1 package tim.prune.drew.jpeg;
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4 import java.util.HashMap;
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7 * Extracts Exif data from a JPEG header segment
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8 * Based on Drew Noakes' Metadata extractor at http://drewnoakes.com
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9 * which in turn is based on code from Jhead http://www.sentex.net/~mwandel/jhead/
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11 public class ExifReader
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13 /** The JPEG segment as an array of bytes */
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14 private final byte[] _data;
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17 * Represents the native byte ordering used in the JPEG segment. If true,
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18 * then we're using Motorola ordering (Big endian), else we're using Intel
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19 * ordering (Little endian).
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21 private boolean _isMotorolaByteOrder;
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23 /** Thumbnail offset */
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24 private int _thumbnailOffset = -1;
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25 /** Thumbnail length */
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26 private int _thumbnailLength = -1;
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28 /** The number of bytes used per format descriptor */
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29 private static final int[] BYTES_PER_FORMAT = {0, 1, 1, 2, 4, 8, 1, 1, 2, 4, 8, 4, 8};
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31 /** The number of formats known */
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32 private static final int MAX_FORMAT_CODE = 12;
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35 // Note: Cannot use the DataFormat enumeration in the case statement that uses these tags.
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36 // Is there a better way?
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37 //private static final int FMT_BYTE = 1;
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38 private static final int FMT_STRING = 2;
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39 //private static final int FMT_USHORT = 3;
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40 //private static final int FMT_ULONG = 4;
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41 private static final int FMT_URATIONAL = 5;
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42 //private static final int FMT_SBYTE = 6;
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43 //private static final int FMT_UNDEFINED = 7;
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44 //private static final int FMT_SSHORT = 8;
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45 //private static final int FMT_SLONG = 9;
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46 private static final int FMT_SRATIONAL = 10;
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47 //private static final int FMT_SINGLE = 11;
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48 //private static final int FMT_DOUBLE = 12;
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50 public static final int TAG_EXIF_OFFSET = 0x8769;
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51 public static final int TAG_INTEROP_OFFSET = 0xA005;
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52 public static final int TAG_GPS_INFO_OFFSET = 0x8825;
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53 public static final int TAG_MAKER_NOTE = 0x927C;
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55 public static final int TIFF_HEADER_START_OFFSET = 6;
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57 /** GPS tag version GPSVersionID 0 0 BYTE 4 */
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58 public static final int TAG_GPS_VERSION_ID = 0x0000;
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59 /** North or South Latitude GPSLatitudeRef 1 1 ASCII 2 */
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60 public static final int TAG_GPS_LATITUDE_REF = 0x0001;
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61 /** Latitude GPSLatitude 2 2 RATIONAL 3 */
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62 public static final int TAG_GPS_LATITUDE = 0x0002;
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63 /** East or West Longitude GPSLongitudeRef 3 3 ASCII 2 */
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64 public static final int TAG_GPS_LONGITUDE_REF = 0x0003;
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65 /** Longitude GPSLongitude 4 4 RATIONAL 3 */
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66 public static final int TAG_GPS_LONGITUDE = 0x0004;
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67 /** Altitude reference GPSAltitudeRef 5 5 BYTE 1 */
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68 public static final int TAG_GPS_ALTITUDE_REF = 0x0005;
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69 /** Altitude GPSAltitude 6 6 RATIONAL 1 */
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70 public static final int TAG_GPS_ALTITUDE = 0x0006;
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71 /** GPS time (atomic clock) GPSTimeStamp 7 7 RATIONAL 3 */
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72 public static final int TAG_GPS_TIMESTAMP = 0x0007;
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73 /** GPS date (atomic clock) GPSDateStamp 23 1d RATIONAL 3 */
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74 public static final int TAG_GPS_DATESTAMP = 0x001d;
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75 /** Exif timestamp */
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76 public static final int TAG_DATETIME_ORIGINAL = 0x9003;
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77 /** Thumbnail offset */
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78 private static final int TAG_THUMBNAIL_OFFSET = 0x0201;
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79 /** Thumbnail length */
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80 private static final int TAG_THUMBNAIL_LENGTH = 0x0202;
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84 * Creates an ExifReader for a Jpeg file
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85 * @param inFile File object to attempt to read from
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86 * @throws JpegException on failure
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88 public ExifReader(File inFile) throws JpegException
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90 JpegSegmentData segments = JpegSegmentReader.readSegments(inFile);
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91 _data = segments.getSegment(JpegSegmentReader.SEGMENT_APP1);
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95 * Performs the Exif data extraction
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96 * @return the GPS data found in the file
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98 public JpegData extract()
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100 JpegData metadata = new JpegData();
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104 // check for the header length
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105 if (_data.length<=14)
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107 metadata.addError("Exif data segment must contain at least 14 bytes");
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111 // check for the header preamble
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112 if (!"Exif\0\0".equals(new String(_data, 0, 6)))
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114 metadata.addError("Exif data segment doesn't begin with 'Exif'");
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118 // this should be either "MM" or "II"
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119 String byteOrderIdentifier = new String(_data, 6, 2);
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120 if (!setByteOrder(byteOrderIdentifier))
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122 metadata.addError("Unclear distinction between Motorola/Intel byte ordering: " + byteOrderIdentifier);
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126 // Check the next two values are 0x2A as expected
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127 if (get16Bits(8)!=0x2a)
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129 metadata.addError("Invalid Exif start - should have 0x2A at offset 8 in Exif header");
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133 int firstDirectoryOffset = get32Bits(10) + TIFF_HEADER_START_OFFSET;
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135 // Check that offset is within range
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136 if (firstDirectoryOffset>=_data.length - 1)
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138 metadata.addError("First exif directory offset is beyond end of Exif data segment");
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139 // First directory normally starts 14 bytes in -- try it here and catch another error in the worst case
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140 firstDirectoryOffset = 14;
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143 HashMap<Integer, String> processedDirectoryOffsets = new HashMap<Integer, String>();
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145 // 0th IFD (we merge with Exif IFD)
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146 processDirectory(metadata, false, processedDirectoryOffsets, firstDirectoryOffset, TIFF_HEADER_START_OFFSET);
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153 * Set the byte order identifier
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154 * @param byteOrderIdentifier String from exif
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155 * @return true if recognised, false otherwise
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157 private boolean setByteOrder(String byteOrderIdentifier)
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159 if ("MM".equals(byteOrderIdentifier)) {
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160 _isMotorolaByteOrder = true;
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161 } else if ("II".equals(byteOrderIdentifier)) {
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162 _isMotorolaByteOrder = false;
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171 * Recursive call to process one of the nested Tiff IFD directories.
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172 * 2 bytes: number of tags
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174 * 2 bytes: tag type
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175 * 2 bytes: format code
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176 * 4 bytes: component count
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178 private void processDirectory(JpegData inMetadata, boolean inIsGPS, HashMap<Integer, String> inDirectoryOffsets,
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179 int inDirOffset, int inTiffHeaderOffset)
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181 // check for directories we've already visited to avoid stack overflows when recursive/cyclic directory structures exist
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182 if (inDirectoryOffsets.containsKey(Integer.valueOf(inDirOffset)))
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185 // remember that we've visited this directory so that we don't visit it again later
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186 inDirectoryOffsets.put(Integer.valueOf(inDirOffset), "processed");
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188 if (inDirOffset >= _data.length || inDirOffset < 0)
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190 inMetadata.addError("Ignored directory marked to start outside data segment");
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194 // First two bytes in the IFD are the number of tags in this directory
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195 int dirTagCount = get16Bits(inDirOffset);
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196 // If no tags, exit without complaint
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197 if (dirTagCount == 0) return;
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199 if (!isDirectoryLengthValid(inDirOffset, inTiffHeaderOffset))
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201 inMetadata.addError("Directory length is not valid");
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205 inMetadata.setExifDataPresent();
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206 // Handle each tag in this directory
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207 for (int tagNumber = 0; tagNumber<dirTagCount; tagNumber++)
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209 final int tagOffset = calculateTagOffset(inDirOffset, tagNumber);
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211 // 2 bytes for the tag type
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212 final int tagType = get16Bits(tagOffset);
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214 // 2 bytes for the format code
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215 final int formatCode = get16Bits(tagOffset + 2);
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216 if (formatCode < 1 || formatCode > MAX_FORMAT_CODE)
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218 inMetadata.addError("Invalid format code: " + formatCode);
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222 // 4 bytes dictate the number of components in this tag's data
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223 final int componentCount = get32Bits(tagOffset + 4);
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224 if (componentCount < 0)
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226 inMetadata.addError("Negative component count in EXIF");
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229 // each component may have more than one byte... calculate the total number of bytes
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230 final int byteCount = componentCount * BYTES_PER_FORMAT[formatCode];
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231 final int tagValueOffset = calculateTagValueOffset(byteCount, tagOffset, inTiffHeaderOffset);
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232 if (tagValueOffset < 0 || tagValueOffset > _data.length)
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234 inMetadata.addError("Illegal pointer offset value in EXIF");
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238 // Check that this tag isn't going to allocate outside the bounds of the data array.
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239 // This addresses an uncommon OutOfMemoryError.
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240 if (byteCount < 0 || tagValueOffset + byteCount > _data.length)
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242 inMetadata.addError("Illegal number of bytes: " + byteCount);
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246 // Calculate the value as an offset for cases where the tag represents a directory
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247 final int subdirOffset = inTiffHeaderOffset + get32Bits(tagValueOffset);
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249 // Look in both basic Exif tags (for timestamp, thumbnail) and Gps tags (for lat, long, altitude, timestamp)
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252 case TAG_EXIF_OFFSET:
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253 processDirectory(inMetadata, false, inDirectoryOffsets, subdirOffset, inTiffHeaderOffset);
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255 case TAG_INTEROP_OFFSET:
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258 case TAG_GPS_INFO_OFFSET:
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259 processDirectory(inMetadata, true, inDirectoryOffsets, subdirOffset, inTiffHeaderOffset);
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261 case TAG_MAKER_NOTE:
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265 // not a known directory, so must just be a normal tag
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268 processGpsTag(inMetadata, tagType, tagValueOffset, componentCount, formatCode);
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272 processExifTag(inMetadata, tagType, tagValueOffset, componentCount, formatCode);
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278 // at the end of each IFD is an optional link to the next IFD
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279 final int finalTagOffset = calculateTagOffset(inDirOffset, dirTagCount);
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280 int nextDirectoryOffset = get32Bits(finalTagOffset);
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281 if (nextDirectoryOffset != 0)
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283 nextDirectoryOffset += inTiffHeaderOffset;
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284 if (nextDirectoryOffset>=_data.length)
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286 // Last 4 bytes of IFD reference another IFD with an address that is out of bounds
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289 else if (nextDirectoryOffset < inDirOffset)
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291 // Last 4 bytes of IFD reference another IFD with an address before the start of this directory
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294 // the next directory is of same type as this one
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295 processDirectory(inMetadata, false, inDirectoryOffsets, nextDirectoryOffset, inTiffHeaderOffset);
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301 * Check if the directory length is valid
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302 * @param dirStartOffset start offset for directory
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303 * @param tiffHeaderOffset Tiff header offeset
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304 * @return true if length is valid
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306 private boolean isDirectoryLengthValid(int inDirStartOffset, int inTiffHeaderOffset)
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308 int dirTagCount = get16Bits(inDirStartOffset);
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309 int dirLength = (2 + (12 * dirTagCount) + 4);
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310 if (dirLength + inDirStartOffset + inTiffHeaderOffset >= _data.length)
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312 // Note: Files that had thumbnails trimmed with jhead 1.3 or earlier might trigger this
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320 * Process a GPS tag and put the contents in the given metadata
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321 * @param inMetadata metadata holding extracted values
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322 * @param inTagType tag type (eg latitude)
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323 * @param inTagValueOffset start offset in data array
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324 * @param inComponentCount component count for tag
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325 * @param inFormatCode format code, eg byte
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327 private void processGpsTag(JpegData inMetadata, int inTagType, int inTagValueOffset,
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328 int inComponentCount, int inFormatCode)
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330 // Only interested in tags latref, lat, longref, lon, altref, alt and gps timestamp
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333 case TAG_GPS_LATITUDE_REF:
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334 inMetadata.setLatitudeRef(readString(inTagValueOffset, inFormatCode, inComponentCount));
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336 case TAG_GPS_LATITUDE:
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337 inMetadata.setLatitude(readRationalArray(inTagValueOffset, inFormatCode, inComponentCount));
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339 case TAG_GPS_LONGITUDE_REF:
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340 inMetadata.setLongitudeRef(readString(inTagValueOffset, inFormatCode, inComponentCount));
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342 case TAG_GPS_LONGITUDE:
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343 inMetadata.setLongitude(readRationalArray(inTagValueOffset, inFormatCode, inComponentCount));
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345 case TAG_GPS_ALTITUDE_REF:
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346 inMetadata.setAltitudeRef(_data[inTagValueOffset]);
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348 case TAG_GPS_ALTITUDE:
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349 inMetadata.setAltitude(readRational(inTagValueOffset, inFormatCode, inComponentCount));
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351 case TAG_GPS_TIMESTAMP:
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352 inMetadata.setGpsTimestamp(readRationalArray(inTagValueOffset, inFormatCode, inComponentCount));
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354 case TAG_GPS_DATESTAMP:
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355 inMetadata.setGpsDatestamp(readRationalArray(inTagValueOffset, inFormatCode, inComponentCount));
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357 default: // ignore all other tags
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363 * Process a general Exif tag
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364 * @param inMetadata metadata holding extracted values
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365 * @param inTagType tag type (eg latitude)
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366 * @param inTagValueOffset start offset in data array
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367 * @param inComponentCount component count for tag
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368 * @param inFormatCode format code, eg byte
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370 private void processExifTag(JpegData inMetadata, int inTagType, int inTagValueOffset,
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371 int inComponentCount, int inFormatCode)
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373 // Only interested in original timestamp, thumbnail offset and thumbnail length
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374 if (inTagType == TAG_DATETIME_ORIGINAL)
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376 inMetadata.setOriginalTimestamp(readString(inTagValueOffset, inFormatCode, inComponentCount));
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378 else if (inTagType == TAG_THUMBNAIL_OFFSET) {
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379 _thumbnailOffset = TIFF_HEADER_START_OFFSET + get16Bits(inTagValueOffset);
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380 extractThumbnail(inMetadata);
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382 else if (inTagType == TAG_THUMBNAIL_LENGTH) {
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383 _thumbnailLength = get16Bits(inTagValueOffset);
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384 extractThumbnail(inMetadata);
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389 * Attempt to extract the thumbnail image
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391 private void extractThumbnail(JpegData inMetadata)
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393 if (_thumbnailOffset > 0 && _thumbnailLength > 0 && inMetadata.getThumbnailImage() == null)
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395 byte[] thumbnailBytes = new byte[_thumbnailLength];
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396 System.arraycopy(_data, _thumbnailOffset, thumbnailBytes, 0, _thumbnailLength);
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397 inMetadata.setThumbnailImage(thumbnailBytes);
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403 * Calculate the tag value offset
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404 * @param inByteCount
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405 * @param inDirEntryOffset
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406 * @param inTiffHeaderOffset
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407 * @return new offset
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409 private int calculateTagValueOffset(int inByteCount, int inDirEntryOffset, int inTiffHeaderOffset)
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411 if (inByteCount > 4)
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413 // If it's bigger than 4 bytes, the dir entry contains an offset.
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414 // dirEntryOffset must be passed, as some makernote implementations (e.g. FujiFilm) incorrectly use an
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415 // offset relative to the start of the makernote itself, not the TIFF segment.
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416 final int offsetVal = get32Bits(inDirEntryOffset + 8);
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417 if (offsetVal + inByteCount > _data.length)
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419 // Bogus pointer offset and / or bytecount value
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420 return -1; // signal error
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422 return inTiffHeaderOffset + offsetVal;
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426 // 4 bytes or less and value is in the dir entry itself
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427 return inDirEntryOffset + 8;
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433 * Creates a String from the _data buffer starting at the specified offset,
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434 * and ending where byte=='\0' or where length==maxLength.
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435 * @param inOffset start offset
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436 * @param inFormatCode format code - should be string
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437 * @param inMaxLength max length of string
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438 * @return contents of tag, or null if format incorrect
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440 private String readString(int inOffset, int inFormatCode, int inMaxLength)
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442 if (inFormatCode != FMT_STRING) return null;
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443 // Calculate length
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445 while ((inOffset + length)<_data.length
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446 && _data[inOffset + length]!='\0'
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447 && length < inMaxLength)
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451 return new String(_data, inOffset, length);
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455 * Creates a Rational from the _data buffer starting at the specified offset
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456 * @param inOffset start offset
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457 * @param inFormatCode format code - should be srational or urational
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458 * @param inCount component count - should be 1
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459 * @return contents of tag as a Rational object
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461 private Rational readRational(int inOffset, int inFormatCode, int inCount)
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463 // Check the format is a single rational as expected
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464 if (inFormatCode != FMT_SRATIONAL && inFormatCode != FMT_URATIONAL
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465 || inCount != 1) return null;
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466 return new Rational(get32Bits(inOffset), get32Bits(inOffset + 4));
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471 * Creates a Rational array from the _data buffer starting at the specified offset
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472 * @param inOffset start offset
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473 * @param inFormatCode format code - should be srational or urational
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474 * @param inCount component count - number of components
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475 * @return contents of tag as an array of Rational objects
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477 private Rational[] readRationalArray(int inOffset, int inFormatCode, int inCount)
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479 // Check the format is rational as expected
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480 if (inFormatCode != FMT_SRATIONAL && inFormatCode != FMT_URATIONAL)
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482 // Build array of Rationals
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483 Rational[] answer = new Rational[inCount];
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484 for (int i=0; i<inCount; i++)
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485 answer[i] = new Rational(get32Bits(inOffset + (8 * i)), get32Bits(inOffset + 4 + (8 * i)));
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491 * Determine the offset at which a given InteropArray entry begins within the specified IFD.
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492 * @param dirStartOffset the offset at which the IFD starts
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493 * @param entryNumber the zero-based entry number
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495 private int calculateTagOffset(int dirStartOffset, int entryNumber)
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497 // add 2 bytes for the tag count
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498 // each entry is 12 bytes, so we skip 12 * the number seen so far
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499 return dirStartOffset + 2 + (12 * entryNumber);
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504 * Get a 16 bit value from file's native byte order. Between 0x0000 and 0xFFFF.
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506 private int get16Bits(int offset)
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508 if (offset<0 || offset+2>_data.length)
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509 throw new ArrayIndexOutOfBoundsException("attempt to read data outside of exif segment (index " + offset + " where max index is " + (_data.length - 1) + ")");
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511 if (_isMotorolaByteOrder) {
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512 // Motorola - MSB first
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513 return (_data[offset] << 8 & 0xFF00) | (_data[offset + 1] & 0xFF);
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515 // Intel ordering - LSB first
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516 return (_data[offset + 1] << 8 & 0xFF00) | (_data[offset] & 0xFF);
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522 * Get a 32 bit value from file's native byte order.
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524 private int get32Bits(int offset)
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526 if (offset < 0 || offset+4 > _data.length)
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527 throw new ArrayIndexOutOfBoundsException("attempt to read data outside of exif segment (index "
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528 + offset + " where max index is " + (_data.length - 1) + ")");
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530 if (_isMotorolaByteOrder)
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532 // Motorola - MSB first
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533 return (_data[offset] << 24 & 0xFF000000) |
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534 (_data[offset + 1] << 16 & 0xFF0000) |
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535 (_data[offset + 2] << 8 & 0xFF00) |
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536 (_data[offset + 3] & 0xFF);
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540 // Intel ordering - LSB first
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541 return (_data[offset + 3] << 24 & 0xFF000000) |
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542 (_data[offset + 2] << 16 & 0xFF0000) |
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543 (_data[offset + 1] << 8 & 0xFF00) |
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544 (_data[offset] & 0xFF);
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