Wie immer ist es am besten, eine gut getestete Bibliothek zu finden. Sie sagten jedoch, dass dies schwierig ist. Hier ist ein zwielichtiger, weitgehend ungetesteter Code, der für eine ganze Reihe von Fällen funktionieren sollte:
using System;
using System.Collections.Generic;
using System.Drawing;
using System.IO;
using System.Linq;
namespace ImageDimensions
{
public static class ImageHelper
{
const string errorMessage = "Could not recognize image format.";
private static Dictionary<byte[], Func<BinaryReader, Size>> imageFormatDecoders = new Dictionary<byte[], Func<BinaryReader, Size>>()
{
{ new byte[]{ 0x42, 0x4D }, DecodeBitmap},
{ new byte[]{ 0x47, 0x49, 0x46, 0x38, 0x37, 0x61 }, DecodeGif },
{ new byte[]{ 0x47, 0x49, 0x46, 0x38, 0x39, 0x61 }, DecodeGif },
{ new byte[]{ 0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A }, DecodePng },
{ new byte[]{ 0xff, 0xd8 }, DecodeJfif },
};
/// <summary>
/// Gets the dimensions of an image.
/// </summary>
/// <param name="path">The path of the image to get the dimensions of.</param>
/// <returns>The dimensions of the specified image.</returns>
/// <exception cref="ArgumentException">The image was of an unrecognized format.</exception>
public static Size GetDimensions(string path)
{
using (BinaryReader binaryReader = new BinaryReader(File.OpenRead(path)))
{
try
{
return GetDimensions(binaryReader);
}
catch (ArgumentException e)
{
if (e.Message.StartsWith(errorMessage))
{
throw new ArgumentException(errorMessage, "path", e);
}
else
{
throw e;
}
}
}
}
/// <summary>
/// Gets the dimensions of an image.
/// </summary>
/// <param name="path">The path of the image to get the dimensions of.</param>
/// <returns>The dimensions of the specified image.</returns>
/// <exception cref="ArgumentException">The image was of an unrecognized format.</exception>
public static Size GetDimensions(BinaryReader binaryReader)
{
int maxMagicBytesLength = imageFormatDecoders.Keys.OrderByDescending(x => x.Length).First().Length;
byte[] magicBytes = new byte[maxMagicBytesLength];
for (int i = 0; i < maxMagicBytesLength; i += 1)
{
magicBytes[i] = binaryReader.ReadByte();
foreach(var kvPair in imageFormatDecoders)
{
if (magicBytes.StartsWith(kvPair.Key))
{
return kvPair.Value(binaryReader);
}
}
}
throw new ArgumentException(errorMessage, "binaryReader");
}
private static bool StartsWith(this byte[] thisBytes, byte[] thatBytes)
{
for(int i = 0; i < thatBytes.Length; i+= 1)
{
if (thisBytes[i] != thatBytes[i])
{
return false;
}
}
return true;
}
private static short ReadLittleEndianInt16(this BinaryReader binaryReader)
{
byte[] bytes = new byte[sizeof(short)];
for (int i = 0; i < sizeof(short); i += 1)
{
bytes[sizeof(short) - 1 - i] = binaryReader.ReadByte();
}
return BitConverter.ToInt16(bytes, 0);
}
private static int ReadLittleEndianInt32(this BinaryReader binaryReader)
{
byte[] bytes = new byte[sizeof(int)];
for (int i = 0; i < sizeof(int); i += 1)
{
bytes[sizeof(int) - 1 - i] = binaryReader.ReadByte();
}
return BitConverter.ToInt32(bytes, 0);
}
private static Size DecodeBitmap(BinaryReader binaryReader)
{
binaryReader.ReadBytes(16);
int width = binaryReader.ReadInt32();
int height = binaryReader.ReadInt32();
return new Size(width, height);
}
private static Size DecodeGif(BinaryReader binaryReader)
{
int width = binaryReader.ReadInt16();
int height = binaryReader.ReadInt16();
return new Size(width, height);
}
private static Size DecodePng(BinaryReader binaryReader)
{
binaryReader.ReadBytes(8);
int width = binaryReader.ReadLittleEndianInt32();
int height = binaryReader.ReadLittleEndianInt32();
return new Size(width, height);
}
private static Size DecodeJfif(BinaryReader binaryReader)
{
while (binaryReader.ReadByte() == 0xff)
{
byte marker = binaryReader.ReadByte();
short chunkLength = binaryReader.ReadLittleEndianInt16();
if (marker == 0xc0)
{
binaryReader.ReadByte();
int height = binaryReader.ReadLittleEndianInt16();
int width = binaryReader.ReadLittleEndianInt16();
return new Size(width, height);
}
binaryReader.ReadBytes(chunkLength - 2);
}
throw new ArgumentException(errorMessage);
}
}
}
Hoffentlich ist der Code ziemlich offensichtlich. Um ein neues Dateiformat hinzuzufügen, fügen Sie es hinzu, imageFormatDecoderswobei der Schlüssel ein Array der "magischen Bits" ist, die am Anfang jeder Datei des angegebenen Formats erscheinen, und der Wert eine Funktion ist, die die Größe aus dem Stream extrahiert. Die meisten Formate sind einfach genug, der einzige echte Stinker ist JPEG.