提取JPEG图片中的EXIF信息
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//exif.h
/* * File:exif.h * Purpose:cpp EXIF reader * 16/Mar/2003 <ing.davide.pizzolato@libero.it> * based on jhead-1.8 by Matthias Wandel <mwandel(at)rim(dot)net> */#if !defined(__exif_h)#define __exif_h#include <stdlib.h>#include <memory.h>#include <string.h>#include <stdio.h>#include <math.h>#include <malloc.h>#define MAX_COMMENT 1000#define MAX_SECTIONS 20typedef struct tag_ExifInfo { char Version [5]; char CameraMake [32]; char CameraModel [40]; char DateTime [20]; int Height, Width; int Orientation; int IsColor; int Process; int FlashUsed; float FocalLength; float ExposureTime; float ApertureFNumber; float Distance; float CCDWidth; float ExposureBias; int Whitebalance; int MeteringMode; int ExposureProgram; int ISOequivalent; int CompressionLevel; float FocalplaneXRes; float FocalplaneYRes; float FocalplaneUnits; float Xresolution; float Yresolution; float ResolutionUnit; float Brightness; char Comments[MAX_COMMENT]; unsigned char * ThumbnailPointer; /* Pointer at the thumbnail */ unsigned ThumbnailSize; /* Size of thumbnail. */ bool IsExif;} EXIFINFO;//--------------------------------------------------------------------------// JPEG markers consist of one or more 0xFF unsigned chars, followed by a marker// code unsigned char (which is not an FF). Here are the marker codes of interest// in this program. (See jdmarker.c for a more complete list.)//--------------------------------------------------------------------------#define M_SOF0 0xC0 // Start Of Frame N#define M_SOF1 0xC1 // N indicates which compression process#define M_SOF2 0xC2 // Only SOF0-SOF2 are now in common use#define M_SOF3 0xC3#define M_SOF5 0xC5 // NB: codes C4 and CC are NOT SOF markers#define M_SOF6 0xC6#define M_SOF7 0xC7#define M_SOF9 0xC9#define M_SOF10 0xCA#define M_SOF11 0xCB#define M_SOF13 0xCD#define M_SOF14 0xCE#define M_SOF15 0xCF#define M_SOI 0xD8 // Start Of Image (beginning of datastream)#define M_EOI 0xD9 // End Of Image (end of datastream)#define M_SOS 0xDA // Start Of Scan (begins compressed data)#define M_JFIF 0xE0 // Jfif marker#define M_EXIF 0xE1 // Exif marker#define M_COM 0xFE // COMment typedef struct tag_Section_t { unsigned char* Data; int Type; unsigned Size;} Section_t;class Cexif{public: Cexif(EXIFINFO* info = NULL); ~Cexif();public: bool DecodeExif(FILE* hFile); EXIFINFO* m_exifinfo; char m_szLastError[256];protected: bool process_EXIF(unsigned char * CharBuf, unsigned int length); void process_COM(const unsigned char * Data, int length); void process_SOFn(const unsigned char * Data, int marker); int Get16u(void * Short); int Get16m(void * Short); long Get32s(void * Long); unsigned long Get32u(void * Long); double ConvertAnyFormat(void * ValuePtr, int Format); bool ProcessExifDir(unsigned char * DirStart, unsigned char * OffsetBase, unsigned ExifLength, EXIFINFO * const pInfo, unsigned char ** const LastExifRefdP); int ExifImageWidth; int MotorolaOrder; Section_t Sections[MAX_SECTIONS]; int SectionsRead; bool freeinfo;};#endif//exif.cpp
/* * File:exif.cpp * Purpose:cpp EXIF reader * 16/Mar/2003 <ing.davide.pizzolato@libero.it> * based on jhead-1.8 by Matthias Wandel <mwandel(at)rim(dot)net> */#include "exif.h"////////////////////////////////////////////////////////////////////////////////Cexif::Cexif(EXIFINFO* info){if (info) {m_exifinfo = info;freeinfo = false;} else {m_exifinfo = new EXIFINFO;memset(m_exifinfo,0,sizeof(EXIFINFO));freeinfo = true;}m_szLastError[0]='\0';ExifImageWidth = MotorolaOrder = 0;SectionsRead=0;memset(&Sections, 0, MAX_SECTIONS * sizeof(Section_t));}////////////////////////////////////////////////////////////////////////////////Cexif::~Cexif(){for(int i=0;i<MAX_SECTIONS;i++) if(Sections[i].Data) free(Sections[i].Data);if (freeinfo) delete m_exifinfo;}////////////////////////////////////////////////////////////////////////////////bool Cexif::DecodeExif(FILE * hFile){ int a; int HaveCom = 0; a = fgetc(hFile); if (a != 0xff || fgetc(hFile) != M_SOI){ return 0; } for(;;){ int itemlen; int marker = 0; int ll,lh, got; unsigned char * Data; if (SectionsRead >= MAX_SECTIONS){strcpy(m_szLastError,"Too many sections in jpg file");return 0; } for (a=0;a<7;a++){ marker = fgetc(hFile); if (marker != 0xff) break; if (a >= 6){ printf("too many padding unsigned chars\n"); return 0; } } if (marker == 0xff){ // 0xff is legal padding, but if we get that many, something's wrong. strcpy(m_szLastError,"too many padding unsigned chars!");return 0; } Sections[SectionsRead].Type = marker; // Read the length of the section. lh = fgetc(hFile); ll = fgetc(hFile); itemlen = (lh << 8) | ll; if (itemlen < 2){ strcpy(m_szLastError,"invalid marker");return 0; } Sections[SectionsRead].Size = itemlen; Data = (unsigned char *)malloc(itemlen); if (Data == NULL){ strcpy(m_szLastError,"Could not allocate memory");return 0; } Sections[SectionsRead].Data = Data; // Store first two pre-read unsigned chars. Data[0] = (unsigned char)lh; Data[1] = (unsigned char)ll; got = (int)fread(Data+2, 1, itemlen-2,hFile); // Read the whole section. if (got != itemlen-2){ strcpy(m_szLastError,"Premature end of file?");return 0; } SectionsRead += 1; switch(marker){ case M_SOS: // stop before hitting compressed data // If reading entire image is requested, read the rest of the data. /*if (ReadMode & READ_IMAGE){ int cp, ep, size; // Determine how much file is left. cp = ftell(infile); fseek(infile, 0, SEEK_END); ep = ftell(infile); fseek(infile, cp, SEEK_SET); size = ep-cp; Data = (uchar *)malloc(size); if (Data == NULL){ strcpy(m_szLastError,"could not allocate data for entire image");return 0; } got = fread(Data, 1, size, infile); if (got != size){ strcpy(m_szLastError,"could not read the rest of the image");return 0; } Sections[SectionsRead].Data = Data; Sections[SectionsRead].Size = size; Sections[SectionsRead].Type = PSEUDO_IMAGE_MARKER; SectionsRead ++; HaveAll = 1; }*/ return 1; case M_EOI: // in case it's a tables-only JPEG stream printf("No image in jpeg!\n"); return 0; case M_COM: // Comment section if (HaveCom){ // Discard this section. free(Sections[--SectionsRead].Data);Sections[SectionsRead].Data=0; }else{ process_COM(Data, itemlen); HaveCom = 1; } break; case M_JFIF: // Regular jpegs always have this tag, exif images have the exif // marker instead, althogh ACDsee will write images with both markers. // this program will re-create this marker on absence of exif marker. // hence no need to keep the copy from the file. free(Sections[--SectionsRead].Data);Sections[SectionsRead].Data=0; break; case M_EXIF: // Seen files from some 'U-lead' software with Vivitar scanner // that uses marker 31 for non exif stuff. Thus make sure // it says 'Exif' in the section before treating it as exif. if (memcmp(Data+2, "Exif", 4) == 0){ m_exifinfo->IsExif = process_EXIF((unsigned char *)Data+2, itemlen); }else{ // Discard this section. free(Sections[--SectionsRead].Data);Sections[SectionsRead].Data=0; } break; case M_SOF0: case M_SOF1: case M_SOF2: case M_SOF3: case M_SOF5: case M_SOF6: case M_SOF7: case M_SOF9: case M_SOF10: case M_SOF11: case M_SOF13: case M_SOF14: case M_SOF15: process_SOFn(Data, marker); break; default: // Skip any other sections. //if (ShowTags) printf("Jpeg section marker 0x%02x size %d\n",marker, itemlen); break; } }return 1;}/////////////////////////////////////////////////////////////////////////////////*-------------------------------------------------------------------------- Process a EXIF marker Describes all the drivel that most digital cameras include...--------------------------------------------------------------------------*/bool Cexif::process_EXIF(unsigned char * CharBuf, unsigned int length){ m_exifinfo->FlashUsed = 0; /* If it's from a digicam, and it used flash, it says so. */ m_exifinfo->Comments[0] = '\0'; /* Initial value - null string */ ExifImageWidth = 0; { /* Check the EXIF header component */ static const unsigned char ExifHeader[] = "Exif\0\0"; if (memcmp(CharBuf+0, ExifHeader,6)){strcpy(m_szLastError,"Incorrect Exif header");return 0;} } if (memcmp(CharBuf+6,"II",2) == 0){ MotorolaOrder = 0; }else{ if (memcmp(CharBuf+6,"MM",2) == 0){ MotorolaOrder = 1; }else{ strcpy(m_szLastError,"Invalid Exif alignment marker.");return 0; } } /* Check the next two values for correctness. */ if (Get16u(CharBuf+8) != 0x2a){ strcpy(m_szLastError,"Invalid Exif start (1)");return 0; }int FirstOffset = Get32u(CharBuf+10); if (FirstOffset < 8 || FirstOffset > 16){ // I used to ensure this was set to 8 (website I used indicated its 8) // but PENTAX Optio 230 has it set differently, and uses it as offset. (Sept 11 2002) strcpy(m_szLastError,"Suspicious offset of first IFD value");return 0; } unsigned char * LastExifRefd = CharBuf; /* First directory starts 16 unsigned chars in. Offsets start at 8 unsigned chars in. */ if (!ProcessExifDir(CharBuf+14, CharBuf+6, length-6, m_exifinfo, &LastExifRefd))return 0; /* This is how far the interesting (non thumbnail) part of the exif went. */ // int ExifSettingsLength = LastExifRefd - CharBuf; /* Compute the CCD width, in milimeters. */ if (m_exifinfo->FocalplaneXRes != 0){ m_exifinfo->CCDWidth = (float)(ExifImageWidth * m_exifinfo->FocalplaneUnits / m_exifinfo->FocalplaneXRes); }return 1;}//--------------------------------------------------------------------------// Get 16 bits motorola order (always) for jpeg header stuff.//--------------------------------------------------------------------------int Cexif::Get16m(void * Short){ return (((unsigned char *)Short)[0] << 8) | ((unsigned char *)Short)[1];}/////////////////////////////////////////////////////////////////////////////////*-------------------------------------------------------------------------- Convert a 16 bit unsigned value from file's native unsigned char order--------------------------------------------------------------------------*/int Cexif::Get16u(void * Short){ if (MotorolaOrder){ return (((unsigned char *)Short)[0] << 8) | ((unsigned char *)Short)[1]; }else{ return (((unsigned char *)Short)[1] << 8) | ((unsigned char *)Short)[0]; }}/////////////////////////////////////////////////////////////////////////////////*-------------------------------------------------------------------------- Convert a 32 bit signed value from file's native unsigned char order--------------------------------------------------------------------------*/long Cexif::Get32s(void * Long){ if (MotorolaOrder){ return ((( char *)Long)[0] << 24) | (((unsigned char *)Long)[1] << 16) | (((unsigned char *)Long)[2] << 8 ) | (((unsigned char *)Long)[3] << 0 ); }else{ return ((( char *)Long)[3] << 24) | (((unsigned char *)Long)[2] << 16) | (((unsigned char *)Long)[1] << 8 ) | (((unsigned char *)Long)[0] << 0 ); }}/////////////////////////////////////////////////////////////////////////////////*-------------------------------------------------------------------------- Convert a 32 bit unsigned value from file's native unsigned char order--------------------------------------------------------------------------*/unsigned long Cexif::Get32u(void * Long){ return (unsigned long)Get32s(Long) & 0xffffffff;}/////////////////////////////////////////////////////////////////////////////////* Describes format descriptor */static const int BytesPerFormat[] = {0,1,1,2,4,8,1,1,2,4,8,4,8};#define NUM_FORMATS 12#define FMT_BYTE 1 #define FMT_STRING 2#define FMT_USHORT 3#define FMT_ULONG 4#define FMT_URATIONAL 5#define FMT_SBYTE 6#define FMT_UNDEFINED 7#define FMT_SSHORT 8#define FMT_SLONG 9#define FMT_SRATIONAL 10#define FMT_SINGLE 11#define FMT_DOUBLE 12/* Describes tag values */#define TAG_EXIF_VERSION 0x9000#define TAG_EXIF_OFFSET 0x8769#define TAG_INTEROP_OFFSET 0xa005#define TAG_MAKE 0x010F#define TAG_MODEL 0x0110#define TAG_ORIENTATION 0x0112#define TAG_XRESOLUTION 0x011A#define TAG_YRESOLUTION 0x011B#define TAG_RESOLUTIONUNIT 0x0128#define TAG_EXPOSURETIME 0x829A#define TAG_FNUMBER 0x829D#define TAG_SHUTTERSPEED 0x9201#define TAG_APERTURE 0x9202#define TAG_BRIGHTNESS 0x9203#define TAG_MAXAPERTURE 0x9205#define TAG_FOCALLENGTH 0x920A#define TAG_DATETIME_ORIGINAL 0x9003#define TAG_USERCOMMENT 0x9286#define TAG_SUBJECT_DISTANCE 0x9206#define TAG_FLASH 0x9209#define TAG_FOCALPLANEXRES 0xa20E#define TAG_FOCALPLANEYRES 0xa20F#define TAG_FOCALPLANEUNITS 0xa210#define TAG_EXIF_IMAGEWIDTH 0xA002#define TAG_EXIF_IMAGELENGTH 0xA003/* the following is added 05-jan-2001 vcs */#define TAG_EXPOSURE_BIAS 0x9204#define TAG_WHITEBALANCE 0x9208#define TAG_METERING_MODE 0x9207#define TAG_EXPOSURE_PROGRAM 0x8822#define TAG_ISO_EQUIVALENT 0x8827#define TAG_COMPRESSION_LEVEL 0x9102#define TAG_THUMBNAIL_OFFSET 0x0201#define TAG_THUMBNAIL_LENGTH 0x0202/*-------------------------------------------------------------------------- Process one of the nested EXIF directories.--------------------------------------------------------------------------*/bool Cexif::ProcessExifDir(unsigned char * DirStart, unsigned char * OffsetBase, unsigned ExifLength, EXIFINFO * const m_exifinfo, unsigned char ** const LastExifRefdP ){ int de; int a; int NumDirEntries; unsigned ThumbnailOffset = 0; unsigned ThumbnailSize = 0; NumDirEntries = Get16u(DirStart); if ((DirStart+2+NumDirEntries*12) > (OffsetBase+ExifLength)){ strcpy(m_szLastError,"Illegally sized directory");return 0; } for (de=0;de<NumDirEntries;de++){ int Tag, Format, Components; unsigned char * ValuePtr; /* This actually can point to a variety of things; it must be cast to other types when used. But we use it as a unsigned char-by-unsigned char cursor, so we declare it as a pointer to a generic unsigned char here. */ int BytesCount; unsigned char * DirEntry; DirEntry = DirStart+2+12*de; Tag = Get16u(DirEntry); Format = Get16u(DirEntry+2); Components = Get32u(DirEntry+4); if ((Format-1) >= NUM_FORMATS) { /* (-1) catches illegal zero case as unsigned underflows to positive large */ strcpy(m_szLastError,"Illegal format code in EXIF dir");return 0;} BytesCount = Components * BytesPerFormat[Format]; if (BytesCount > 4){ unsigned OffsetVal; OffsetVal = Get32u(DirEntry+8); /* If its bigger than 4 unsigned chars, the dir entry contains an offset.*/ if (OffsetVal+BytesCount > ExifLength){ /* Bogus pointer offset and / or unsigned charcount value */ strcpy(m_szLastError,"Illegal pointer offset value in EXIF.");return 0; } ValuePtr = OffsetBase+OffsetVal; }else{ /* 4 unsigned chars or less and value is in the dir entry itself */ ValuePtr = DirEntry+8; } if (*LastExifRefdP < ValuePtr+BytesCount){ /* Keep track of last unsigned char in the exif header that was actually referenced. That way, we know where the discardable thumbnail data begins. */ *LastExifRefdP = ValuePtr+BytesCount; } /* Extract useful components of tag */ switch(Tag){ case TAG_MAKE: strncpy(m_exifinfo->CameraMake, (char*)ValuePtr, 31); break; case TAG_MODEL: strncpy(m_exifinfo->CameraModel, (char*)ValuePtr, 39); break;case TAG_EXIF_VERSION:strncpy(m_exifinfo->Version,(char*)ValuePtr, 4);break; case TAG_DATETIME_ORIGINAL: strncpy(m_exifinfo->DateTime, (char*)ValuePtr, 19); break; case TAG_USERCOMMENT: // Olympus has this padded with trailing spaces. Remove these first. for (a=BytesCount;;){ a--; if (((char*)ValuePtr)[a] == ' '){ ((char*)ValuePtr)[a] = '\0'; }else{ break; } if (a == 0) break; } /* Copy the comment */ if (memcmp(ValuePtr, "ASCII",5) == 0){ for (a=5;a<10;a++){ char c; c = ((char*)ValuePtr)[a]; if (c != '\0' && c != ' '){ strncpy(m_exifinfo->Comments, (char*)ValuePtr+a, 199); break; } } }else{ strncpy(m_exifinfo->Comments, (char*)ValuePtr, 199); } break; case TAG_FNUMBER: /* Simplest way of expressing aperture, so I trust it the most. (overwrite previously computd value if there is one) */ m_exifinfo->ApertureFNumber = (float)ConvertAnyFormat(ValuePtr, Format); break; case TAG_APERTURE: case TAG_MAXAPERTURE: /* More relevant info always comes earlier, so only use this field if we don't have appropriate aperture information yet. */ if (m_exifinfo->ApertureFNumber == 0){ m_exifinfo->ApertureFNumber = (float)exp(ConvertAnyFormat(ValuePtr, Format)*log((float)2)*0.5); } break;case TAG_BRIGHTNESS:m_exifinfo->Brightness = (float)ConvertAnyFormat(ValuePtr, Format);break; case TAG_FOCALLENGTH: /* Nice digital cameras actually save the focal length as a function of how farthey are zoomed in. */ m_exifinfo->FocalLength = (float)ConvertAnyFormat(ValuePtr, Format); break; case TAG_SUBJECT_DISTANCE: /* Inidcates the distacne the autofocus camera is focused to. Tends to be less accurate as distance increases. */ m_exifinfo->Distance = (float)ConvertAnyFormat(ValuePtr, Format); break; case TAG_EXPOSURETIME: /* Simplest way of expressing exposure time, so I trust it most. (overwrite previously computd value if there is one) */ m_exifinfo->ExposureTime = (float)ConvertAnyFormat(ValuePtr, Format); break; case TAG_SHUTTERSPEED: /* More complicated way of expressing exposure time, so only use this value if we don't already have it from somewhere else. */ if (m_exifinfo->ExposureTime == 0){ m_exifinfo->ExposureTime = (float) (1/exp(ConvertAnyFormat(ValuePtr, Format)*log((float)2))); } break; case TAG_FLASH: if ((int)ConvertAnyFormat(ValuePtr, Format) & 7){ m_exifinfo->FlashUsed = 1; }else{ m_exifinfo->FlashUsed = 0; } break; case TAG_ORIENTATION: m_exifinfo->Orientation = (int)ConvertAnyFormat(ValuePtr, Format); if (m_exifinfo->Orientation < 1 || m_exifinfo->Orientation > 8){ strcpy(m_szLastError,"Undefined rotation value"); m_exifinfo->Orientation = 0; } break; case TAG_EXIF_IMAGELENGTH: case TAG_EXIF_IMAGEWIDTH: /* Use largest of height and width to deal with images that have been rotated to portrait format. */ a = (int)ConvertAnyFormat(ValuePtr, Format); if (ExifImageWidth < a) ExifImageWidth = a; break; case TAG_FOCALPLANEXRES: m_exifinfo->FocalplaneXRes = (float)ConvertAnyFormat(ValuePtr, Format); break; case TAG_FOCALPLANEYRES: m_exifinfo->FocalplaneYRes = (float)ConvertAnyFormat(ValuePtr, Format); break;case TAG_RESOLUTIONUNIT: switch((int)ConvertAnyFormat(ValuePtr, Format)){ case 1: m_exifinfo->ResolutionUnit = 1.0f; break; /* 1 inch */ case 2:m_exifinfo->ResolutionUnit = 1.0f; break; case 3: m_exifinfo->ResolutionUnit = 0.3937007874f; break; /* 1 centimeter*/ case 4: m_exifinfo->ResolutionUnit = 0.03937007874f; break; /* 1 millimeter*/ case 5: m_exifinfo->ResolutionUnit = 0.00003937007874f; /* 1 micrometer*/ } break; case TAG_FOCALPLANEUNITS: switch((int)ConvertAnyFormat(ValuePtr, Format)){ case 1: m_exifinfo->FocalplaneUnits = 1.0f; break; /* 1 inch */ case 2:m_exifinfo->FocalplaneUnits = 1.0f; break; case 3: m_exifinfo->FocalplaneUnits = 0.3937007874f; break; /* 1 centimeter*/ case 4: m_exifinfo->FocalplaneUnits = 0.03937007874f; break; /* 1 millimeter*/ case 5: m_exifinfo->FocalplaneUnits = 0.00003937007874f; /* 1 micrometer*/ } break; // Remaining cases contributed by: Volker C. Schoech <schoech(at)gmx(dot)de> case TAG_EXPOSURE_BIAS: m_exifinfo->ExposureBias = (float) ConvertAnyFormat(ValuePtr, Format); break; case TAG_WHITEBALANCE: m_exifinfo->Whitebalance = (int)ConvertAnyFormat(ValuePtr, Format); break; case TAG_METERING_MODE: m_exifinfo->MeteringMode = (int)ConvertAnyFormat(ValuePtr, Format); break; case TAG_EXPOSURE_PROGRAM: m_exifinfo->ExposureProgram = (int)ConvertAnyFormat(ValuePtr, Format); break; case TAG_ISO_EQUIVALENT: m_exifinfo->ISOequivalent = (int)ConvertAnyFormat(ValuePtr, Format); if ( m_exifinfo->ISOequivalent < 50 ) m_exifinfo->ISOequivalent *= 200; break; case TAG_COMPRESSION_LEVEL: m_exifinfo->CompressionLevel = (int)ConvertAnyFormat(ValuePtr, Format); break; case TAG_XRESOLUTION: m_exifinfo->Xresolution = (float)ConvertAnyFormat(ValuePtr, Format); break; case TAG_YRESOLUTION: m_exifinfo->Yresolution = (float)ConvertAnyFormat(ValuePtr, Format); break; case TAG_THUMBNAIL_OFFSET: ThumbnailOffset = (unsigned)ConvertAnyFormat(ValuePtr, Format); break; case TAG_THUMBNAIL_LENGTH: ThumbnailSize = (unsigned)ConvertAnyFormat(ValuePtr, Format); break; } if (Tag == TAG_EXIF_OFFSET || Tag == TAG_INTEROP_OFFSET){ unsigned char * SubdirStart; SubdirStart = OffsetBase + Get32u(ValuePtr); if (SubdirStart < OffsetBase || SubdirStart > OffsetBase+ExifLength){ strcpy(m_szLastError,"Illegal subdirectory link");return 0; } ProcessExifDir(SubdirStart, OffsetBase, ExifLength, m_exifinfo, LastExifRefdP); continue; } } { /* In addition to linking to subdirectories via exif tags, there's also a potential link to another directory at the end of each directory. This has got to be the result of a committee! */ unsigned char * SubdirStart; unsigned Offset; Offset = Get16u(DirStart+2+12*NumDirEntries); if (Offset){ SubdirStart = OffsetBase + Offset; if (SubdirStart < OffsetBase || SubdirStart > OffsetBase+ExifLength){ strcpy(m_szLastError,"Illegal subdirectory link");return 0; } ProcessExifDir(SubdirStart, OffsetBase, ExifLength, m_exifinfo, LastExifRefdP); } } if (ThumbnailSize && ThumbnailOffset){ if (ThumbnailSize + ThumbnailOffset <= ExifLength){ /* The thumbnail pointer appears to be valid. Store it. */ m_exifinfo->ThumbnailPointer = OffsetBase + ThumbnailOffset; m_exifinfo->ThumbnailSize = ThumbnailSize; } }return 1;}/////////////////////////////////////////////////////////////////////////////////*-------------------------------------------------------------------------- Evaluate number, be it int, rational, or float from directory.--------------------------------------------------------------------------*/double Cexif::ConvertAnyFormat(void * ValuePtr, int Format){ double Value; Value = 0; switch(Format){ case FMT_SBYTE: Value = *(signed char *)ValuePtr; break; case FMT_BYTE: Value = *(unsigned char *)ValuePtr; break; case FMT_USHORT: Value = Get16u(ValuePtr); break; case FMT_ULONG: Value = Get32u(ValuePtr); break; case FMT_URATIONAL: case FMT_SRATIONAL: { int Num,Den; Num = Get32s(ValuePtr); Den = Get32s(4+(char *)ValuePtr); if (Den == 0){ Value = 0; }else{ Value = (double)Num/Den; } break; } case FMT_SSHORT: Value = (signed short)Get16u(ValuePtr); break; case FMT_SLONG: Value = Get32s(ValuePtr); break; /* Not sure if this is correct (never seen float used in Exif format) */ case FMT_SINGLE: Value = (double)*(float *)ValuePtr; break; case FMT_DOUBLE: Value = *(double *)ValuePtr; break; } return Value;}////////////////////////////////////////////////////////////////////////////////void Cexif::process_COM (const unsigned char * Data, int length){ int ch; char Comment[MAX_COMMENT+1]; int nch; int a; nch = 0; if (length > MAX_COMMENT) length = MAX_COMMENT; // Truncate if it won't fit in our structure. for (a=2;a<length;a++){ ch = Data[a]; if (ch == '\r' && Data[a+1] == '\n') continue; // Remove cr followed by lf. if ((ch>=0x20) || ch == '\n' || ch == '\t'){ Comment[nch++] = (char)ch; }else{ Comment[nch++] = '?'; } } Comment[nch] = '\0'; // Null terminate //if (ShowTags) printf("COM marker comment: %s\n",Comment); strcpy(m_exifinfo->Comments,Comment);}////////////////////////////////////////////////////////////////////////////////void Cexif::process_SOFn (const unsigned char * Data, int marker){ int data_precision, num_components; data_precision = Data[2]; m_exifinfo->Height = Get16m((void*)(Data+3)); m_exifinfo->Width = Get16m((void*)(Data+5)); num_components = Data[7]; if (num_components == 3){ m_exifinfo->IsColor = 1; }else{ m_exifinfo->IsColor = 0; } m_exifinfo->Process = marker; //if (ShowTags) printf("JPEG image is %uw * %uh, %d color components, %d bits per sample\n", // ImageInfo.Width, ImageInfo.Height, num_components, data_precision);}//////////////////////////////////////////////////////////////////////////////////test.cpp
#include "exif.h"static EXIFINFO exif;void demo(void){ FILE* fp = fopen("D:\\test.jpg", "rb"); if (fp) { Cexif c(&exif); bool ok = c.DecodeExif(fp); fclose(fp); if (ok) { if ( exif.IsExif ) { printf("EXIF info:\n[%s]\n[%s]\n[%s]\n[%s]\n...\n", exif.Version, exif.CameraMake, exif.CameraModel, exif.DateTime); } else { printf("that isn't a EXIF format!\n"); } } else { printf("error! [%s]\n", c.m_szLastError); } } else { printf("can't found the file!\n"); }}int main(void){ demo(); getchar(); return 0;}相关参考链接：
http://libexif.sourceforge.net/
http://blog.csdn.net/lsiyun/article/details/5346754
http://blog.csdn.net/raptor/article/details/4882
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