//
// Main parsing function for an EXIF segment.
//
// PARAM: 'buf' start of the EXIF TIFF, which must be the bytes "Exif\0\0".
// PARAM: 'len' length of buffer
//
int easyexif::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;
// Now parsing the TIFF header. The first two bytes are either "II" or
// "MM" for Intel or Motorola byte alignment. Sanity check by parsing
// the unsigned short that follows, making sure it equals 0x2a. The
// last 4 bytes are an offset into the first IFD, which are added to
// the global offset counter. For this block, we expect the following
// minimum size:
// 2 bytes: 'II' or 'MM'
// 2 bytes: 0x002a
// 4 bytes: offset to first IDF
// -----------------------------
// 8 bytes
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 != parse_value<uint16_t>(buf+offs, alignIntel))
return PARSE_EXIF_ERROR_CORRUPT;
offs += 2;
unsigned first_ifd_offset = parse_value<uint32_t>(buf + offs, alignIntel);
offs += first_ifd_offset - 4;
if (offs >= len)
return PARSE_EXIF_ERROR_CORRUPT;
// Now parsing the first Image File Directory (IFD0, for the main image).
// An IFD consists of a variable number of 12-byte directory entries. The
// first two bytes of the IFD section contain the number of directory
// entries in the section. The last 4 bytes of the IFD contain an offset
// to the next IFD, which means this IFD must contain exactly 6 + 12 * num
// bytes of data.
if (offs + 2 > len)
return PARSE_EXIF_ERROR_CORRUPT;
int num_entries = parse_value<uint16_t>(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_short().front();
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_short().front();
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;
}
}
// Jump to the EXIF SubIFD if it exists and parse all the information
// there. Note that it's possible that the EXIF SubIFD doesn't exist.
// The EXIF SubIFD contains most of the interesting information that a
// typical user might want.
if (exif_sub_ifd_offset + 4 <= len) {
offs = exif_sub_ifd_offset;
int num_entries = parse_value<uint16_t>(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().front();
break;
case 0x829d:
// FNumber
if (result.format() == 5)
this->FNumber = result.val_rational().front();
break;
case 0x8827:
// ISO Speed Rating
if (result.format() == 3)
this->ISOSpeedRatings = result.val_short().front();
break;
case 0x9003:
// Original date and time
if (result.format() == 2)
this->DateTimeOriginal = result.val_string();
break;
case 0x9004:
// Digitization date and time
if (result.format() == 2)
this->DateTimeDigitized = result.val_string();
break;
case 0x9201:
// Shutter speed value
if (result.format() == 5)
this->ShutterSpeedValue = result.val_rational().front();
break;
case 0x9204:
// Exposure bias value
if (result.format() == 5)
this->ExposureBiasValue = result.val_rational().front();
break;
case 0x9206:
// Subject distance
if (result.format() == 5)
this->SubjectDistance = result.val_rational().front();
break;
case 0x9209:
// Flash used
if (result.format() == 3)
this->Flash = result.data() ? 1 : 0;
break;
case 0x920a:
// Focal length
if (result.format() == 5)
this->FocalLength = result.val_rational().front();
break;
case 0x9207:
// Metering mode
if (result.format() == 3)
this->MeteringMode = result.val_short().front();
break;
case 0x9291:
// Subsecond original time
if (result.format() == 2)
this->SubSecTimeOriginal = result.val_string();
break;
case 0xa002:
// EXIF Image width
if (result.format() == 4)
this->ImageWidth = result.val_long().front();
if (result.format() == 3)
this->ImageWidth = result.val_short().front();
break;
case 0xa003:
// EXIF Image height
if (result.format() == 4)
this->ImageHeight = result.val_long().front();
if (result.format() == 3)
this->ImageHeight = result.val_short().front();
break;
case 0xa405:
// Focal length in 35mm film
if (result.format() == 3)
this->FocalLengthIn35mm = result.val_short().front();
break;
case 0xa432:
if (result.format() == 5) {
this->LensInfo.FocalLengthMin = result.val_rational()[0];
this->LensInfo.FocalLengthMax = result.val_rational()[1];
this->LensInfo.FStopMin = result.val_rational()[2];
this->LensInfo.FStopMax = result.val_rational()[3];
}
break;
case 0xa433:
if (result.format() == 2) {
this->LensInfo.Make = result.val_string();
}
break;
case 0xa434:
if (result.format() == 2) {
this->LensInfo.Model = result.val_string();
}
break;
}
offs += 12;
}
}
// Jump to the GPS SubIFD if it exists and parse all the information
// there. Note that it's possible that the GPS SubIFD doesn't exist.
if (gps_sub_ifd_offset + 4 <= len) {
offs = gps_sub_ifd_offset;
int num_entries = parse_value<uint16_t>(buf + offs, alignIntel);
if (offs + 6 + 12 * num_entries > len)
return PARSE_EXIF_ERROR_CORRUPT;
offs += 2;
while (--num_entries >= 0) {
unsigned short tag, format;
unsigned length, data;
parseIFEntryHeader(buf + offs, alignIntel, tag, format, length, data);
switch(tag) {
case 1:
// GPS north or south
this->GeoLocation.LatComponents.direction = *(buf + offs + 8);
if ('S' == this->GeoLocation.LatComponents.direction)
this->GeoLocation.Latitude = -this->GeoLocation.Latitude;
break;
case 2:
// GPS latitude
if (format == 5 && length == 3) {
this->GeoLocation.LatComponents.degrees =
parse_value<Rational>(buf + data + tiff_header_start, alignIntel);
this->GeoLocation.LatComponents.minutes =
parse_value<Rational>(buf + data + tiff_header_start + 8, alignIntel);
this->GeoLocation.LatComponents.seconds =
parse_value<Rational>(buf + data + tiff_header_start + 16, alignIntel);
this->GeoLocation.Latitude =
this->GeoLocation.LatComponents.degrees +
this->GeoLocation.LatComponents.minutes / 60 +
this->GeoLocation.LatComponents.seconds / 3600;
if ('S' == this->GeoLocation.LatComponents.direction)
this->GeoLocation.Latitude = -this->GeoLocation.Latitude;
}
break;
case 3:
// GPS east or west
this->GeoLocation.LonComponents.direction = *(buf + offs + 8);
if ('W' == this->GeoLocation.LonComponents.direction)
this->GeoLocation.Longitude = -this->GeoLocation.Longitude;
break;
case 4:
// GPS longitude
if (format == 5 && length == 3) {
this->GeoLocation.LonComponents.degrees =
parse_value<Rational>(buf + data + tiff_header_start, alignIntel);
this->GeoLocation.LonComponents.minutes =
parse_value<Rational>(buf + data + tiff_header_start + 8, alignIntel);
this->GeoLocation.LonComponents.seconds =
parse_value<Rational>(buf + data + tiff_header_start + 16, alignIntel);
this->GeoLocation.Longitude =
this->GeoLocation.LonComponents.degrees +
this->GeoLocation.LonComponents.minutes / 60 +
this->GeoLocation.LonComponents.seconds / 3600;
if ('W' == this->GeoLocation.LonComponents.direction)
this->GeoLocation.Longitude = -this->GeoLocation.Longitude;
}
break;
case 5:
// GPS altitude reference (below or above sea level)
this->GeoLocation.AltitudeRef = *(buf + offs + 8);
if (1 == this->GeoLocation.AltitudeRef)
this->GeoLocation.Altitude = -this->GeoLocation.Altitude;
break;
case 6:
// GPS altitude reference
if (format == 5) {
this->GeoLocation.Altitude =
parse_value<Rational>(buf + data + tiff_header_start, alignIntel);
if (1 == this->GeoLocation.AltitudeRef)
this->GeoLocation.Altitude = -this->GeoLocation.Altitude;
}
break;
}
offs += 12;
}
}
return PARSE_EXIF_SUCCESS;
}
void readTag(IFEntry & result, easyexif::EXIFInfo * exif)
{
switch (result.tag()) {
case 0x102:
// Bits per sample
if (result.format() == 3)
exif->BitsPerSample = result.val_short().front();
break;
case 0x10E:
// Image description
if (result.format() == 2) exif->ImageDescription = result.val_string();
break;
case 0x10F:
// Digicam make
if (result.format() == 2) exif->Make = result.val_string();
break;
case 0x110:
// Digicam model
if (result.format() == 2) exif->Model = result.val_string();
break;
case 0x112:
// Orientation of image
if (result.format() == 3)
exif->Orientation = result.val_short().front();
break;
case 0x131:
// Software used for image
if (result.format() == 2) exif->Software = result.val_string();
break;
case 0x132:
// EXIF/TIFF date/time of image modification
if (result.format() == 2) exif->DateTime = result.val_string();
break;
case 0x8298:
// Copyright information
if (result.format() == 2) exif->Copyright = result.val_string();
break;
case 0x829a:
// Exposure time in seconds
if (result.format() == 5)
exif->ExposureTime = result.val_rational().front();
break;
case 0x829d:
// FNumber
if (result.format() == 5)
exif->FNumber = result.val_rational().front();
break;
case 0x8827:
// ISO Speed Rating
if (result.format() == 3)
exif->ISOSpeedRatings = result.val_short().front();
break;
case 0x9003:
// Original date and time
if (result.format() == 2)
exif->DateTimeOriginal = result.val_string();
break;
case 0x9004:
// Digitization date and time
if (result.format() == 2)
exif->DateTimeDigitized = result.val_string();
break;
case 0x9201:
// Shutter speed value
if (result.format() == 5)
exif->ShutterSpeedValue = result.val_rational().front();
break;
case 0x9204:
// Exposure bias value
if (result.format() == 5)
exif->ExposureBiasValue = result.val_rational().front();
break;
case 0x9206:
// Subject distance
if (result.format() == 5)
exif->SubjectDistance = result.val_rational().front();
break;
case 0x9209:
// Flash used
if (result.format() == 3) exif->Flash = result.data() ? 1 : 0;
break;
case 0x920a:
// Focal length
if (result.format() == 5)
exif->FocalLength = result.val_rational().front();
break;
case 0x9207:
// Metering mode
if (result.format() == 3)
exif->MeteringMode = result.val_short().front();
break;
case 0x9291:
// Subsecond original time
if (result.format() == 2)
exif->SubSecTimeOriginal = result.val_string();
break;
case 0xa002:
// EXIF Image width
if (result.format() == 4)
exif->ImageWidth = result.val_long().front();
if (result.format() == 3)
exif->ImageWidth = result.val_short().front();
break;
case 0xa003:
// EXIF Image height
if (result.format() == 4)
exif->ImageHeight = result.val_long().front();
if (result.format() == 3)
exif->ImageHeight = result.val_short().front();
break;
case 0xa20e:
// EXIF Focal plane X-resolution
if (result.format() == 5) {
exif->LensInfo.FocalPlaneXResolution = result.val_rational()[0];
}
break;
case 0xa20f:
// EXIF Focal plane Y-resolution
if (result.format() == 5) {
exif->LensInfo.FocalPlaneYResolution = result.val_rational()[0];
}
break;
case 0xa405:
// Focal length in 35mm film
if (result.format() == 3)
exif->FocalLengthIn35mm = result.val_short().front();
break;
case 0xa420:
if (result.format() == 2)
exif->ImageUniqueID = result.val_string();
break;
case 0xa432:
// Focal length and FStop.
if (result.format() == 5) {
exif->LensInfo.FocalLengthMin = result.val_rational()[0];
exif->LensInfo.FocalLengthMax = result.val_rational()[1];
exif->LensInfo.FStopMin = result.val_rational()[2];
exif->LensInfo.FStopMax = result.val_rational()[3];
}
break;
case 0xa433:
// Lens make.
if (result.format() == 2) {
exif->LensInfo.Make = result.val_string();
}
break;
case 0xa434:
// Lens model.
if (result.format() == 2) {
exif->LensInfo.Model = result.val_string();
}
break;
}
}