Exif信息读取

#include <stdio.h> #include <algorithm> #include "exif.h" using std::string; namespace { // IF Entry struct IFEntry { // Raw fields unsigned short tag; unsigned short format; unsigned data; unsigned length; // Parsed fields string val_string; unsigned short val_16; unsigned val_32; double val_rational; unsigned char val_byte; }; // Helper functions unsigned int parse32(const unsigned char *buf, bool intel) { if (intel) return ((unsigned)buf[3]<<24) | ((unsigned)buf[2]<<16) | ((unsigned)buf[1]<<8) | buf[0]; return ((unsigned)buf[0]<<24) | ((unsigned)buf[1]<<16) | ((unsigned)buf[2]<<8) | buf[3]; } unsigned short parse16(const unsigned char *buf, bool intel) { if (intel) return ((unsigned) buf[1]<<8) | buf[0]; return ((unsigned) buf[0]<<8) | buf[1]; } string parseEXIFString(const unsigned char *buf, const unsigned num_components, const unsigned data, const unsigned base, const unsigned len) { string value; if (num_components <= 4) value.assign( (const char*)&data, num_components ); else { if (base+data+num_components <= len) value.assign( (const char*)(buf+base+data), num_components ); } return value; } double parseEXIFRational(const unsigned char *buf, bool intel) { double numerator = 0; double denominator = 1; numerator = (double) parse32(buf, intel); denominator= (double) parse32(buf+4, intel); if(denominator < 1e-20) return 0; return numerator/denominator; } IFEntry parseIFEntry(const unsigned char *buf, const unsigned offs, const bool alignIntel, const unsigned base, const unsigned len) { IFEntry result; // Each directory entry is composed of: // 2 bytes: tag number (data field) // 2 bytes: data format // 4 bytes: number of components // 4 bytes: data value or offset to data value result.tag = parse16(buf + offs, alignIntel); result.format = parse16(buf + offs + 2, alignIntel); result.length = parse32(buf + offs + 4, alignIntel); result.data = parse32(buf + offs + 8, alignIntel); // Parse value in specified format switch (result.format) { case 1: result.val_byte = (unsigned char) *(buf + offs + 8); break; case 2: result.val_string = parseEXIFString(buf, result.length, result.data, base, len); break; case 3: result.val_16 = parse16((const unsigned char *) buf + offs + 8, alignIntel); break; case 4: result.val_32 = result.data; break; case 5: if (base + result.data + 8 <= len) result.val_rational = parseEXIFRational(buf + base + result.data, alignIntel); break; case 7: case 9: case 10: break; default: result.tag = 0xFF; } return result; } } // // Locates the EXIF segment and parses it using parseFromEXIFSegment // int EXIFInfo::parseFrom(const unsigned char *buf, unsigned len) { if (!buf || len < 4) return PARSE_EXIF_ERROR_NO_EXIF; if (buf[0] != 0xFF || buf[1] != 0xD8) return PARSE_EXIF_ERROR_NO_JPEG; if (buf[len-2] != 0xFF || buf[len-1] != 0xD9) return PARSE_EXIF_ERROR_NO_JPEG; clear(); unsigned offs = 0; // current offset into buffer for (offs = 0; offs < len-1; offs++) if (buf[offs] == 0xFF && buf[offs+1] == 0xE1) break; if (offs + 4 > len) return PARSE_EXIF_ERROR_NO_EXIF; offs += 2; unsigned short section_length = parse16(buf + offs, false); if (offs + section_length > len || section_length < 16) return PARSE_EXIF_ERROR_CORRUPT; offs += 2; return parseFromEXIFSegment(buf + offs, len - offs); } int EXIFInfo::parseFrom(const string &data) { return parseFrom((const unsigned char *)data.data(), data.length()); } int EXIFInfo::parseFromEXIFSegment(const unsigned char *buf, unsigned len) { bool alignIntel = true; // byte alignment (defined in EXIF header) unsigned offs = 0; // current offset into buffer if (!buf || len < 6) return PARSE_EXIF_ERROR_NO_EXIF; if (!std::equal(buf, buf+6, "Exif\0\0")) return PARSE_EXIF_ERROR_NO_EXIF; offs += 6; if (offs + 8 > len) return PARSE_EXIF_ERROR_CORRUPT; unsigned tiff_header_start = offs; if (buf[offs] == 'I' && buf[offs+1] == 'I') alignIntel = true; else { if(buf[offs] == 'M' && buf[offs+1] == 'M') alignIntel = false; else return PARSE_EXIF_ERROR_UNKNOWN_BYTEALIGN; } this->ByteAlign = alignIntel; offs += 2; if (0x2a != parse16(buf+offs, alignIntel)) return PARSE_EXIF_ERROR_CORRUPT; offs += 2; unsigned first_ifd_offset = parse32(buf + offs, alignIntel); offs += first_ifd_offset - 4; if (offs >= len) return PARSE_EXIF_ERROR_CORRUPT; if (offs + 2 > len) return PARSE_EXIF_ERROR_CORRUPT; int num_entries = parse16(buf + offs, alignIntel); if (offs + 6 + 12 * num_entries > len) return PARSE_EXIF_ERROR_CORRUPT; offs += 2; unsigned exif_sub_ifd_offset = len; unsigned gps_sub_ifd_offset = len; while (--num_entries >= 0) { IFEntry result = parseIFEntry(buf, offs, alignIntel, tiff_header_start, len); offs += 12; switch(result.tag) { case 0x102: // Bits per sample if (result.format == 3) this->BitsPerSample = result.val_16; break; case 0x10E: // Image description if (result.format == 2) this->ImageDescription = result.val_string; break; case 0x10F: // Digicam make if (result.format == 2) this->Make = result.val_string; break; case 0x110: // Digicam model if (result.format == 2) this->Model = result.val_string; break; case 0x112: // Orientation of image if (result.format == 3) this->Orientation = result.val_16; break; case 0x131: // Software used for image if (result.format == 2) this->Software = result.val_string; break; case 0x132: // EXIF/TIFF date/time of image modification if (result.format == 2) this->DateTime = result.val_string; break; case 0x8298: // Copyright information if (result.format == 2) this->Copyright = result.val_string; break; case 0x8825: // GPS IFS offset gps_sub_ifd_offset = tiff_header_start + result.data; break; case 0x8769: // EXIF SubIFD offset exif_sub_ifd_offset = tiff_header_start + result.data; break; } } if (exif_sub_ifd_offset + 4 <= len) { offs = exif_sub_ifd_offset; int num_entries = parse16(buf + offs, alignIntel); if (offs + 6 + 12 * num_entries > len) return PARSE_EXIF_ERROR_CORRUPT; offs += 2; while (--num_entries >= 0) { IFEntry result = parseIFEntry(buf, offs, alignIntel, tiff_header_start, len); switch(result.tag) { case 0x829a: // Exposure time in seconds if (result.format == 5) this->ExposureTime = result.val_rational; break; case 0x829d: // FNumber if (result.format == 5) this->FNumber = result.val_rational; break; case 0x8827: // ISO Speed Rating if (result.format == 3) this->ISOSpeedRatings = result.val_16; break; case 0x9003: // Original date and time if (result.format == 2) this->DateTimeOriginal = result.val_string; break; case 0x9004: // Digit