Merge pull request #612 from drewnoakes/fix-exif-thumbnail-offset

Fix Exif thumbnail offset

Source/com/drew/imaging/png/PngMetadataReader.java

@@ -330,7 +330,7 @@ private static void processChunk(@NotNull Metadata metadata, @NotNull PngChunk c
             metadata.addDirectory(directory);
         } else if (chunkType.equals(PngChunkType.eXIf)) {
             try {
-                ExifTiffHandler handler = new ExifTiffHandler(metadata, null);
+                ExifTiffHandler handler = new ExifTiffHandler(metadata, null, 0);
                 new TiffReader().processTiff(new ByteArrayReader(bytes), handler, 0);
             } catch (TiffProcessingException ex) {
                 PngDirectory directory = new PngDirectory(PngChunkType.eXIf);

Source/com/drew/imaging/tiff/TiffMetadataReader.java

@@ -67,7 +67,7 @@ public static Metadata readMetadata(@NotNull InputStream inputStream) throws IOE
     public static Metadata readMetadata(@NotNull RandomAccessReader reader) throws IOException, TiffProcessingException
     {
         Metadata metadata = new Metadata();
-        ExifTiffHandler handler = new ExifTiffHandler(metadata, null);
+        ExifTiffHandler handler = new ExifTiffHandler(metadata, null, 0);
         new TiffReader().processTiff(reader, handler, 0);
         return metadata;
     }

Source/com/drew/metadata/exif/ExifReader.java

@@ -87,7 +87,7 @@ public void extract(@NotNull final RandomAccessReader reader, @NotNull final Met
     /** Reads TIFF formatted Exif data at a specified offset within a {@link RandomAccessReader}. */
     public void extract(@NotNull final RandomAccessReader reader, @NotNull final Metadata metadata, int readerOffset, @Nullable Directory parentDirectory)
     {
-        ExifTiffHandler exifTiffHandler = new ExifTiffHandler(metadata, parentDirectory);
+        ExifTiffHandler exifTiffHandler = new ExifTiffHandler(metadata, parentDirectory, readerOffset);
 
         try {
             // Read the TIFF-formatted Exif data

Source/com/drew/metadata/exif/ExifThumbnailDescriptor.java

@@ -63,7 +63,8 @@ public String getThumbnailLengthDescription()
     @Nullable
     public String getThumbnailOffsetDescription()
     {
-        String value = _directory.getString(TAG_THUMBNAIL_OFFSET);
-        return value == null ? null : value + " bytes";
+        Integer offset = _directory.getAdjustedThumbnailOffset();
+
+        return offset == null ? null : offset.intValue() + " bytes";
     }
 }

Source/com/drew/metadata/exif/ExifThumbnailDirectory.java

@@ -34,7 +34,11 @@
 public class ExifThumbnailDirectory extends ExifDirectoryBase
 {
     /**
-     * The offset to thumbnail image bytes.
+     * The offset to thumbnail image bytes, relative to the start of the IFD.
+     *
+     * To obtain the offset relative to the start of the TIFF data stream, use
+     * <code>getAdjustedThumbnailOffset</code>, which includes the value of
+     * <code>getExifStartOffset</code>.
      */
     public static final int TAG_THUMBNAIL_OFFSET = 0x0201;
     /**
@@ -59,8 +63,11 @@ public class ExifThumbnailDirectory extends ExifDirectoryBase
         _tagNameMap.put(TAG_THUMBNAIL_LENGTH, "Thumbnail Length");
     }
 
-    public ExifThumbnailDirectory()
+    private final int _exifStartOffset;
+
+    public ExifThumbnailDirectory(int exifStartOffset)
     {
+        _exifStartOffset = exifStartOffset;
         this.setDescriptor(new ExifThumbnailDescriptor(this));
     }
 
@@ -77,4 +84,35 @@ protected HashMap<Integer, String> getTagNameMap()
     {
         return _tagNameMap;
     }
+
+    /**
+     * Gets the offset at which the Exif data stream commenced within any containing stream.
+     */
+    public int getExifStartOffset()
+    {
+        return _exifStartOffset;
+    }
+
+    /**
+     * Returns the offset to thumbnail data within the outermost data stream.
+     *
+     * The value for <code>TagThumbnailOffset</code> is relative to the Exif data stream.
+     * Generally, consumers of thumbnail data need this value relative to the outermost stream,
+     * so that the thumbnail data may be extracted from that stream.
+     *
+     * This property adds the value of <code>ExifStartOffset</code> to this tag's value in order
+     * to produce that value.
+     *
+     * Returns <code>null</code> when the tag is not defined in this directory.
+     */
+    public Integer getAdjustedThumbnailOffset()
+    {
+        Integer offset = this.getInteger(TAG_THUMBNAIL_OFFSET);
+
+        if (offset == null) {
+            return null;
+        }
+
+        return offset.intValue() + _exifStartOffset;
+    }
 }

Source/com/drew/metadata/exif/ExifTiffHandler.java

@@ -57,9 +57,12 @@
  */
 public class ExifTiffHandler extends DirectoryTiffHandler
 {
-    public ExifTiffHandler(@NotNull Metadata metadata, @Nullable Directory parentDirectory)
+    private final int _exifStartOffset;
+
+    public ExifTiffHandler(@NotNull Metadata metadata, @Nullable Directory parentDirectory, int exifStartOffset)
     {
         super(metadata, parentDirectory);
+        _exifStartOffset = exifStartOffset;
     }
 
     public void setTiffMarker(int marker) throws TiffProcessingException
@@ -149,7 +152,7 @@ public boolean hasFollowerIfd()
             if (_currentDirectory.containsTag(ExifDirectoryBase.TAG_PAGE_NUMBER))
                 pushDirectory(ExifImageDirectory.class);
             else
-                pushDirectory(ExifThumbnailDirectory.class);
+                pushDirectory(new ExifThumbnailDirectory(_exifStartOffset));
             return true;
         }
 

Source/com/drew/metadata/photoshop/PhotoshopTiffHandler.java

@@ -33,7 +33,7 @@ public class PhotoshopTiffHandler extends ExifTiffHandler
 
     public PhotoshopTiffHandler(Metadata metadata, Directory parentDirectory)
     {
-        super(metadata, parentDirectory);
+        super(metadata, parentDirectory, 0);
     }
 
     public boolean customProcessTag(final int tagOffset,

Source/com/drew/metadata/tiff/DirectoryTiffHandler.java

@@ -67,21 +67,26 @@ protected void pushDirectory(@NotNull Class<? extends Directory> directoryClass)
             throw new RuntimeException(e);
         }
 
+        pushDirectory(newDirectory);
+    }
+
+    protected void pushDirectory(@NotNull Directory directory)
+    {
         // If this is the first directory, don't add to the stack
         if (_currentDirectory == null) {
             // Apply any pending root parent to this new directory
             if (_rootParentDirectory != null) {
-                newDirectory.setParent(_rootParentDirectory);
+                directory.setParent(_rootParentDirectory);
                 _rootParentDirectory = null;
             }
         }
         else {
             // The current directory is pushed onto the stack, and set as the new directory's parent
             _directoryStack.push(_currentDirectory);
-            newDirectory.setParent(_currentDirectory);
+            directory.setParent(_currentDirectory);
         }
 
-        _currentDirectory = newDirectory;
+        _currentDirectory = directory;
         _metadata.addDirectory(_currentDirectory);
     }
 

Tests/com/drew/metadata/MetadataTest.java

@@ -96,7 +96,7 @@ public void testOrderOfDifferentTypes()
     {
         Metadata metadata = new Metadata();
         Directory directory1 = new ExifSubIFDDirectory();
-        Directory directory2 = new ExifThumbnailDirectory();
+        Directory directory2 = new ExifThumbnailDirectory(0);
         Directory directory3 = new ExifIFD0Directory();
 
         metadata.addDirectory(directory1);

Tests/com/drew/metadata/exif/ExifDirectoryTest.java

@@ -46,7 +46,7 @@ public void testGetDirectoryName() throws Exception
     {
         Directory subIFDDirectory = new ExifSubIFDDirectory();
         Directory ifd0Directory = new ExifIFD0Directory();
-        Directory thumbDirectory = new ExifThumbnailDirectory();
+        Directory thumbDirectory = new ExifThumbnailDirectory(0);
         Directory gpsDirectory = new GpsDirectory();
 
         assertFalse(subIFDDirectory.hasErrors());

Tests/com/drew/metadata/exif/ExifThumbnailDescriptorTest.java

@@ -36,7 +36,7 @@ public class ExifThumbnailDescriptorTest
     @Test
     public void testGetYCbCrSubsamplingDescription() throws Exception
     {
-        ExifThumbnailDirectory directory = new ExifThumbnailDirectory();
+        ExifThumbnailDirectory directory = new ExifThumbnailDirectory(0);
         directory.setIntArray(TAG_YCBCR_SUBSAMPLING, new int[]{2, 1});
 
         ExifThumbnailDescriptor descriptor = new ExifThumbnailDescriptor(directory);