image comression using 8*8 block-oriented DCT

Hi, I need to compress image G using 8 × 8 block-oriented DCT. First apply dct2 on each of the contiguous 8 × 8 blocks of G. The top leftmost term of each transformed block is called the DC term. Quantize all the DC terms of all the blocks as one data set, using a uniform 64-level quantizer. Afterwards, quantize the 9 elements in the 2nd, 3rd, and 4th counterdiagonals of each block with a separate 8-level uniform quantizer, while the remaining 54 elements of each block are zeroed out.