- Defined additional JPEG segment types: DNL, DRI, DHP and EXP

- Removed the requirement in HuffmanTablesDirectory.isTypical() that the number of Huffman tables must be 4 to accommodate progressive JPEGs
- Made JpegDhtReader handle stuffing bytes in Huffman tables
- Created JpegDnlReader for DNL segment support

Source/com/drew/imaging/jpeg/JpegMetadataReader.java

@@ -33,6 +33,7 @@
 import com.drew.metadata.jfxx.JfxxReader;
 import com.drew.metadata.jpeg.JpegCommentReader;
 import com.drew.metadata.jpeg.JpegDhtReader;
+import com.drew.metadata.jpeg.JpegDnlReader;
 import com.drew.metadata.jpeg.JpegReader;
 import com.drew.metadata.photoshop.DuckyReader;
 import com.drew.metadata.photoshop.PhotoshopReader;
@@ -65,7 +66,8 @@ public class JpegMetadataReader
             new DuckyReader(),
             new IptcReader(),
             new AdobeJpegReader(),
-            new JpegDhtReader()
+            new JpegDhtReader(),
+            new JpegDnlReader()
     );
 
     @NotNull

Source/com/drew/imaging/jpeg/JpegSegmentType.java

@@ -92,6 +92,18 @@ public enum JpegSegmentType
     /** Define Quantization Table segment identifier. */
     DQT((byte)0xDB, false),
 
+    /** Define Number of Lines segment identifier. */
+    DNL((byte)0xDC, false),
+
+    /** Define Restart Interval segment identifier. */
+    DRI((byte)0xDD, false),
+
+    /** Define Hierarchical Progression segment identifier. */
+    DHP((byte)0xDE, false),
+
+    /** EXPand reference component(s) segment identifier. */
+    EXP((byte)0xDF, false),
+
     /** Define Huffman Table segment identifier. */
     DHT((byte)0xC4, false),
 

Source/com/drew/metadata/jpeg/HuffmanTablesDirectory.java

@@ -200,7 +200,7 @@ protected List<HuffmanTable> getTables() {
      *         Huffman tables.
      */
     public boolean isTypical() {
-        if (tables.size() != 4) {
+        if (tables.size() == 0) {
             return false;
         }
         for (HuffmanTable table : tables) {

Source/com/drew/metadata/jpeg/JpegDhtReader.java

@@ -69,12 +69,12 @@ public void extract(@NotNull final SequentialReader reader, @NotNull final Metad
                 HuffmanTableClass tableClass = HuffmanTableClass.typeOf((header & 0xF0) >> 4);
                 int tableDestinationId = header & 0xF;
 
-                byte[] lBytes = reader.getBytes(16);
+                byte[] lBytes = getBytes(reader, 16);
                 int vCount = 0;
                 for (byte b : lBytes) {
                     vCount += b;
                 }
-                byte[] vBytes = reader.getBytes(vCount);
+                byte[] vBytes = getBytes(reader, vCount);
                 directory.getTables().add(new HuffmanTable(tableClass, tableDestinationId, lBytes, vBytes));
             }
         } catch (IOException me) {
@@ -83,4 +83,19 @@ public void extract(@NotNull final SequentialReader reader, @NotNull final Metad
 
         directory.setInt(HuffmanTablesDirectory.TAG_NUMBER_OF_TABLES, directory.getTables().size());
     }
+
+    private byte[] getBytes(@NotNull final SequentialReader reader, int count) throws IOException {
+        byte[] bytes = new byte[count];
+        for (int i = 0; i < count; i++) {
+            byte b = reader.getByte();
+            if (b == 0xFF) {
+                byte stuffing = reader.getByte();
+                if (stuffing != 0x00) {
+                    throw new IOException("Marker " + JpegSegmentType.fromByte(stuffing) + " found inside DHT segment");
+                }
+            }
+            bytes[i] = b;
+        }
+        return bytes;
+    }
 }

Source/com/drew/metadata/jpeg/JpegDnlReader.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2002-2017 Drew Noakes
+ *
+ *    Licensed under the Apache License, Version 2.0 (the "License");
+ *    you may not use this file except in compliance with the License.
+ *    You may obtain a copy of the License at
+ *
+ *        http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing, software
+ *    distributed under the License is distributed on an "AS IS" BASIS,
+ *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *    See the License for the specific language governing permissions and
+ *    limitations under the License.
+ *
+ * More information about this project is available at:
+ *
+ *    https://drewnoakes.com/code/exif/
+ *    https://github.com/drewnoakes/metadata-extractor
+ */
+package com.drew.metadata.jpeg;
+
+import com.drew.imaging.jpeg.JpegSegmentMetadataReader;
+import com.drew.imaging.jpeg.JpegSegmentType;
+import com.drew.lang.SequentialByteArrayReader;
+import com.drew.lang.SequentialReader;
+import com.drew.lang.annotations.NotNull;
+import com.drew.metadata.ErrorDirectory;
+import com.drew.metadata.Metadata;
+
+import java.io.IOException;
+import java.util.Arrays;
+
+/**
+ * Decodes JPEG DNL data, adjusting the image height with information missing from the JPEG SOFx segment.
+ *
+ * @author Nadahar
+ */
+public class JpegDnlReader implements JpegSegmentMetadataReader
+{
+    @NotNull
+    public Iterable<JpegSegmentType> getSegmentTypes()
+    {
+        return Arrays.asList(JpegSegmentType.DNL);
+    }
+
+    @NotNull
+    public void readJpegSegments(@NotNull Iterable<byte[]> segments, @NotNull Metadata metadata, @NotNull JpegSegmentType segmentType)
+    {
+        for (byte[] segmentBytes : segments) {
+            extract(segmentBytes, metadata, segmentType);
+        }
+    }
+
+    public void extract(byte[] segmentBytes, Metadata metadata, JpegSegmentType segmentType)
+    {
+        JpegDirectory directory = metadata.getFirstDirectoryOfType(JpegDirectory.class);
+        if (directory == null) {
+            ErrorDirectory errorDirectory = new ErrorDirectory();
+            metadata.addDirectory(errorDirectory);
+            errorDirectory.addError("DNL segment found without SOFx - illegal JPEG format");
+        }
+
+        SequentialReader reader = new SequentialByteArrayReader(segmentBytes);
+
+        try {
+            // Only set height from DNL if it's not already defined
+            Integer i = directory.getInteger(JpegDirectory.TAG_IMAGE_HEIGHT);
+            if (i == null || i.intValue() == 0) {
+                directory.setInt(JpegDirectory.TAG_IMAGE_HEIGHT, reader.getUInt16());
+            }
+        } catch (IOException ex) {
+            directory.addError(ex.getMessage());
+        }
+    }
+}

Tests/com/drew/metadata/jpeg/HuffmanTablesDirectoryTest.java

@@ -25,6 +25,9 @@
 
 import static org.junit.Assert.*;
 
+import com.drew.metadata.jpeg.HuffmanTablesDirectory.HuffmanTable;
+import com.drew.metadata.jpeg.HuffmanTablesDirectory.HuffmanTable.HuffmanTableClass;
+
 /**
  * @author Nadahar
  */
@@ -63,4 +66,29 @@ public void testGetNumberOfTables() throws Exception
         assertEquals(9,_directory.getNumberOfTables());
         assertEquals("9 Huffman tables", _directory.getDescription(HuffmanTablesDirectory.TAG_NUMBER_OF_TABLES));
     }
+
+    @Test
+    public void testIsTypical() throws Exception
+    {
+        _directory.tables.add(new HuffmanTable(
+            HuffmanTableClass.AC,
+            0,
+            HuffmanTablesDirectory.TYPICAL_CHROMINANCE_AC_LENGTHS,
+            HuffmanTablesDirectory.TYPICAL_CHROMINANCE_AC_VALUES
+        ));
+        _directory.tables.add(new HuffmanTable(
+            HuffmanTableClass.DC,
+            0,
+            HuffmanTablesDirectory.TYPICAL_LUMINANCE_DC_LENGTHS,
+            HuffmanTablesDirectory.TYPICAL_LUMINANCE_DC_VALUES
+        ));
+
+        assertTrue(_directory.getTable(0).isTypical());
+        assertFalse(_directory.getTable(0).isOptimized());
+        assertTrue(_directory.getTable(1).isTypical());
+        assertFalse(_directory.getTable(1).isOptimized());
+
+        assertTrue(_directory.isTypical());
+        assertFalse(_directory.isOptimized());
+    }
 }