public PNGText(ExifTag tag, string keyword, string value, bool compressed)
     : base(tag)
 {
     Keyword = keyword;
     mValue = value;
     Compressed = compressed;
 }

 private void AddTagToList(ExifTag tag)
 {
     ListViewItem item = listExif.Items.Add(tag.Id.ToString());
     item.SubItems.Add(tag.FieldName);
     item.SubItems.Add(tag.Description);
     item.SubItems.Add(tag.Value);
 }

 /// <summary>
 /// Returns the string representation for the given exif tag.
 /// </summary>
 public static string GetTagName(ExifTag tag)
 {
     string name = Enum.GetName(typeof(ExifTag), tag);
     if (name == null)
         return "Unknown";
     else
         return name;
 }

 /// <summary>
 /// Returns the string representation for the given exif tag including 
 /// IFD section and tag id.
 /// </summary>
 public static string GetTagLongName(ExifTag tag)
 {
     string ifdname = Enum.GetName(typeof(IFD), GetTagIFD(tag));
     string name = Enum.GetName(typeof(ExifTag), tag);
     if (name == null)
         name = "Unknown";
     string tagidname = GetTagID(tag).ToString();
     return ifdname + ": " + name + " (" + tagidname + ")";
 }

 public PNGInternationalText(ExifTag tag, string keyword, string value, bool compressed, string language, string translatedKeyword)
     : base(tag)
 {
     Keyword = keyword;
     mValue = value;
     Compressed = compressed;
     Language = language;
     TranslatedKeyword = translatedKeyword;
 }

	bool MakeExifNode (TreeIter parent, TreeIter iter, ExifData ed, ExifTag tag)
	{
		string val = ed.Lookup (tag);
		if (val == null || val == "")
			return false;

		MakeNode (parent, out iter, ExifUtil.GetTagTitle (tag) + ":", ed.Lookup (tag));
		return true;
	}

 /// <summary>
 /// Gets or sets the Exif property with the given key.
 /// </summary>
 /// <param name="key">The Exif tag associated with the Exif property.</param>
 /// <returns></returns>
 public ExifProperty this[ExifTag key]
 {
     get
     {
         return Properties[key];
     }
     set
     {
         Properties[key] = value;
     }
 }

    public static string GetDescription(ExifTag tag, object value)
    {
      ExifTagDescriptionAttribute[] attributes = TypeHelper.GetCustomAttributes<ExifTagDescriptionAttribute>(tag);

      if (attributes == null || attributes.Length == 0)
        return null;

      foreach (ExifTagDescriptionAttribute attribute in attributes)
      {
        if (Equals(attribute._value, value))
          return attribute._description;
      }

      return null;
    }

 public ExifTag GetExifData(string filename)
 {
   Metadata fileMetadata = GetExifMetadata(filename);
   ExifTag newTags = new ExifTag();
   newTags.CameraModel = fileMetadata.CameraModel.DisplayValue;
   newTags.EquipmentMake = fileMetadata.EquipmentMake.DisplayValue;
   newTags.Date = fileMetadata.DatePictureTaken.DisplayValue;
   newTags.ExposureCompensation = fileMetadata.ExposureCompensation.DisplayValue;
   newTags.ExposureTime = fileMetadata.ExposureTime.DisplayValue;
   newTags.Flash = fileMetadata.Flash.DisplayValue;
   newTags.Fstop = fileMetadata.Fstop.DisplayValue;
   newTags.ImgDimensions = fileMetadata.ImageDimensions.DisplayValue;
   newTags.MeteringMod = fileMetadata.MeteringMode.DisplayValue;
   newTags.Resolutions = fileMetadata.Resolution.DisplayValue;
   newTags.ShutterSpeed = fileMetadata.ShutterSpeed.DisplayValue;
   newTags.ViewComment = fileMetadata.ViewerComments.DisplayValue;
   return newTags;
 }

 public ExifSIntArray(ExifTag tag, int[] value)
     : base(tag)
 {
     mValue = value;
 }

 public ExifSRational(ExifTag tag, int numerator, int denominator)
     : base(tag)
 {
     mValue = new MathEx.Fraction32(numerator, denominator);
 }

 public ExifUndefined(ExifTag tag, byte[] value)
     : base(tag)
 {
     mValue = value;
 }

 public ExifSInt(ExifTag tag, int value)
     : base(tag)
 {
     mValue = value;
 }

	internal static extern IntPtr exif_content_get_entry (_ExifContent *ptr, ExifTag tag);

 public ExifProperty(ExifTag tag)
 {
     mTag = tag;
     mIFD = ExifTagFactory.GetTagIFD(tag);
 }

 public ExifUShort(ExifTag tag, ushort value)
     : base(tag)
 {
     mValue = value;
 }

 public ExifByteArray(ExifTag tag, byte[] value)
     : base(tag)
 {
     mValue = value;
 }

		public Boolean RemoveValue(ExifTag tag)
		{
			object result;
			try
			{
				result = _Instance.CallMethod("RemoveValue", new Type[] {Types.ExifTag}, tag);
			}
			catch (Exception ex)
			{
				throw ExceptionHelper.Create(ex);
			}
			return (Boolean)result;
		}

	public static string GetTagTitle (ExifTag tag)
	{
		return "";
	}

	unsafe internal _ExifEntry * Search (ExifTag tag)
	{
		return null;
	}