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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29 * The number of bytes used per format descriptor.
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31 private static final int[] BYTES_PER_FORMAT = {0, 1, 1, 2, 4, 8, 1, 1, 2, 4, 8, 4, 8};
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34 * The number of formats known.
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36 private static final int MAX_FORMAT_CODE = 12;
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39 // Note: Cannot use the DataFormat enumeration in the case statement that uses these tags.
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40 // Is there a better way?
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41 private static final int FMT_BYTE = 1;
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42 private static final int FMT_STRING = 2;
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43 private static final int FMT_USHORT = 3;
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44 private static final int FMT_ULONG = 4;
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45 private static final int FMT_URATIONAL = 5;
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46 private static final int FMT_SBYTE = 6;
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47 private static final int FMT_UNDEFINED = 7;
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48 private static final int FMT_SSHORT = 8;
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49 private static final int FMT_SLONG = 9;
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50 private static final int FMT_SRATIONAL = 10;
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51 private static final int FMT_SINGLE = 11;
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52 private static final int FMT_DOUBLE = 12;
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54 public static final int TAG_EXIF_OFFSET = 0x8769;
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55 public static final int TAG_INTEROP_OFFSET = 0xA005;
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56 public static final int TAG_GPS_INFO_OFFSET = 0x8825;
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57 public static final int TAG_MAKER_NOTE = 0x927C;
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59 public static final int TIFF_HEADER_START_OFFSET = 6;
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61 /** GPS tag version GPSVersionID 0 0 BYTE 4 */
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62 public static final int TAG_GPS_VERSION_ID = 0x0000;
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63 /** North or South Latitude GPSLatitudeRef 1 1 ASCII 2 */
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64 public static final int TAG_GPS_LATITUDE_REF = 0x0001;
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65 /** Latitude GPSLatitude 2 2 RATIONAL 3 */
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66 public static final int TAG_GPS_LATITUDE = 0x0002;
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67 /** East or West Longitude GPSLongitudeRef 3 3 ASCII 2 */
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68 public static final int TAG_GPS_LONGITUDE_REF = 0x0003;
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69 /** Longitude GPSLongitude 4 4 RATIONAL 3 */
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70 public static final int TAG_GPS_LONGITUDE = 0x0004;
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71 /** Altitude reference GPSAltitudeRef 5 5 BYTE 1 */
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72 public static final int TAG_GPS_ALTITUDE_REF = 0x0005;
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73 /** Altitude GPSAltitude 6 6 RATIONAL 1 */
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74 public static final int TAG_GPS_ALTITUDE = 0x0006;
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75 /** GPS time (atomic clock) GPSTimeStamp 7 7 RATIONAL 3 */
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76 public static final int TAG_GPS_TIMESTAMP = 0x0007;
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77 /** GPS date (atomic clock) GPSDateStamp 23 1d RATIONAL 3 */
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78 public static final int TAG_GPS_DATESTAMP = 0x001d;
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79 /** Exif timestamp */
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80 public static final int TAG_DATETIME_ORIGINAL = 0x9003;
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81 /** Thumbnail offset */
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82 private static final int TAG_THUMBNAIL_OFFSET = 0x0201;
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83 /** Thumbnail length */
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84 private static final int TAG_THUMBNAIL_LENGTH = 0x0202;
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88 * Creates an ExifReader for a Jpeg file.
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89 * @param inFile File object to attempt to read from
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90 * @throws JpegException on failure
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92 public ExifReader(File inFile) throws JpegException
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94 JpegSegmentData segments = JpegSegmentReader.readSegments(inFile);
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95 _data = segments.getSegment(JpegSegmentReader.SEGMENT_APP1);
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99 * Performs the Exif data extraction
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100 * @return the GPS data found in the file
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102 public JpegData extract()
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104 JpegData metadata = new JpegData();
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108 // check for the header length
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109 if (_data.length<=14)
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111 metadata.addError("Exif data segment must contain at least 14 bytes");
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115 // check for the header preamble
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116 if (!"Exif\0\0".equals(new String(_data, 0, 6)))
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118 metadata.addError("Exif data segment doesn't begin with 'Exif'");
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122 // this should be either "MM" or "II"
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123 String byteOrderIdentifier = new String(_data, 6, 2);
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124 if (!setByteOrder(byteOrderIdentifier))
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126 metadata.addError("Unclear distinction between Motorola/Intel byte ordering: " + byteOrderIdentifier);
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130 // Check the next two values are 0x2A as expected
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131 if (get16Bits(8)!=0x2a)
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133 metadata.addError("Invalid Exif start - should have 0x2A at offset 8 in Exif header");
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137 int firstDirectoryOffset = get32Bits(10) + TIFF_HEADER_START_OFFSET;
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139 // Check that offset is within range
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140 if (firstDirectoryOffset>=_data.length - 1)
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142 metadata.addError("First exif directory offset is beyond end of Exif data segment");
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143 // First directory normally starts 14 bytes in -- try it here and catch another error in the worst case
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144 firstDirectoryOffset = 14;
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147 HashMap processedDirectoryOffsets = new HashMap();
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149 // 0th IFD (we merge with Exif IFD)
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150 processDirectory(metadata, false, processedDirectoryOffsets, firstDirectoryOffset, TIFF_HEADER_START_OFFSET);
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157 * Set the byte order identifier
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158 * @param byteOrderIdentifier String from exif
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159 * @return true if recognised, false otherwise
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161 private boolean setByteOrder(String byteOrderIdentifier)
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163 if ("MM".equals(byteOrderIdentifier)) {
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164 _isMotorolaByteOrder = true;
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165 } else if ("II".equals(byteOrderIdentifier)) {
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166 _isMotorolaByteOrder = false;
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175 * Recursive call to process one of the nested Tiff IFD directories.
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176 * 2 bytes: number of tags
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178 * 2 bytes: tag type
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179 * 2 bytes: format code
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180 * 4 bytes: component count
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182 private void processDirectory(JpegData inMetadata, boolean inIsGPS, HashMap inDirectoryOffsets,
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183 int inDirOffset, int inTiffHeaderOffset)
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185 // check for directories we've already visited to avoid stack overflows when recursive/cyclic directory structures exist
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186 if (inDirectoryOffsets.containsKey(new Integer(inDirOffset)))
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189 // remember that we've visited this directory so that we don't visit it again later
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190 inDirectoryOffsets.put(new Integer(inDirOffset), "processed");
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192 if (inDirOffset >= _data.length || inDirOffset < 0)
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194 inMetadata.addError("Ignored directory marked to start outside data segment");
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198 // First two bytes in the IFD are the number of tags in this directory
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199 int dirTagCount = get16Bits(inDirOffset);
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200 // If no tags, exit without complaint
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201 if (dirTagCount == 0) return;
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203 if (!isDirectoryLengthValid(inDirOffset, inTiffHeaderOffset))
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205 inMetadata.addError("Directory length is not valid");
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209 inMetadata.setExifDataPresent();
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210 // Handle each tag in this directory
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211 for (int tagNumber = 0; tagNumber<dirTagCount; tagNumber++)
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213 final int tagOffset = calculateTagOffset(inDirOffset, tagNumber);
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215 // 2 bytes for the tag type
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216 final int tagType = get16Bits(tagOffset);
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218 // 2 bytes for the format code
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219 final int formatCode = get16Bits(tagOffset + 2);
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220 if (formatCode < 1 || formatCode > MAX_FORMAT_CODE)
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222 inMetadata.addError("Invalid format code: " + formatCode);
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226 // 4 bytes dictate the number of components in this tag's data
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227 final int componentCount = get32Bits(tagOffset + 4);
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228 if (componentCount < 0)
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230 inMetadata.addError("Negative component count in EXIF");
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233 // each component may have more than one byte... calculate the total number of bytes
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234 final int byteCount = componentCount * BYTES_PER_FORMAT[formatCode];
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235 final int tagValueOffset = calculateTagValueOffset(byteCount, tagOffset, inTiffHeaderOffset);
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236 if (tagValueOffset < 0 || tagValueOffset > _data.length)
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238 inMetadata.addError("Illegal pointer offset value in EXIF");
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242 // Check that this tag isn't going to allocate outside the bounds of the data array.
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243 // This addresses an uncommon OutOfMemoryError.
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244 if (byteCount < 0 || tagValueOffset + byteCount > _data.length)
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246 inMetadata.addError("Illegal number of bytes: " + byteCount);
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250 // Calculate the value as an offset for cases where the tag represents a directory
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251 final int subdirOffset = inTiffHeaderOffset + get32Bits(tagValueOffset);
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253 // Look in both basic Exif tags (for timestamp, thumbnail) and Gps tags (for lat, long, altitude, timestamp)
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256 case TAG_EXIF_OFFSET:
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257 processDirectory(inMetadata, false, inDirectoryOffsets, subdirOffset, inTiffHeaderOffset);
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259 case TAG_INTEROP_OFFSET:
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262 case TAG_GPS_INFO_OFFSET:
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263 processDirectory(inMetadata, true, inDirectoryOffsets, subdirOffset, inTiffHeaderOffset);
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265 case TAG_MAKER_NOTE:
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269 // not a known directory, so must just be a normal tag
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272 processGpsTag(inMetadata, tagType, tagValueOffset, componentCount, formatCode);
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276 processExifTag(inMetadata, tagType, tagValueOffset, componentCount, formatCode);
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282 // at the end of each IFD is an optional link to the next IFD
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283 final int finalTagOffset = calculateTagOffset(inDirOffset, dirTagCount);
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284 int nextDirectoryOffset = get32Bits(finalTagOffset);
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285 if (nextDirectoryOffset != 0)
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287 nextDirectoryOffset += inTiffHeaderOffset;
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288 if (nextDirectoryOffset>=_data.length)
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290 // Last 4 bytes of IFD reference another IFD with an address that is out of bounds
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293 else if (nextDirectoryOffset < inDirOffset)
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295 // Last 4 bytes of IFD reference another IFD with an address before the start of this directory
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298 // the next directory is of same type as this one
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299 processDirectory(inMetadata, false, inDirectoryOffsets, nextDirectoryOffset, inTiffHeaderOffset);
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305 * Check if the directory length is valid
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306 * @param dirStartOffset start offset for directory
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307 * @param tiffHeaderOffset Tiff header offeset
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308 * @return true if length is valid
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310 private boolean isDirectoryLengthValid(int inDirStartOffset, int inTiffHeaderOffset)
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312 int dirTagCount = get16Bits(inDirStartOffset);
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313 int dirLength = (2 + (12 * dirTagCount) + 4);
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314 if (dirLength + inDirStartOffset + inTiffHeaderOffset >= _data.length)
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316 // Note: Files that had thumbnails trimmed with jhead 1.3 or earlier might trigger this
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324 * Process a GPS tag and put the contents in the given metadata
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325 * @param inMetadata metadata holding extracted values
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326 * @param inTagType tag type (eg latitude)
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327 * @param inTagValueOffset start offset in data array
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328 * @param inComponentCount component count for tag
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329 * @param inFormatCode format code, eg byte
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331 private void processGpsTag(JpegData inMetadata, int inTagType, int inTagValueOffset,
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332 int inComponentCount, int inFormatCode)
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334 // Only interested in tags latref, lat, longref, lon, altref, alt and gps timestamp
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337 case TAG_GPS_LATITUDE_REF:
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338 inMetadata.setLatitudeRef(readString(inTagValueOffset, inFormatCode, inComponentCount));
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340 case TAG_GPS_LATITUDE:
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341 inMetadata.setLatitude(readRationalArray(inTagValueOffset, inFormatCode, inComponentCount));
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343 case TAG_GPS_LONGITUDE_REF:
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344 inMetadata.setLongitudeRef(readString(inTagValueOffset, inFormatCode, inComponentCount));
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346 case TAG_GPS_LONGITUDE:
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347 inMetadata.setLongitude(readRationalArray(inTagValueOffset, inFormatCode, inComponentCount));
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349 case TAG_GPS_ALTITUDE_REF:
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350 inMetadata.setAltitudeRef(_data[inTagValueOffset]);
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352 case TAG_GPS_ALTITUDE:
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353 inMetadata.setAltitude(readRational(inTagValueOffset, inFormatCode, inComponentCount));
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355 case TAG_GPS_TIMESTAMP:
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356 inMetadata.setGpsTimestamp(readRationalArray(inTagValueOffset, inFormatCode, inComponentCount));
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358 case TAG_GPS_DATESTAMP:
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359 inMetadata.setGpsDatestamp(readRationalArray(inTagValueOffset, inFormatCode, inComponentCount));
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361 default: // ignore all other tags
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367 * Process a general Exif tag
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368 * @param inMetadata metadata holding extracted values
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369 * @param inTagType tag type (eg latitude)
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370 * @param inTagValueOffset start offset in data array
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371 * @param inComponentCount component count for tag
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372 * @param inFormatCode format code, eg byte
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374 private void processExifTag(JpegData inMetadata, int inTagType, int inTagValueOffset,
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375 int inComponentCount, int inFormatCode)
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377 // Only interested in original timestamp, thumbnail offset and thumbnail length
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378 if (inTagType == TAG_DATETIME_ORIGINAL)
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380 inMetadata.setOriginalTimestamp(readString(inTagValueOffset, inFormatCode, inComponentCount));
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382 else if (inTagType == TAG_THUMBNAIL_OFFSET) {
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383 _thumbnailOffset = TIFF_HEADER_START_OFFSET + get16Bits(inTagValueOffset);
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384 extractThumbnail(inMetadata);
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386 else if (inTagType == TAG_THUMBNAIL_LENGTH) {
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387 _thumbnailLength = get16Bits(inTagValueOffset);
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388 extractThumbnail(inMetadata);
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393 * Attempt to extract the thumbnail image
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395 private void extractThumbnail(JpegData inMetadata)
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397 if (_thumbnailOffset > 0 && _thumbnailLength > 0 && inMetadata.getThumbnailImage() == null)
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399 byte[] thumbnailBytes = new byte[_thumbnailLength];
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400 System.arraycopy(_data, _thumbnailOffset, thumbnailBytes, 0, _thumbnailLength);
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401 inMetadata.setThumbnailImage(thumbnailBytes);
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407 * Calculate the tag value offset
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408 * @param inByteCount
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409 * @param inDirEntryOffset
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410 * @param inTiffHeaderOffset
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411 * @return new offset
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413 private int calculateTagValueOffset(int inByteCount, int inDirEntryOffset, int inTiffHeaderOffset)
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415 if (inByteCount > 4)
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417 // If it's bigger than 4 bytes, the dir entry contains an offset.
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418 // dirEntryOffset must be passed, as some makernote implementations (e.g. FujiFilm) incorrectly use an
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419 // offset relative to the start of the makernote itself, not the TIFF segment.
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420 final int offsetVal = get32Bits(inDirEntryOffset + 8);
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421 if (offsetVal + inByteCount > _data.length)
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423 // Bogus pointer offset and / or bytecount value
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424 return -1; // signal error
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426 return inTiffHeaderOffset + offsetVal;
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430 // 4 bytes or less and value is in the dir entry itself
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431 return inDirEntryOffset + 8;
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437 * Creates a String from the _data buffer starting at the specified offset,
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438 * and ending where byte=='\0' or where length==maxLength.
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439 * @param inOffset start offset
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440 * @param inFormatCode format code - should be string
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441 * @param inMaxLength max length of string
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442 * @return contents of tag, or null if format incorrect
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444 private String readString(int inOffset, int inFormatCode, int inMaxLength)
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446 if (inFormatCode != FMT_STRING) return null;
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447 // Calculate length
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449 while ((inOffset + length)<_data.length
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450 && _data[inOffset + length]!='\0'
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451 && length < inMaxLength)
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455 return new String(_data, inOffset, length);
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459 * Creates a Rational from the _data buffer starting at the specified offset
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460 * @param inOffset start offset
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461 * @param inFormatCode format code - should be srational or urational
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462 * @param inCount component count - should be 1
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463 * @return contents of tag as a Rational object
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465 private Rational readRational(int inOffset, int inFormatCode, int inCount)
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467 // Check the format is a single rational as expected
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468 if (inFormatCode != FMT_SRATIONAL && inFormatCode != FMT_URATIONAL
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469 || inCount != 1) return null;
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470 return new Rational(get32Bits(inOffset), get32Bits(inOffset + 4));
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475 * Creates a Rational array from the _data buffer starting at the specified offset
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476 * @param inOffset start offset
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477 * @param inFormatCode format code - should be srational or urational
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478 * @param inCount component count - number of components
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479 * @return contents of tag as an array of Rational objects
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481 private Rational[] readRationalArray(int inOffset, int inFormatCode, int inCount)
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483 // Check the format is rational as expected
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484 if (inFormatCode != FMT_SRATIONAL && inFormatCode != FMT_URATIONAL)
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486 // Build array of Rationals
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487 Rational[] answer = new Rational[inCount];
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488 for (int i=0; i<inCount; i++)
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489 answer[i] = new Rational(get32Bits(inOffset + (8 * i)), get32Bits(inOffset + 4 + (8 * i)));
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495 * Determine the offset at which a given InteropArray entry begins within the specified IFD.
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496 * @param dirStartOffset the offset at which the IFD starts
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497 * @param entryNumber the zero-based entry number
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499 private int calculateTagOffset(int dirStartOffset, int entryNumber)
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501 // add 2 bytes for the tag count
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502 // each entry is 12 bytes, so we skip 12 * the number seen so far
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503 return dirStartOffset + 2 + (12 * entryNumber);
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508 * Get a 16 bit value from file's native byte order. Between 0x0000 and 0xFFFF.
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510 private int get16Bits(int offset)
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512 if (offset<0 || offset+2>_data.length)
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513 throw new ArrayIndexOutOfBoundsException("attempt to read data outside of exif segment (index " + offset + " where max index is " + (_data.length - 1) + ")");
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515 if (_isMotorolaByteOrder) {
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516 // Motorola - MSB first
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517 return (_data[offset] << 8 & 0xFF00) | (_data[offset + 1] & 0xFF);
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519 // Intel ordering - LSB first
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520 return (_data[offset + 1] << 8 & 0xFF00) | (_data[offset] & 0xFF);
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526 * Get a 32 bit value from file's native byte order.
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528 private int get32Bits(int offset)
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530 if (offset < 0 || offset+4 > _data.length)
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531 throw new ArrayIndexOutOfBoundsException("attempt to read data outside of exif segment (index "
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532 + offset + " where max index is " + (_data.length - 1) + ")");
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534 if (_isMotorolaByteOrder)
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536 // Motorola - MSB first
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537 return (_data[offset] << 24 & 0xFF000000) |
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538 (_data[offset + 1] << 16 & 0xFF0000) |
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539 (_data[offset + 2] << 8 & 0xFF00) |
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540 (_data[offset + 3] & 0xFF);
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544 // Intel ordering - LSB first
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545 return (_data[offset + 3] << 24 & 0xFF000000) |
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546 (_data[offset + 2] << 16 & 0xFF0000) |
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547 (_data[offset + 1] << 8 & 0xFF00) |
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548 (_data[offset] & 0xFF);
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