除了test文件被我改了外，代码是参考的这个github
原理的话我是从杜克大学网课学的Image and Video Processing: From Mars to Hollywood with a Stop at the Hospital
也可以看这篇博文Jpeg编码完整流程解析
test.cpp
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include "jpeg_encoder.h"
#include <stdlib.h>
//-------------------------------------------------------------------------------
int main()
{
char fname[50]; //用于存放文件名
printf("输入文件名：");
scanf("%s", fname);
JpegEncoder encoder;
//输入的文件必须是24bit的bmp文件，尺寸必须是8的倍数
encoder.readFromBMP(fname);
char foutput[50];//用于存放输出文件名
printf("输出文件名：");
scanf("%s", foutput);
//第二个参数在1~199之间，代表文件压缩程度，数字越大，压缩后的文件体积越小
encoder.encodeToJPG(foutput, 99);
return 0;
}
jpeg_encoder.cpp
#ifdef _MSC_VER
#define _CRT_SECURE_NO_WARNINGS
#endif
#include <stdio.h>
#include <memory.h>
#include <math.h>
#include <iostream>
using namespace std;
#include "jpeg_encoder.h"
namespace {
//-------------------------------------------------------------------------------
const unsigned char Luminance_Quantization_Table[64] =
{
16, 11, 10, 16, 24, 40, 51, 61,
12, 12, 14, 19, 26, 58, 60, 55,
14, 13, 16, 24, 40, 57, 69, 56,
14, 17, 22, 29, 51, 87, 80, 62,
18, 22, 37, 56, 68, 109, 103, 77,
24, 35, 55, 64, 81, 104, 113, 92,
49, 64, 78, 87, 103, 121, 120, 101,
72, 92, 95, 98, 112, 100, 103, 99
};
//-------------------------------------------------------------------------------
const unsigned char Chrominance_Quantization_Table[64] =
{
17, 18, 24, 47, 99, 99, 99, 99,
18, 21, 26, 66, 99, 99, 99, 99,
24, 26, 56, 99, 99, 99, 99, 99,
47, 66, 99, 99, 99, 99, 99, 99,
99, 99, 99, 99, 99, 99, 99, 99,
99, 99, 99, 99, 99, 99, 99, 99,
99, 99, 99, 99, 99, 99, 99, 99,
99, 99, 99, 99, 99, 99, 99, 99
};
//-------------------------------------------------------------------------------
const char ZigZag[64] =
{
0, 1, 5, 6,14,15,27,28,
2, 4, 7,13,16,26,29,42,
3, 8,12,17,25,30,41,43,
9,11,18,24,31,40,44,53,
10,19,23,32,39,45,52,54,
20,22,33,38,46,51,55,60,
21,34,37,47,50,56,59,61,
35,36,48,49,57,58,62,63
};
//-------------------------------------------------------------------------------
const char Standard_DC_Luminance_NRCodes[] = { 0, 0, 7, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0 };
const unsigned char Standard_DC_Luminance_Values[] = { 4, 5, 3, 2, 6, 1, 0, 7, 8, 9, 10, 11 };
//-------------------------------------------------------------------------------
const char Standard_DC_Chrominance_NRCodes[] = { 0, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0 };
const unsigned char Standard_DC_Chrominance_Values[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 };
//-------------------------------------------------------------------------------
const char Standard_AC_Luminance_NRCodes[] = { 0, 2, 1, 3, 3, 2, 4, 3, 5, 5, 4, 4, 0, 0, 1, 0x7d };
const unsigned char Standard_AC_Luminance_Values[] =
{
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
};
//-------------------------------------------------------------------------------
const char Standard_AC_Chrominance_NRCodes[] = { 0, 2, 1, 2, 4, 4, 3, 4, 7, 5, 4, 4, 0, 1, 2, 0x77 };
const unsigned char Standard_AC_Chrominance_Values[] =
{
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
};
}
//-------------------------------------------------------------------------------
JpegEncoder::JpegEncoder()
: m_width(0)
, m_height(0)
, m_rgbBuffer(0)
{
//初始化静态表格
_initHuffmanTables();
}
//-------------------------------------------------------------------------------
JpegEncoder::~JpegEncoder()
{
clean();
}
//-------------------------------------------------------------------------------
void JpegEncoder::clean(void)
{
if(m_rgbBuffer) delete[] m_rgbBuffer;
m_rgbBuffer=0;
m_width=0;
m_height=0;
}
//-------------------------------------------------------------------------------
bool JpegEncoder::readFromBMP(const char* fileName)
{
//清理旧数据
clean();
//BMP 文件格式
#pragma pack(push, 2)
typedef struct {
unsigned short bfType;
unsigned int bfSize;
unsigned short bfReserved1;
unsigned short bfReserved2;
unsigned int bfOffBits;
} BITMAPFILEHEADER;
typedef struct {
unsigned int biSize;
int biWidth;
int biHeight;
unsigned short biPlanes;
unsigned short biBitCount;
unsigned int biCompression;
unsigned int biSizeImage;
int biXPelsPerMeter;
int biYPelsPerMeter;
unsigned int biClrUsed;
unsigned int biClrImportant;
} BITMAPINFOHEADER;
#pragma pack(pop)
//打开文件
FILE* fp = fopen(fileName, "rb");
if (fp == 0) { cout << "false"; return false; }
bool successed=false;
do
{
BITMAPFILEHEADER fileHeader;
BITMAPINFOHEADER infoHeader;
if(1 != fread(&fileHeader, sizeof(fileHeader), 1, fp)) break;
if(fileHeader.bfType!=0x4D42) break;
if(1 != fread(&infoHeader, sizeof(infoHeader), 1, fp)) break;
if(infoHeader.biBitCount!=24 || infoHeader.biCompression!=0) break;
int width = infoHeader.biWidth;
int height = infoHeader.biHeight < 0 ? (-infoHeader.biHeight) : infoHeader.biHeight;
if((width&7)!=0 || (height&7)!=0) break; //必须是8的倍数
int bmpSize = width*height*3;
unsigned char* buffer = new unsigned char[bmpSize];
if(buffer==0) break;
fseek(fp, fileHeader.bfOffBits, SEEK_SET);
if(infoHeader.biHeight>0)
{
for(int i=0; i<height; i++)
{
if(width != fread(buffer+(height-1-i)*width*3, 3, width, fp))
{
delete[] buffer; buffer=0;
break;
}
}
}
else
{
if(width*height != fread(buffer, 3, width*height, fp))
{
delete[] buffer; buffer=0;
break;
}
}
m_rgbBuffer = buffer;
m_width = width;
m_height = height;
successed=true;
}while(false);
fclose(fp);fp=0;
return successed;
}
//-------------------------------------------------------------------------------
bool JpegEncoder::encodeToJPG(const char* fileName, int quality_scale)
{
//尚未读取？
if(m_rgbBuffer==0 || m_width==0 || m_height==0) return false;
//输出文件
FILE* fp = fopen(fileName, "wb");
if(fp==0) return false;
//初始化量化表
_initQualityTables(quality_scale);
//文件头
_write_jpeg_header(fp);
short prev_DC_Y = 0, prev_DC_Cb = 0, prev_DC_Cr = 0;
int newByte=0, newBytePos=7;
for(int yPos=0; yPos<m_height; yPos+=8)
{
for (int xPos=0; xPos<m_width; xPos+=8)
{
char yData[64], cbData[64], crData[64];
short yQuant[64], cbQuant[64], crQuant[64];
//转换颜色空间
_convertColorSpace(xPos, yPos, yData, cbData, crData);
BitString outputBitString[128];
int bitStringCounts;
//Y通道压缩
_foword_FDC(yData, yQuant);
_doHuffmanEncoding(yQuant, prev_DC_Y, m_Y_DC_Huffman_Table, m_Y_AC_Huffman_Table, outputBitString, bitStringCounts);
_write_bitstring_(outputBitString, bitStringCounts, newByte, newBytePos, fp);
//Cb通道压缩
_foword_FDC(cbData, cbQuant);
_doHuffmanEncoding(cbQuant, prev_DC_Cb, m_CbCr_DC_Huffman_Table, m_CbCr_AC_Huffman_Table, outputBitString, bitStringCounts);
_write_bitstring_(outputBitString, bitStringCounts, newByte, newBytePos, fp);
//Cr通道压缩
_foword_FDC(crData, crQuant);
_doHuffmanEncoding(crQuant, prev_DC_Cr, m_CbCr_DC_Huffman_Table, m_CbCr_AC_Huffman_Table, outputBitString, bitStringCounts);
_write_bitstring_(outputBitString, bitStringCounts, newByte, newBytePos, fp);
}
}
_write_word_(0xFFD9, fp); //Write End of Image Marker
fclose(fp);
return true;
}
//-------------------------------------------------------------------------------
void JpegEncoder::_initHuffmanTables(void)
{
memset(&m_Y_DC_Huffman_Table, 0, sizeof(m_Y_DC_Huffman_Table));
_computeHuffmanTable(Standard_DC_Luminance_NRCodes, Standard_DC_Luminance_Values, m_Y_DC_Huffman_Table);
memset(&m_Y_AC_Huffman_Table, 0, sizeof(m_Y_AC_Huffman_Table));
_computeHuffmanTable(Standard_AC_Luminance_NRCodes, Standard_AC_Luminance_Values, m_Y_AC_Huffman_Table);
memset(&m_CbCr_DC_Huffman_Table, 0, sizeof(m_CbCr_DC_Huffman_Table));
_computeHuffmanTable(Standard_DC_Chrominance_NRCodes, Standard_DC_Chrominance_Values, m_CbCr_DC_Huffman_Table);
memset(&m_CbCr_AC_Huffman_Table, 0, sizeof(m_CbCr_AC_Huffman_Table));
_computeHuffmanTable(Standard_AC_Chrominance_NRCodes, Standard_AC_Chrominance_Values, m_CbCr_AC_Huffman_Table);
}
//-------------------------------------------------------------------------------
JpegEncoder::BitString JpegEncoder::_getBitCode(int value)
{
BitString ret;
int v = (value>0) ? value : -value;
//bit 的长度
int length = 0;
for(length=0; v; v>>=1) length++;
ret.value = value>0 ? value : ((1<<length)+value-1);
ret.length = length;
return ret;
};
//-------------------------------------------------------------------------------
void JpegEncoder::_initQualityTables(int quality_scale)
{
if(quality_scale<=0) quality_scale=1;
if(quality_scale>=100) quality_scale=99;
for(int i=0; i<64; i++)
{
int temp = ((int)(Luminance_Quantization_Table[i] * quality_scale + 50) / 100);
if (temp<=0) temp = 1;
if (temp>0xFF) temp = 0xFF;
m_YTable[ZigZag[i]] = (unsigned char)temp;
temp = ((int)(Chrominance_Quantization_Table[i] * quality_scale + 50) / 100);
if (temp<=0) temp = 1;
if (temp>0xFF) temp = 0xFF;
m_CbCrTable[ZigZag[i]] = (unsigned char)temp;
}
}
//-------------------------------------------------------------------------------
void JpegEncoder::_computeHuffmanTable(const char* nr_codes, const unsigned char* std_table, BitString* huffman_table)
{
unsigned char pos_in_table = 0;
unsigned short code_value = 0;
for(int k = 1; k <= 16; k++)
{
for(int j = 1; j <= nr_codes[k-1]; j++)
{
huffman_table[std_table[pos_in_table]].value = code_value;
huffman_table[std_table[pos_in_table]].length = k;
pos_in_table++;
code_value++;
}
code_value <<= 1;
}
}
//-------------------------------------------------------------------------------
void JpegEncoder::_write_byte_(unsigned char value, FILE* fp)
{
_write_(&value, 1, fp);
}
//-------------------------------------------------------------------------------
void JpegEncoder::_write_word_(unsigned short value, FILE* fp)
{
unsigned short _value = ((value>>8)&0xFF) | ((value&0xFF)<<8);
_write_(&_value, 2, fp);
}
//-------------------------------------------------------------------------------
void JpegEncoder::_write_(const void* p, int byteSize, FILE* fp)
{
fwrite(p, 1, byteSize, fp);
}
//-------------------------------------------------------------------------------
void JpegEncoder::_doHuffmanEncoding(const short* DU, short& prevDC, const BitString* HTDC, const BitString* HTAC,
BitString* outputBitString, int& bitStringCounts)
{
BitString EOB = HTAC[0x00];
BitString SIXTEEN_ZEROS = HTAC[0xF0];
int index=0;
// encode DC
int dcDiff = (int)(DU[0] - prevDC);
prevDC = DU[0];
if (dcDiff == 0)
outputBitString[index++] = HTDC[0];
else
{
BitString bs = _getBitCode(dcDiff);
outputBitString[index++] = HTDC[bs.length];
outputBitString[index++] = bs;
}
// encode ACs
int endPos=63; //end0pos = first element in reverse order != 0
while((endPos > 0) && (DU[endPos] == 0)) endPos--;
for(int i=1; i<=endPos; )
{
int startPos = i;
while((DU[i] == 0) && (i <= endPos)) i++;
int zeroCounts = i - startPos;
if (zeroCounts >= 16)
{
for (int j=1; j<=zeroCounts/16; j++)
outputBitString[index++] = SIXTEEN_ZEROS;
zeroCounts = zeroCounts%16;
}
BitString bs = _getBitCode(DU[i]);
outputBitString[index++] = HTAC[(zeroCounts << 4) | bs.length];
outputBitString[index++] = bs;
i++;
}
if (endPos != 63)
outputBitString[index++] = EOB;
bitStringCounts = index;
}
//-------------------------------------------------------------------------------
void JpegEncoder::_write_bitstring_(const BitString* bs, int counts, int& newByte, int& newBytePos, FILE* fp)
{
unsigned short mask[] = {1,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768};
for(int i=0; i<counts; i++)
{
int value = bs[i].value;
int posval = bs[i].length - 1;
while (posval >= 0)
{
if ((value & mask[posval]) != 0)
{
newByte = newByte | mask[newBytePos];
}
posval--;
newBytePos--;
if (newBytePos < 0)
{
// Write to stream
_write_byte_((unsigned char)(newByte), fp);
if (newByte == 0xFF)
{
// Handle special case
_write_byte_((unsigned char)(0x00), fp);
}
// Reinitialize
newBytePos = 7;
newByte = 0;
}
}
}
}
//-------------------------------------------------------------------------------
void JpegEncoder::_convertColorSpace(int xPos, int yPos, char* yData, char* cbData, char* crData)
{
for (int y=0; y<8; y++)
{
unsigned char* p = m_rgbBuffer + (y+yPos)*m_width*3 + xPos*3;
for (int x=0; x<8; x++)
{
unsigned char B = *p++;
unsigned char G = *p++;
unsigned char R = *p++;
yData[y*8+x] = (char)(0.299f * R + 0.587f * G + 0.114f * B - 128);
cbData[y*8+x] = (char)(-0.1687f * R - 0.3313f * G + 0.5f * B );
crData[y*8+x] = (char)(0.5f * R - 0.4187f * G - 0.0813f * B);
}
}
}
//-------------------------------------------------------------------------------
void JpegEncoder::_foword_FDC(const char* channel_data, short* fdc_data)
{
const float PI = 3.1415926f;
for(int v=0; v<8; v++)
{
for(int u=0; u<8; u++)
{
float alpha_u = (u==0) ? 1/sqrt(8.0f) : 0.5f;
float alpha_v = (v==0) ? 1/sqrt(8.0f) : 0.5f;
float temp = 0.f;
for(int x=0; x<8; x++)
{
for(int y=0; y<8; y++)
{
float data = channel_data[y*8+x];
data *= cos((2*x+1)*u*PI/16.0f);
data *= cos((2*y+1)*v*PI/16.0f);
temp += data;
}
}
temp *= alpha_u*alpha_v/m_YTable[ZigZag[v*8+u]];
fdc_data[ZigZag[v*8+u]] = (short) ((short)(temp + 16384.5) - 16384);
}
}
}
//-------------------------------------------------------------------------------
void JpegEncoder::_write_jpeg_header(FILE* fp)
{
//SOI
_write_word_(0xFFD8, fp); // marker = 0xFFD8
//APPO
_write_word_(0xFFE0,fp); // marker = 0xFFE0
_write_word_(16, fp); // length = 16 for usual JPEG, no thumbnail
_write_("JFIF", 5, fp); // 'JFIF\0'
_write_byte_(1, fp); // version_hi
_write_byte_(1, fp); // version_low
_write_byte_(0, fp); // xyunits = 0 no units, normal density
_write_word_(1, fp); // xdensity
_write_word_(1, fp); // ydensity
_write_byte_(0, fp); // thumbWidth
_write_byte_(0, fp); // thumbHeight
//DQT
_write_word_(0xFFDB, fp); //marker = 0xFFDB
_write_word_(132, fp); //size=132
_write_byte_(0, fp); //QTYinfo== 0: bit 0..3: number of QT = 0 (table for Y)
// bit 4..7: precision of QT
// bit 8 : 0
_write_(m_YTable, 64, fp); //YTable
_write_byte_(1, fp); //QTCbinfo = 1 (quantization table for Cb,Cr)
_write_(m_CbCrTable, 64, fp); //CbCrTable
//SOFO
_write_word_(0xFFC0, fp); //marker = 0xFFC0
_write_word_(17, fp); //length = 17 for a truecolor YCbCr JPG
_write_byte_(8, fp); //precision = 8: 8 bits/sample
_write_word_(m_height&0xFFFF, fp); //height
_write_word_(m_width&0xFFFF, fp); //width
_write_byte_(3, fp); //nrofcomponents = 3: We encode a truecolor JPG
_write_byte_(1, fp); //IdY = 1
_write_byte_(0x11, fp); //HVY sampling factors for Y (bit 0-3 vert., 4-7 hor.)(SubSamp 1x1)
_write_byte_(0, fp); //QTY Quantization Table number for Y = 0
_write_byte_(2, fp); //IdCb = 2
_write_byte_(0x11, fp); //HVCb = 0x11(SubSamp 1x1)
_write_byte_(1, fp); //QTCb = 1
_write_byte_(3, fp); //IdCr = 3
_write_byte_(0x11, fp); //HVCr = 0x11 (SubSamp 1x1)
_write_byte_(1, fp); //QTCr Normally equal to QTCb = 1
//DHT
_write_word_(0xFFC4, fp); //marker = 0xFFC4
_write_word_(0x01A2, fp); //length = 0x01A2
_write_byte_(0, fp); //HTYDCinfo bit 0..3 : number of HT (0..3), for Y =0
// bit 4 : type of HT, 0 = DC table,1 = AC table
// bit 5..7 : not used, must be 0
_write_(Standard_DC_Luminance_NRCodes, sizeof(Standard_DC_Luminance_NRCodes), fp); //DC_L_NRC
_write_(Standard_DC_Luminance_Values, sizeof(Standard_DC_Luminance_Values), fp); //DC_L_VALUE
_write_byte_(0x10, fp); //HTYACinfo
_write_(Standard_AC_Luminance_NRCodes, sizeof(Standard_AC_Luminance_NRCodes), fp);
_write_(Standard_AC_Luminance_Values, sizeof(Standard_AC_Luminance_Values), fp); //we'll use the standard Huffman tables
_write_byte_(0x01, fp); //HTCbDCinfo
_write_(Standard_DC_Chrominance_NRCodes, sizeof(Standard_DC_Chrominance_NRCodes), fp);
_write_(Standard_DC_Chrominance_Values, sizeof(Standard_DC_Chrominance_Values), fp);
_write_byte_(0x11, fp); //HTCbACinfo
_write_(Standard_AC_Chrominance_NRCodes, sizeof(Standard_AC_Chrominance_NRCodes), fp);
_write_(Standard_AC_Chrominance_Values, sizeof(Standard_AC_Chrominance_Values), fp);
//SOS
_write_word_(0xFFDA, fp); //marker = 0xFFC4
_write_word_(12, fp); //length = 12
_write_byte_(3, fp); //nrofcomponents, Should be 3: truecolor JPG
_write_byte_(1, fp); //Idy=1
_write_byte_(0, fp); //HTY bits 0..3: AC table (0..3)
// bits 4..7: DC table (0..3)
_write_byte_(2, fp); //IdCb
_write_byte_(0x11, fp); //HTCb
_write_byte_(3, fp); //IdCr
_write_byte_(0x11, fp); //HTCr
_write_byte_(0, fp); //Ss not interesting, they should be 0,63,0
_write_byte_(0x3F, fp); //Se
_write_byte_(0, fp); //Bf
}
jpeg_encoder.h
#ifndef __JPEG_ENCODER_HEADER__
#define __JPEG_ENCODER_HEADER__
class JpegEncoder
{
public:
/** 清理数据 */
void clean(void);
/** 从BMP文件中读取文件，仅支持24bit，长度是8的倍数的文件 */
bool readFromBMP(const char* fileName);
/** 压缩到jpg文件中，quality_scale表示质量，取值范围(0,100), 数字越大压缩比例越高*/
bool encodeToJPG(const char* fileName, int quality_scale);
private:
int m_width;
int m_height;
unsigned char* m_rgbBuffer;
unsigned char m_YTable[64];
unsigned char m_CbCrTable[64];
struct BitString
{
int length;
int value;
};
BitString m_Y_DC_Huffman_Table[12];
BitString m_Y_AC_Huffman_Table[256];
BitString m_CbCr_DC_Huffman_Table[12];
BitString m_CbCr_AC_Huffman_Table[256];
private:
void _initHuffmanTables(void);
void _initCategoryAndBitcode(void);
void _initQualityTables(int quality);
void _computeHuffmanTable(const char* nr_codes, const unsigned char* std_table, BitString* huffman_table);
BitString _getBitCode(int value);
void _convertColorSpace(int xPos, int yPos, char* yData, char* cbData, char* crData);
void _foword_FDC(const char* channel_data, short* fdc_data);
void _doHuffmanEncoding(const short* DU, short& prevDC, const BitString* HTDC, const BitString* HTAC,
BitString* outputBitString, int& bitStringCounts);
private:
void _write_jpeg_header(FILE* fp);
void _write_byte_(unsigned char value, FILE* fp);
void _write_word_(unsigned short value, FILE* fp);
void _write_bitstring_(const BitString* bs, int counts, int& newByte, int& newBytePos, FILE* fp);
void _write_(const void* p, int byteSize, FILE* fp);
public:
JpegEncoder();
~JpegEncoder();
};
#endif