogonal transform system (frame orthogonal transform mode) associated with the sequential scanning;
• addition means for summing the compressed picture data, inverse orthogonal transformed by said first inverse orthogonal transform means or said second inverse orthogonal transform means, to motion compensated reference picture data, to output moving picture data of the second resolution;
• storage means for storing moving picture data outputted by said addition means as reference picture data;
• and
• motion compensation means for motion compensating the macro-block of the reference picture data stored in said storage means;
• said first inverse orthogonal transform means inverse orthogonal transforming coefficients of low-frequency components of respective coefficients of said orthogonal transform block;
• said second inverse orthogonal transform means inverse orthogonal transforming coefficients of the totality of frequency components of said orthogonal transform block, separating respective pixels of the inverse orthogonal transformed orthogonal transform block into two pixel blocks associated with interlaced scanning, respectively orthogonal transforming the two separated pixel blocks, inverse orthogonal transforming coefficients of low-frequency components of respective coefficients of the orthogonal transformed two pixel blocks and synthesizing two inverse orthogonal transformed pixel blocks to generate an orthogonal transform block.