JPEG
Huffman coding of the quantized DCT coefficient
There is a difference in the handling of the first data value (the DC coefficient), and the remaining 63 data values.The coding of the first data value is based on DPCM (Difference Pulse Code Modulation). Its value is stored as the difference between itself and the previous pixel blocks first data value.
The "0" numbers remaining within the 63 remaining AC ceofficients are zero-packed (using a run-length transformation), and are coded with other the DCT coefficients.