Method of detecting a motion vector in an image coding apparatus

A method of detecting a motion vector, comprising:

• a first step for blocking an input image signal to be coded into a plurality of input blocks each consisting of a plurality of pixels;
• a second step for sub-sampling the input image signal at a predetermined pixel interval, to obtain a sub-sampled image signal;
• a third step for obtaining a sub-sampled input block from the sub-sampled image signal;
• a fourth step for searching in a predetermined range the sub-sampled image signal which has already been subjected to a coding process for a primary block most correlated with the sub-sampled input block, to output a primary motion vector which indicates the primary block most correlated with the sub-sampled input block;
• and
• a fifth step for controlling at least one of a central position of a searching area and a searching pel accuracy in accordance with a type of the primary motion vector, to search for a secondary block most correlated with one of the input blocks, to output a secondary motion vector.