Merge pull request #329 from RupertAvery/fix-328

Fixes Issue #328

Author: drewnoakes

MetadataExtractor/Formats/Png/PngMetadataReader.cs

@@ -90,6 +90,7 @@ public static DirectoryList ReadMetadata(Stream stream)
         /// For more guidance: http://www.w3.org/TR/PNG-Decoders.html#D.Text-chunk-processing
         /// </summary>
         private static readonly Encoding _latin1Encoding = Encoding.GetEncoding("ISO-8859-1");
+        private static readonly Encoding _utf8Encoding = Encoding.UTF8;
 
         /// <exception cref="PngProcessingException"/>
         /// <exception cref="IOException"/>
@@ -248,15 +249,18 @@ private static IEnumerable<Directory> ProcessChunk(PngChunk chunk)
             else if (chunkType == PngChunkType.iTXt)
             {
                 var reader = new SequentialByteArrayReader(bytes);
-                var keyword = reader.GetNullTerminatedStringValue(maxLengthBytes: 79).ToString(_latin1Encoding);
+                var keywordStringValue = reader.GetNullTerminatedStringValue(maxLengthBytes: 79);
+                var keyword = keywordStringValue.ToString(_utf8Encoding);
                 var compressionFlag = reader.GetSByte();
                 var compressionMethod = reader.GetSByte();
 
                 // TODO we currently ignore languageTagBytes and translatedKeywordBytes
                 var languageTagBytes = reader.GetNullTerminatedBytes(bytes.Length);
                 var translatedKeywordBytes = reader.GetNullTerminatedBytes(bytes.Length);
 
-                var bytesLeft = bytes.Length - keyword.Length - 1 - 1 - 1 - languageTagBytes.Length - 1 - translatedKeywordBytes.Length - 1;
+                // bytes left for compressed text is:
+                // total bytes length - (Keyword length + null byte + comp flag byte + comp method byte + lang length + null byte + translated length + null byte)
+                var bytesLeft = bytes.Length - keywordStringValue.Bytes.Length - 1 - 1 - 1 - languageTagBytes.Length - 1 - translatedKeywordBytes.Length - 1;
                 byte[]? textBytes = null;
                 if (compressionFlag == 0)
                 {
@@ -432,7 +436,14 @@ IEnumerable<Directory> ProcessTextChunk(string keyword, byte[] textBytes)
 
                 static PngDirectory ReadTextDirectory(string keyword, byte[] textBytes, PngChunkType pngChunkType)
                 {
-                    var textPairs = new[] { new KeyValuePair(keyword, new StringValue(textBytes, _latin1Encoding)) };
+                    var encoding = _latin1Encoding;
+
+                    if (pngChunkType == PngChunkType.iTXt)
+                    {
+                        encoding = _utf8Encoding;
+                    }
+
+                    var textPairs = new[] { new KeyValuePair(keyword, new StringValue(textBytes, encoding)) };
                     var directory = new PngDirectory(pngChunkType);
                     directory.Set(PngDirectory.TagTextualData, textPairs);
                     return directory;