MediaInfo源代码分析 5：JPEG解析代码分析

来源：互联网发布：阿里云主机绑定域名编辑：程序博客网时间：2024/06/04 19:55

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MediaInfo源代码分析系列文章列表：

MediaInfo源代码分析 1：整体结构
MediaInfo源代码分析 2：API函数
MediaInfo源代码分析 3：Open()函数
MediaInfo源代码分析 4：Inform()函数
MediaInfo源代码分析 5：JPEG解析代码分析

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本文分析MediaInfo中解码JPEG信息的模块。之前写了几篇文章都是关于MediaInfo主程序的，并没有分析其具体是如何解析不同多媒体文件信息的。在这里分析一下解码JPEG文件的代码。其他格式如BMP，GIF等解析的思路基本上是类似的。

File_Jpeg.h的File_Jpeg类的定义如下所示：

//***************************************************************************// Class File_Jpeg//***************************************************************************//继承 File__Analyzeclass File_Jpeg : public File__Analyze{public :    //In    stream_t StreamKind;    bool     Interlaced;    //Constructor/Destructor    File_Jpeg();private :    //Streams management    void Streams_Accept();    //Buffer - File header    bool FileHeader_Begin();    //Buffer - Synchro    bool Synchronize();    bool Synched_Test();    void Synched_Init();    //Buffer - Demux    #if MEDIAINFO_DEMUX    bool Demux_UnpacketizeContainer_Test() {return Demux_UnpacketizeContainer_Test_OneFramePerFile();}    #endif //MEDIAINFO_DEMUX    //Buffer - Global    void Read_Buffer_Unsynched();    #if MEDIAINFO_SEEK    size_t Read_Buffer_Seek (size_t Method, int64u Value, int64u ID) {return Read_Buffer_Seek_OneFramePerFile(Method, Value, ID);}    #endif //MEDIAINFO_SEEK    //Buffer - Per element//解析头    void Header_Parse();    bool Header_Parser_Fill_Size();//解析数据    void Data_Parse();    //Elements//JPEG中的单元//解析相应的单元，并获得信息    void TEM () {};    void SOC () {}    void SIZ ();    void COD ();    void COC () {Skip_XX(Element_Size, "Data");}    void TLM () {Skip_XX(Element_Size, "Data");}    void PLM () {Skip_XX(Element_Size, "Data");}    void PLT () {Skip_XX(Element_Size, "Data");}    void QCD ();    void QCC () {Skip_XX(Element_Size, "Data");}    void RGN () {Skip_XX(Element_Size, "Data");}    void PPM () {Skip_XX(Element_Size, "Data");}    void PPT () {Skip_XX(Element_Size, "Data");}    void CME () {Skip_XX(Element_Size, "Data");}    void SOT () {Skip_XX(Element_Size, "Data");}    void SOP () {Skip_XX(Element_Size, "Data");}    void EPH () {Skip_XX(Element_Size, "Data");}    void SOD ();    void SOF_();    void S0F0() {SOF_();};    void S0F1() {SOF_();};    void S0F2() {SOF_();};    void S0F3() {SOF_();}    void DHT () {Skip_XX(Element_Size, "Data");}    void S0F5() {SOF_();}    void S0F6() {SOF_();}    void S0F7() {SOF_();}    void JPG () {Skip_XX(Element_Size, "Data");}    void S0F9() {SOF_();}    void S0FA() {SOF_();}    void S0FB() {SOF_();}    void DAC () {Skip_XX(Element_Size, "Data");}    void S0FD() {SOF_();}    void S0FE() {SOF_();}    void S0FF() {SOF_();}    void RST0() {};    void RST1() {};    void RST2() {};    void RST3() {};    void RST4() {};    void RST5() {};    void RST6() {};    void RST7() {};    void SOI () {};    void EOI () {};    void SOS ();    void DQT () {Skip_XX(Element_Size, "Data");}    void DNL () {Skip_XX(Element_Size, "Data");}    void DRI () {Skip_XX(Element_Size, "Data");}    void DHP () {Skip_XX(Element_Size, "Data");}    void EXP () {Skip_XX(Element_Size, "Data");}    void APP0();    void APP0_AVI1();    void APP0_JFIF();    void APP0_JFFF();    void APP0_JFFF_JPEG();    void APP0_JFFF_1B();    void APP0_JFFF_3B();    void APP1();    void APP1_EXIF();    void APP2() {Skip_XX(Element_Size, "Data");}    void APP3() {Skip_XX(Element_Size, "Data");}    void APP4() {Skip_XX(Element_Size, "Data");}    void APP5() {Skip_XX(Element_Size, "Data");}    void APP6() {Skip_XX(Element_Size, "Data");}    void APP7() {Skip_XX(Element_Size, "Data");}    void APP8() {Skip_XX(Element_Size, "Data");}    void APP9() {Skip_XX(Element_Size, "Data");}    void APPA() {Skip_XX(Element_Size, "Data");}    void APPB() {Skip_XX(Element_Size, "Data");}    void APPC() {Skip_XX(Element_Size, "Data");}    void APPD() {Skip_XX(Element_Size, "Data");}    void APPE();    void APPE_Adobe0();    void APPF() {Skip_XX(Element_Size, "Data");}    void JPG0() {Skip_XX(Element_Size, "Data");}    void JPG1() {Skip_XX(Element_Size, "Data");}    void JPG2() {Skip_XX(Element_Size, "Data");}    void JPG3() {Skip_XX(Element_Size, "Data");}    void JPG4() {Skip_XX(Element_Size, "Data");}    void JPG5() {Skip_XX(Element_Size, "Data");}    void JPG6() {Skip_XX(Element_Size, "Data");}    void JPG7() {Skip_XX(Element_Size, "Data");}    void JPG8() {Skip_XX(Element_Size, "Data");}    void JPG9() {Skip_XX(Element_Size, "Data");}    void JPGA() {Skip_XX(Element_Size, "Data");}    void JPGB() {Skip_XX(Element_Size, "Data");}    void JPGC() {Skip_XX(Element_Size, "Data");}    void JPGD() {Skip_XX(Element_Size, "Data");}    void COM () {Skip_XX(Element_Size, "Data");}    //Temp    int8u APPE_Adobe0_transform;    bool  APP0_JFIF_Parsed;    bool  SOS_SOD_Parsed;};

上面代码有以下几个特点：

1.继承了File__Analyze类

2.包含了很多JPEG中的数据单元的解析：DHT()，DQT()等等

下面来分别仔细看看源代码：

1.File__Analyze类代码巨多无比，先不分析。他继承了继承了File__Base

2.看一个解码具体单元的代码：SOF_()

注：SOF0（Start of Image，图像开始）。

SOF0，Start of Frame，帧图像开始

标记代码 2字节固定值0xFFC0

包含9个具体字段：
① 数据长度 2字节 ①~⑥六个字段的总长度
即不包括标记代码，但包括本字段
② 精度 1字节每个数据样本的位数
通常是8位，一般软件都不支持 12位和16位
③ 图像高度 2字节图像高度（单位：像素），如果不支持 DNL 就必须 >0
④ 图像宽度 2字节图像宽度（单位：像素），如果不支持 DNL 就必须 >0
⑤ 颜色分量数 1字节只有3个数值可选
1：灰度图；3：YCrCb或YIQ；4：CMYK
而JFIF中使用YCrCb，故这里颜色分量数恒为3
⑥颜色分量信息颜色分量数×3字节（通常为9字节）
a) 颜色分量ID 1字节
b) 水平/垂直采样因子 1字节高4位：水平采样因子
低4位：垂直采样因子
（曾经看到某资料把这两者调转了）
c) 量化表 1字节当前分量使用的量化表的ID

本标记段中，字段⑥应该重复出现，有多少个颜色分量（字段⑤），就出现多少次（一般为3次）。

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void File_Jpeg::SOF_(){    //Parsing    vector<Jpeg_samplingfactor> SamplingFactors;    int16u Height, Width;    int8u  Resolution, Count;    Get_B1 (Resolution,                                         "P - Sample precision");    Get_B2 (Height,                                             "Y - Number of lines");    Get_B2 (Width,                                              "X - Number of samples per line");    Get_B1 (Count,                                              "Nf - Number of image components in frame");    for (int8u Pos=0; Pos<Count; Pos++)    {        Jpeg_samplingfactor SamplingFactor;        Element_Begin1("Component");        Get_B1 (   SamplingFactor.Ci,                           "Ci - Component identifier"); if (SamplingFactor.Ci>Count) Element_Info1(Ztring().append(1, (Char)SamplingFactor.Ci)); else Element_Info1(SamplingFactor.Ci);        BS_Begin();        Get_S1 (4, SamplingFactor.Hi,                           "Hi - Horizontal sampling factor"); Element_Info1(SamplingFactor.Hi);        Get_S1 (4, SamplingFactor.Vi,                           "Vi - Vertical sampling factor"); Element_Info1(SamplingFactor.Vi);        BS_End();        Skip_B1(                                                "Tqi - Quantization table destination selector");        Element_End0();        //Filling list of HiVi        SamplingFactors.push_back(SamplingFactor);    }    FILLING_BEGIN_PRECISE();        if (Frame_Count==0 && Field_Count==0)        {            Accept("JPEG");            Fill("JPEG");            if (Count_Get(StreamKind_Last)==0)                Stream_Prepare(StreamKind_Last);            Fill(StreamKind_Last, 0, Fill_Parameter(StreamKind_Last, Generic_Format), "JPEG");            Fill(StreamKind_Last, 0, Fill_Parameter(StreamKind_Last, Generic_Codec), "JPEG");            if (StreamKind_Last==Stream_Image)                Fill(Stream_Image, 0, Image_Codec_String, "JPEG", Unlimited, true, true); //To Avoid automatic filling            if (StreamKind_Last==Stream_Video)                Fill(Stream_Video, 0, Video_InternetMediaType, "video/JPEG", Unlimited, true, true);            Fill(StreamKind_Last, 0, Fill_Parameter(StreamKind_Last, Generic_BitDepth), Resolution);            Fill(StreamKind_Last, 0, "Height", Height*(Interlaced?2:1));            Fill(StreamKind_Last, 0, "Width", Width);            //ColorSpace from http://docs.oracle.com/javase/1.4.2/docs/api/javax/imageio/metadata/doc-files/jpeg_metadata.html            switch (APPE_Adobe0_transform)            {                case 0x01 :                            if (Count==3)                                Fill(StreamKind_Last, 0, "ColorSpace", "YUV");                case 0x02 :                            if (Count==4)                                Fill(StreamKind_Last, 0, "ColorSpace", "YCCB");                            break;                default   :                            {                            int8u Ci[256];                            memset(Ci, 0, 256);;                            for (int8u Pos=0; Pos<Count; Pos++)                                Ci[SamplingFactors[Pos].Ci]++;                            switch (Count)                            {                                case 1 :    Fill(StreamKind_Last, 0, "ColorSpace", "Y"); break;                                case 2 :    Fill(StreamKind_Last, 0, "ColorSpace", "YA"); break;                                case 3 :                                                 if (!APP0_JFIF_Parsed && Ci['R']==1 && Ci['G']==1 && Ci['B']==1)                                                       //RGB                                                Fill(StreamKind_Last, 0, "ColorSpace", "RGB");                                            else if ((Ci['Y']==1 && ((Ci['C']==1 && Ci['c']==1)                                                                         //YCc                                                                  || Ci['C']==2))                                                                                       //YCC                                                  || APP0_JFIF_Parsed                                                                                                   //APP0 JFIF header present so YCC                                                  || APPE_Adobe0_transform==0                                                                                           //transform set to YCC                                                  || (SamplingFactors[0].Ci==0 && SamplingFactors[1].Ci==1 && SamplingFactors[2].Ci==2)                                 //012                                                  || (SamplingFactors[0].Ci==1 && SamplingFactors[1].Ci==2 && SamplingFactors[2].Ci==3))                                //123                                                Fill(StreamKind_Last, 0, "ColorSpace", "YUV");                                            break;                                case 4 :                                                 if (!APP0_JFIF_Parsed && Ci['R']==1 && Ci['G']==1 && Ci['B']==1 && Ci['A']==1)                                         //RGBA                                                Fill(StreamKind_Last, 0, "ColorSpace", "RGBA");                                            else if ((Ci['Y']==1 && Ci['A']==1 && ((Ci['C']==1 && Ci['c']==1)                                                           //YCcA                                                                                || Ci['C']==2))                                                                         //YCCA                                                  || APP0_JFIF_Parsed                                                                                                   //APP0 JFIF header present so YCCA                                                  || (SamplingFactors[0].Ci==0 && SamplingFactors[1].Ci==1 && SamplingFactors[2].Ci==2 && SamplingFactors[3].Ci==3)     //0123                                                  || (SamplingFactors[0].Ci==1 && SamplingFactors[1].Ci==2 && SamplingFactors[2].Ci==3 && SamplingFactors[3].Ci==4))    //1234                                                Fill(StreamKind_Last, 0, "ColorSpace", "YUVA");                                            else if (APPE_Adobe0_transform==0)                                                                                          //transform set to CMYK                                                Fill(StreamKind_Last, 0, "ColorSpace", "YCCB");                                            break;                                default:    ;                            }                            }            }            //Chroma subsampling            if ((SamplingFactors.size()==3 || SamplingFactors.size()==4) && SamplingFactors[1].Hi==1 && SamplingFactors[2].Hi==1 && SamplingFactors[1].Vi==1 && SamplingFactors[2].Vi==1)            {                string ChromaSubsampling;                switch (SamplingFactors[0].Hi)                {                    case 1 :                            switch (SamplingFactors[0].Vi)                            {                                case 1 : ChromaSubsampling="4:4:4"; break;                                default: ;                            }                            break;                    case 2 :                            switch (SamplingFactors[0].Vi)                            {                                case 1 : ChromaSubsampling="4:2:2"; break;                                case 2 : ChromaSubsampling="4:2:0"; break;                                default: ;                            }                            break;                    case 4 :                            switch (SamplingFactors[0].Vi)                            {                                case 1 : ChromaSubsampling="4:1:1"; break;                                default: ;                            }                            break;                    default: ;                }                if (!ChromaSubsampling.empty())                {                    if (SamplingFactors.size()==4)                    {                        if (ChromaSubsampling=="4:4:4" && SamplingFactors[3].Hi==1 && SamplingFactors[3].Vi==1)                            ChromaSubsampling+=":4";                        else                            ChromaSubsampling+=":?";                    }                    Fill(StreamKind_Last, 0, "ChromaSubsampling", ChromaSubsampling);                }            }        }    FILLING_END();}

从代码的含义可知，提取出了图像的宽，高，采样方式等信息。

详细的代码暂时没有时间研究了，先这样了。