614 lines
21 KiB
C#
614 lines
21 KiB
C#
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using System;
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using System.Collections.Generic;
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using System.Globalization;
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using System.IO;
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using System.Text;
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namespace MediaBrowser.Providers.Photos
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{
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/// <summary>
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/// A class for reading Exif data from a JPEG file. The file will be open for reading for as long as the class exists.
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/// <seealso cref="http://gvsoft.homedns.org/exif/Exif-explanation.html"/>
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/// </summary>
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public class ExifReader : IDisposable
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{
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private readonly FileStream fileStream = null;
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private readonly BinaryReader reader = null;
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/// <summary>
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/// The catalogue of tag ids and their absolute offsets within the
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/// file
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/// </summary>
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private Dictionary<ushort, long> catalogue;
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/// <summary>
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/// Indicates whether to read data using big or little endian byte aligns
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/// </summary>
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private bool isLittleEndian;
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/// <summary>
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/// The position in the filestream at which the TIFF header starts
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/// </summary>
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private long tiffHeaderStart;
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public ExifReader(string fileName)
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{
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// JPEG encoding uses big endian (i.e. Motorola) byte aligns. The TIFF encoding
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// found later in the document will specify the byte aligns used for the
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// rest of the document.
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isLittleEndian = false;
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try
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{
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// Open the file in a stream
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fileStream = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
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reader = new BinaryReader(fileStream);
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// Make sure the file's a JPEG.
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if (ReadUShort() != 0xFFD8)
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throw new Exception("File is not a valid JPEG");
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// Scan to the start of the Exif content
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ReadToExifStart();
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// Create an index of all Exif tags found within the document
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CreateTagIndex();
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}
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catch (Exception)
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{
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// If instantiation fails, make sure there's no mess left behind
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Dispose();
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throw;
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}
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}
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#region TIFF methods
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/// <summary>
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/// Returns the length (in bytes) per component of the specified TIFF data type
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/// </summary>
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/// <returns></returns>
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private byte GetTIFFFieldLength(ushort tiffDataType)
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{
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switch (tiffDataType)
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{
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case 1:
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case 2:
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case 6:
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return 1;
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case 3:
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case 8:
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return 2;
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case 4:
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case 7:
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case 9:
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case 11:
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return 4;
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case 5:
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case 10:
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case 12:
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return 8;
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default:
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throw new Exception(string.Format("Unknown TIFF datatype: {0}", tiffDataType));
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}
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}
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#endregion
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#region Methods for reading data directly from the filestream
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/// <summary>
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/// Gets a 2 byte unsigned integer from the file
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/// </summary>
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/// <returns></returns>
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private ushort ReadUShort()
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{
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return ToUShort(ReadBytes(2));
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}
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/// <summary>
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/// Gets a 4 byte unsigned integer from the file
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/// </summary>
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/// <returns></returns>
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private uint ReadUint()
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{
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return ToUint(ReadBytes(4));
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}
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private string ReadString(int chars)
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{
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return Encoding.ASCII.GetString(ReadBytes(chars));
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}
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private byte[] ReadBytes(int byteCount)
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{
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return reader.ReadBytes(byteCount);
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}
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/// <summary>
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/// Reads some bytes from the specified TIFF offset
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/// </summary>
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/// <param name="tiffOffset"></param>
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/// <param name="byteCount"></param>
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/// <returns></returns>
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private byte[] ReadBytes(ushort tiffOffset, int byteCount)
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{
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// Keep the current file offset
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long originalOffset = fileStream.Position;
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// Move to the TIFF offset and retrieve the data
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fileStream.Seek(tiffOffset + tiffHeaderStart, SeekOrigin.Begin);
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byte[] data = reader.ReadBytes(byteCount);
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// Restore the file offset
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fileStream.Position = originalOffset;
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return data;
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}
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#endregion
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#region Data conversion methods for interpreting datatypes from a byte array
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/// <summary>
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/// Converts 2 bytes to a ushort using the current byte aligns
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/// </summary>
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/// <returns></returns>
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private ushort ToUShort(byte[] data)
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{
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if (isLittleEndian != BitConverter.IsLittleEndian)
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Array.Reverse(data);
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return BitConverter.ToUInt16(data, 0);
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}
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/// <summary>
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/// Converts 8 bytes to an unsigned rational using the current byte aligns.
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/// </summary>
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/// <param name="data"></param>
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/// <returns></returns>
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/// <seealso cref="ToRational"/>
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private double ToURational(byte[] data)
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{
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var numeratorData = new byte[4];
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var denominatorData = new byte[4];
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Array.Copy(data, numeratorData, 4);
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Array.Copy(data, 4, denominatorData, 0, 4);
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uint numerator = ToUint(numeratorData);
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uint denominator = ToUint(denominatorData);
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return numerator / (double)denominator;
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}
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/// <summary>
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/// Converts 8 bytes to a signed rational using the current byte aligns.
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/// </summary>
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/// <remarks>
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/// A TIFF rational contains 2 4-byte integers, the first of which is
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/// the numerator, and the second of which is the denominator.
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/// </remarks>
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/// <param name="data"></param>
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/// <returns></returns>
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private double ToRational(byte[] data)
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{
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var numeratorData = new byte[4];
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var denominatorData = new byte[4];
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Array.Copy(data, numeratorData, 4);
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Array.Copy(data, 4, denominatorData, 0, 4);
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int numerator = ToInt(numeratorData);
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int denominator = ToInt(denominatorData);
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return numerator / (double)denominator;
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}
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/// <summary>
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/// Converts 4 bytes to a uint using the current byte aligns
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/// </summary>
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/// <returns></returns>
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private uint ToUint(byte[] data)
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{
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if (isLittleEndian != BitConverter.IsLittleEndian)
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Array.Reverse(data);
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return BitConverter.ToUInt32(data, 0);
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}
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/// <summary>
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/// Converts 4 bytes to an int using the current byte aligns
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/// </summary>
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/// <returns></returns>
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private int ToInt(byte[] data)
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{
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if (isLittleEndian != BitConverter.IsLittleEndian)
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Array.Reverse(data);
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return BitConverter.ToInt32(data, 0);
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}
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private double ToDouble(byte[] data)
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{
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if (isLittleEndian != BitConverter.IsLittleEndian)
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Array.Reverse(data);
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return BitConverter.ToDouble(data, 0);
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}
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private float ToSingle(byte[] data)
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{
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if (isLittleEndian != BitConverter.IsLittleEndian)
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Array.Reverse(data);
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return BitConverter.ToSingle(data, 0);
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}
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private short ToShort(byte[] data)
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{
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if (isLittleEndian != BitConverter.IsLittleEndian)
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Array.Reverse(data);
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return BitConverter.ToInt16(data, 0);
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}
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private sbyte ToSByte(byte[] data)
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{
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// An sbyte should just be a byte with an offset range.
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return (sbyte)(data[0] - byte.MaxValue);
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}
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/// <summary>
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/// Retrieves an array from a byte array using the supplied converter
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/// to read each individual element from the supplied byte array
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/// </summary>
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/// <param name="data"></param>
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/// <param name="elementLengthBytes"></param>
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/// <param name="converter"></param>
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/// <returns></returns>
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private Array GetArray<T>(byte[] data, int elementLengthBytes, ConverterMethod<T> converter)
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{
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Array convertedData = Array.CreateInstance(typeof(T), data.Length / elementLengthBytes);
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var buffer = new byte[elementLengthBytes];
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// Read each element from the array
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for (int elementCount = 0; elementCount < data.Length / elementLengthBytes; elementCount++)
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{
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// Place the data for the current element into the buffer
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Array.Copy(data, elementCount * elementLengthBytes, buffer, 0, elementLengthBytes);
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// Process the data and place it into the output array
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convertedData.SetValue(converter(buffer), elementCount);
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}
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return convertedData;
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}
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/// <summary>
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/// A delegate used to invoke any of the data conversion methods
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/// </summary>
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/// <param name="data"></param>
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/// <returns></returns>
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private delegate T ConverterMethod<out T>(byte[] data);
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#endregion
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#region Stream seek methods - used to get to locations within the JPEG
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/// <summary>
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/// Scans to the Exif block
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/// </summary>
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private void ReadToExifStart()
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{
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// The file has a number of blocks (Exif/JFIF), each of which
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// has a tag number followed by a length. We scan the document until the required tag (0xFFE1)
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// is found. All tags start with FF, so a non FF tag indicates an error.
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// Get the next tag.
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byte markerStart;
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byte markerNumber = 0;
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while (((markerStart = reader.ReadByte()) == 0xFF) && (markerNumber = reader.ReadByte()) != 0xE1)
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{
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// Get the length of the data.
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ushort dataLength = ReadUShort();
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// Jump to the end of the data (note that the size field includes its own size)!
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reader.BaseStream.Seek(dataLength - 2, SeekOrigin.Current);
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}
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// It's only success if we found the 0xFFE1 marker
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if (markerStart != 0xFF || markerNumber != 0xE1)
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throw new Exception("Could not find Exif data block");
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}
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/// <summary>
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/// Reads through the Exif data and builds an index of all Exif tags in the document
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/// </summary>
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/// <returns></returns>
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private void CreateTagIndex()
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{
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// The next 4 bytes are the size of the Exif data.
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ReadUShort();
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// Next is the Exif data itself. It starts with the ASCII "Exif" followed by 2 zero bytes.
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if (ReadString(4) != "Exif")
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throw new Exception("Exif data not found");
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// 2 zero bytes
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if (ReadUShort() != 0)
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throw new Exception("Malformed Exif data");
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// We're now into the TIFF format
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tiffHeaderStart = reader.BaseStream.Position;
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// What byte align will be used for the TIFF part of the document? II for Intel, MM for Motorola
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isLittleEndian = ReadString(2) == "II";
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// Next 2 bytes are always the same.
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if (ReadUShort() != 0x002A)
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throw new Exception("Error in TIFF data");
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// Get the offset to the IFD (image file directory)
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uint ifdOffset = ReadUint();
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// Note that this offset is from the first byte of the TIFF header. Jump to the IFD.
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fileStream.Position = ifdOffset + tiffHeaderStart;
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// Catalogue this first IFD (there will be another IFD)
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CatalogueIFD();
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// There's more data stored in the subifd, the offset to which is found in tag 0x8769.
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// As with all TIFF offsets, it will be relative to the first byte of the TIFF header.
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uint offset;
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if (!GetTagValue(0x8769, out offset))
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throw new Exception("Unable to locate Exif data");
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// Jump to the exif SubIFD
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fileStream.Position = offset + tiffHeaderStart;
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// Add the subIFD to the catalogue too
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CatalogueIFD();
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// Go to the GPS IFD and catalogue that too. It's an optional
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// section.
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if (GetTagValue(0x8825, out offset))
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{
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// Jump to the GPS SubIFD
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fileStream.Position = offset + tiffHeaderStart;
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// Add the subIFD to the catalogue too
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CatalogueIFD();
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
#endregion
|
|||
|
|
|
|||
|
|
#region Exif data catalog and retrieval methods
|
|||
|
|
|
|||
|
|
public bool GetTagValue<T>(ExifTags tag, out T result)
|
|||
|
|
{
|
|||
|
|
return GetTagValue((ushort)tag, out result);
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
/// <summary>
|
|||
|
|
/// Retrieves an Exif value with the requested tag ID
|
|||
|
|
/// </summary>
|
|||
|
|
/// <param name="tagID"></param>
|
|||
|
|
/// <param name="result"></param>
|
|||
|
|
/// <returns></returns>
|
|||
|
|
public bool GetTagValue<T>(ushort tagID, out T result)
|
|||
|
|
{
|
|||
|
|
ushort tiffDataType;
|
|||
|
|
uint numberOfComponents;
|
|||
|
|
byte[] tagData = GetTagBytes(tagID, out tiffDataType, out numberOfComponents);
|
|||
|
|
|
|||
|
|
if (tagData == null)
|
|||
|
|
{
|
|||
|
|
result = default(T);
|
|||
|
|
return false;
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
byte fieldLength = GetTIFFFieldLength(tiffDataType);
|
|||
|
|
|
|||
|
|
// Convert the data to the appropriate datatype. Note the weird boxing via object.
|
|||
|
|
// The compiler doesn't like it otherwise.
|
|||
|
|
switch (tiffDataType)
|
|||
|
|
{
|
|||
|
|
case 1:
|
|||
|
|
// unsigned byte
|
|||
|
|
if (numberOfComponents == 1)
|
|||
|
|
result = (T)(object)tagData[0];
|
|||
|
|
else
|
|||
|
|
result = (T)(object)tagData;
|
|||
|
|
return true;
|
|||
|
|
case 2:
|
|||
|
|
// ascii string
|
|||
|
|
string str = Encoding.ASCII.GetString(tagData);
|
|||
|
|
|
|||
|
|
// There may be a null character within the string
|
|||
|
|
int nullCharIndex = str.IndexOf('\0');
|
|||
|
|
if (nullCharIndex != -1)
|
|||
|
|
str = str.Substring(0, nullCharIndex);
|
|||
|
|
|
|||
|
|
// Special processing for dates.
|
|||
|
|
if (typeof(T) == typeof(DateTime))
|
|||
|
|
{
|
|||
|
|
result =
|
|||
|
|
(T)(object)DateTime.ParseExact(str, "yyyy:MM:dd HH:mm:ss", CultureInfo.InvariantCulture);
|
|||
|
|
return true;
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
result = (T)(object)str;
|
|||
|
|
return true;
|
|||
|
|
case 3:
|
|||
|
|
// unsigned short
|
|||
|
|
if (numberOfComponents == 1)
|
|||
|
|
result = (T)(object)ToUShort(tagData);
|
|||
|
|
else
|
|||
|
|
result = (T)(object)GetArray(tagData, fieldLength, ToUShort);
|
|||
|
|
return true;
|
|||
|
|
case 4:
|
|||
|
|
// unsigned long
|
|||
|
|
if (numberOfComponents == 1)
|
|||
|
|
result = (T)(object)ToUint(tagData);
|
|||
|
|
else
|
|||
|
|
result = (T)(object)GetArray(tagData, fieldLength, ToUint);
|
|||
|
|
return true;
|
|||
|
|
case 5:
|
|||
|
|
// unsigned rational
|
|||
|
|
if (numberOfComponents == 1)
|
|||
|
|
result = (T)(object)ToURational(tagData);
|
|||
|
|
else
|
|||
|
|
result = (T)(object)GetArray(tagData, fieldLength, ToURational);
|
|||
|
|
return true;
|
|||
|
|
case 6:
|
|||
|
|
// signed byte
|
|||
|
|
if (numberOfComponents == 1)
|
|||
|
|
result = (T)(object)ToSByte(tagData);
|
|||
|
|
else
|
|||
|
|
result = (T)(object)GetArray(tagData, fieldLength, ToSByte);
|
|||
|
|
return true;
|
|||
|
|
case 7:
|
|||
|
|
// undefined. Treat it as an unsigned integer.
|
|||
|
|
if (numberOfComponents == 1)
|
|||
|
|
result = (T)(object)ToUint(tagData);
|
|||
|
|
else
|
|||
|
|
result = (T)(object)GetArray(tagData, fieldLength, ToUint);
|
|||
|
|
return true;
|
|||
|
|
case 8:
|
|||
|
|
// Signed short
|
|||
|
|
if (numberOfComponents == 1)
|
|||
|
|
result = (T)(object)ToShort(tagData);
|
|||
|
|
else
|
|||
|
|
result = (T)(object)GetArray(tagData, fieldLength, ToShort);
|
|||
|
|
return true;
|
|||
|
|
case 9:
|
|||
|
|
// Signed long
|
|||
|
|
if (numberOfComponents == 1)
|
|||
|
|
result = (T)(object)ToInt(tagData);
|
|||
|
|
else
|
|||
|
|
result = (T)(object)GetArray(tagData, fieldLength, ToInt);
|
|||
|
|
return true;
|
|||
|
|
case 10:
|
|||
|
|
// signed rational
|
|||
|
|
if (numberOfComponents == 1)
|
|||
|
|
result = (T)(object)ToRational(tagData);
|
|||
|
|
else
|
|||
|
|
result = (T)(object)GetArray(tagData, fieldLength, ToRational);
|
|||
|
|
return true;
|
|||
|
|
case 11:
|
|||
|
|
// single float
|
|||
|
|
if (numberOfComponents == 1)
|
|||
|
|
result = (T)(object)ToSingle(tagData);
|
|||
|
|
else
|
|||
|
|
result = (T)(object)GetArray(tagData, fieldLength, ToSingle);
|
|||
|
|
return true;
|
|||
|
|
case 12:
|
|||
|
|
// double float
|
|||
|
|
if (numberOfComponents == 1)
|
|||
|
|
result = (T)(object)ToDouble(tagData);
|
|||
|
|
else
|
|||
|
|
result = (T)(object)GetArray(tagData, fieldLength, ToDouble);
|
|||
|
|
return true;
|
|||
|
|
default:
|
|||
|
|
throw new Exception(string.Format("Unknown TIFF datatype: {0}", tiffDataType));
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
/// <summary>
|
|||
|
|
/// Gets the data in the specified tag ID, starting from before the IFD block.
|
|||
|
|
/// </summary>
|
|||
|
|
/// <param name="tiffDataType"></param>
|
|||
|
|
/// <param name="numberOfComponents">The number of items which make up the data item - i.e. for a string, this will be the
|
|||
|
|
/// number of characters in the string</param>
|
|||
|
|
/// <param name="tagID"></param>
|
|||
|
|
private byte[] GetTagBytes(ushort tagID, out ushort tiffDataType, out uint numberOfComponents)
|
|||
|
|
{
|
|||
|
|
// Get the tag's offset from the catalogue and do some basic error checks
|
|||
|
|
if (fileStream == null || reader == null || catalogue == null || !catalogue.ContainsKey(tagID))
|
|||
|
|
{
|
|||
|
|
tiffDataType = 0;
|
|||
|
|
numberOfComponents = 0;
|
|||
|
|
return null;
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
long tagOffset = catalogue[tagID];
|
|||
|
|
|
|||
|
|
// Jump to the TIFF offset
|
|||
|
|
fileStream.Position = tagOffset;
|
|||
|
|
|
|||
|
|
// Read the tag number from the file
|
|||
|
|
ushort currentTagID = ReadUShort();
|
|||
|
|
|
|||
|
|
if (currentTagID != tagID)
|
|||
|
|
throw new Exception("Tag number not at expected offset");
|
|||
|
|
|
|||
|
|
// Read the offset to the Exif IFD
|
|||
|
|
tiffDataType = ReadUShort();
|
|||
|
|
numberOfComponents = ReadUint();
|
|||
|
|
byte[] tagData = ReadBytes(4);
|
|||
|
|
|
|||
|
|
// If the total space taken up by the field is longer than the
|
|||
|
|
// 2 bytes afforded by the tagData, tagData will contain an offset
|
|||
|
|
// to the actual data.
|
|||
|
|
var dataSize = (int)(numberOfComponents * GetTIFFFieldLength(tiffDataType));
|
|||
|
|
|
|||
|
|
if (dataSize > 4)
|
|||
|
|
{
|
|||
|
|
ushort offsetAddress = ToUShort(tagData);
|
|||
|
|
return ReadBytes(offsetAddress, dataSize);
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
// The value is stored in the tagData starting from the left
|
|||
|
|
Array.Resize(ref tagData, dataSize);
|
|||
|
|
|
|||
|
|
return tagData;
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
/// <summary>
|
|||
|
|
/// Records all Exif tags and their offsets within
|
|||
|
|
/// the file from the current IFD
|
|||
|
|
/// </summary>
|
|||
|
|
private void CatalogueIFD()
|
|||
|
|
{
|
|||
|
|
if (catalogue == null)
|
|||
|
|
catalogue = new Dictionary<ushort, long>();
|
|||
|
|
|
|||
|
|
// Assume we're just before the IFD.
|
|||
|
|
|
|||
|
|
// First 2 bytes is the number of entries in this IFD
|
|||
|
|
ushort entryCount = ReadUShort();
|
|||
|
|
|
|||
|
|
for (ushort currentEntry = 0; currentEntry < entryCount; currentEntry++)
|
|||
|
|
{
|
|||
|
|
ushort currentTagNumber = ReadUShort();
|
|||
|
|
|
|||
|
|
// Record this in the catalogue
|
|||
|
|
catalogue[currentTagNumber] = fileStream.Position - 2;
|
|||
|
|
|
|||
|
|
// Go to the end of this item (10 bytes, as each entry is 12 bytes long)
|
|||
|
|
reader.BaseStream.Seek(10, SeekOrigin.Current);
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
#endregion
|
|||
|
|
|
|||
|
|
#region IDisposable Members
|
|||
|
|
|
|||
|
|
public void Dispose()
|
|||
|
|
{
|
|||
|
|
// Make sure the file handle is released
|
|||
|
|
if (reader != null)
|
|||
|
|
reader.Close();
|
|||
|
|
if (fileStream != null)
|
|||
|
|
fileStream.Close();
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
#endregion
|
|||
|
|
}
|
|||
|
|
}
|