1. A method of reducing the size of an image, the method comprising the steps of: (a) partitioning an inputted 2N×2N integer DCT coefficient block I 1 into N×N integer DCT coefficient blocks B 0 , B 1 , B 2 , and B 3 , transforming the partitioned N×N integer DCT coefficient blocks into N×N approximation-DCT-coefficient blocks C 0 , C 1 , C 2 and C 3 and approximation-inverse-DCT-transforming the N×N approximation-DCT-coefficient blocks C 0 , C 1 , C 2 and C 3 into image blocks D 0 , D 1 , D 2 , and D 3 of a space domain; (b) creating 2N×2N image blocks P 0 , P 1 , P 2 , and P 3 by inserting the respective approximation-inverse-DCT-transformed N×N image blocks D 0 , D 1 , D 2 , and D 3 to N×N image blocks having elements of all 0's and approximation-DCT-transforming the created 2N×2N image blocks P 0 , P 1 , P 2 , and P 3 into 2N×2N approximation DCT coefficient blocks Q 0 , Q 1 , Q 2 , and Q 3 ; (c) creating a combined approximation coefficient block Y 0 by summing the 2N×2N approximation DCT coefficient blocks Q 0 , Q 1 , Q 2 , and Q 3 and down-sampling an N×N approximation DCT coefficient block Y 1 of a low frequency component from the created combined approximation coefficient block Y 0 ; (d) separating a post scaling factor PF of the down-sampled N×N approximation DCT coefficient block Y 1 from the down-sampled N×N approximation DCT coefficient block Y 1 ; and (e) transforming portions excluding the post scaling factor PF separated from the down-sampled N×N approximation DCT coefficient block Y 1 into an N×N integer DCT coefficient block O 3 .