Z型掃描完之後就是huffman熵編碼，實現起來就是查表過程。一共需要建立四張表（AC，DC，luminance，chrominance）。
1、先建立相應size code length統計數組
static BYTE std_dc_luminance_nrcodes[17]={0,0,1,5,1,1,1,1,1,1,0,0,0,0,0,0,0};
static BYTE std_dc_luminance_values[12]={0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11};
static BYTE std_dc_chrominance_nrcodes[17]={0,0,3,1,1,1,1,1,1,1,1,1,0,0,0,0,0};
static BYTE std_dc_chrominance_values[12]={0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11};
static BYTE std_ac_luminance_nrcodes[17]={0,0,2,1,3,3,2,4,3,5,5,4,4,0,0,1,0x7d };
static BYTE std_ac_luminance_values[162]=
{ 0x01, 0x02, 0x03, 0x00, 0x04, 0x11, 0x05, 0x12, 0x21, 0x31, 0x41, 0x06, 0x13, 0x51, 0x61, 0x07, 0x22, 0x71, 0x14, 0x32, 0x81, 0x91, 0xa1, 0x08, 0x23, 0x42, 0xb1, 0xc1, 0x15, 0x52, 0xd1, 0xf0, 0x24, 0x33, 0x62, 0x72, 0x82, 0x09, 0x0a, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2a, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89, 0x8a, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98, 0x99, 0x9a, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7, 0xa8, 0xa9, 0xaa, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7, 0xb8, 0xb9, 0xba, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7, 0xd8, 0xd9, 0xda, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7, 0xe8, 0xe9, 0xea, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9, 0xfa };
static BYTE std_ac_chrominance_nrcodes[17]={0,0,2,1,2,4,4,3,4,7,5,4,4,0,1,2,0x77};
static BYTE std_ac_chrominance_values[162]=
{ 0x00, 0x01, 0x02, 0x03, 0x11, 0x04, 0x05, 0x21, 0x31, 0x06, 0x12, 0x41, 0x51, 0x07, 0x61, 0x71, 0x13, 0x22, 0x32, 0x81, 0x08, 0x14, 0x42, 0x91, 0xa1, 0xb1, 0xc1, 0x09, 0x23, 0x33, 0x52, 0xf0, 0x15, 0x62, 0x72, 0xd1, 0x0a, 0x16, 0x24, 0x34, 0xe1, 0x25, 0xf1, 0x17, 0x18, 0x19, 0x1a, 0x26, 0x27, 0x28, 0x29, 0x2a, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89, 0x8a, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98, 0x99, 0x9a, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7, 0xa8, 0xa9, 0xaa, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7, 0xb8, 0xb9, 0xba, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7, 0xd8, 0xd9, 0xda, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7, 0xe8, 0xe9, 0xea, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9, 0xfa };
2、huffman表建立函數
void compute_Huffman_table(BYTE *nrcodes,BYTE *std_table,bitstring *HT)
{
BYTE k,j;
BYTE pos_in_table;
WORD codevalue;
codevalue=0; pos_in_table=0;
for (k=1;k<=16;k++)
{
for (j=1;j<=nrcodes[k];j++) {HT[std_table[pos_in_table]].value=codevalue;
HT[std_table[pos_in_table]].length=k;
pos_in_table++;
codevalue++;
}
codevalue*=2;//shift
}
}
3、初始化四張表
void init_Huffman_tables()
{
compute_Huffman_table(std_dc_luminance_nrcodes,std_dc_luminance_values,YDC_HT);
compute_Huffman_table(std_dc_chrominance_nrcodes,std_dc_chrominance_values,CbDC_HT);
compute_Huffman_table(std_ac_luminance_nrcodes,std_ac_luminance_values,YAC_HT);
compute_Huffman_table(std_ac_chrominance_nrcodes,std_ac_chrominance_values,CbAC_HT);
}