有没有一种便宜的方法来获取图像（jpg、png等）的尺寸？最好只使用标准类库（因为托管限制）。我知道读取图像头并自己解析应该相对容易，但似乎应该已经有这样的东西了。另外，我已经验证了下面的代码会读取整个图像（这不是我想要的）：
using System;
using System.Drawing;
namespace Test
{
class Program
{
static void Main(string[] args)
{
Image img = new Bitmap("test.png");
System.Console.WriteLine(img.Width + " x " + img.Height);
}
}
}
像往常一样，您最好找到一个经过充分测试的库。然而，您说这很困难，因此以下是一些不太可靠且未经充分测试的代码，它应该适用于相当数量的情况：
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);
}
}
}
希望代码相当明显。 要添加新的文件格式，您将其添加到imageFormatDecoders 中，其键是给定格式的每个文件开头出现的“magic bits”的数组，值是从流中提取大小的函数。 大多数格式都足够简单，唯一真正棘手的是jpeg。
throw e; 而是应该直接写 throw;。您在第二个 GetDimensions 的 XML 文档注释中也显示了 path 而非 binaryReader。 - EregrithSystem.Drawing现在已经不是标准库了；它依赖于GDI+，并且有很多C#平台上不可用。 - Nyergudsusing (FileStream file = new FileStream(this.ImageFileName, FileMode.Open, FileAccess.Read))
{
using (Image tif = Image.FromStream(stream: file,
useEmbeddedColorManagement: false,
validateImageData: false))
{
float width = tif.PhysicalDimension.Width;
float height = tif.PhysicalDimension.Height;
float hresolution = tif.HorizontalResolution;
float vresolution = tif.VerticalResolution;
}
}
validateImageData设置为false可以防止GDI+对图像数据进行昂贵的分析，从而严重减少加载时间。此问题更详细地介绍了这个主题。
new Bitmap()的方式快得多。 - AeonOfTime你尝试过使用WPF图像处理类吗？例如System.Windows.Media.Imaging.BitmapDecoder等。
我相信有些工作已经投入到确保这些编解码器只读取文件的子集以确定标头信息。值得检查一下。
几个月前，我在寻找类似的东西。 我想读取GIF图像的类型、版本、高度和宽度，但在网上找不到任何有用的信息。
幸运的是，在GIF的情况下，所有需要的信息都在前10个字节中：
Type: Bytes 0-2
Version: Bytes 3-5
Height: Bytes 6-7
Width: Bytes 8-9
PNG 格式略微复杂一些（宽度和高度各占用 4 字节）：
Width: Bytes 16-19
Height: Bytes 20-23
如上所述，wotsit是一个涉及图像和数据格式详细规范的好网站，尽管在pnglib上的PNG规范更为详细。然而，我认为维基百科关于PNG和GIF格式的条目是开始了解的最佳位置。
这是我检查GIF的原始代码，我也整合了一些PNG：
using System;
using System.IO;
using System.Text;
public class ImageSizeTest
{
public static void Main()
{
byte[] bytes = new byte[10];
string gifFile = @"D:\Personal\Images&Pics\iProduct.gif";
using (FileStream fs = File.OpenRead(gifFile))
{
fs.Read(bytes, 0, 10); // type (3 bytes), version (3 bytes), width (2 bytes), height (2 bytes)
}
displayGifInfo(bytes);
string pngFile = @"D:\Personal\Images&Pics\WaveletsGamma.png";
using (FileStream fs = File.OpenRead(pngFile))
{
fs.Seek(16, SeekOrigin.Begin); // jump to the 16th byte where width and height information is stored
fs.Read(bytes, 0, 8); // width (4 bytes), height (4 bytes)
}
displayPngInfo(bytes);
}
public static void displayGifInfo(byte[] bytes)
{
string type = Encoding.ASCII.GetString(bytes, 0, 3);
string version = Encoding.ASCII.GetString(bytes, 3, 3);
int width = bytes[6] | bytes[7] << 8; // byte 6 and 7 contain the width but in network byte order so byte 7 has to be left-shifted 8 places and bit-masked to byte 6
int height = bytes[8] | bytes[9] << 8; // same for height
Console.WriteLine("GIF\nType: {0}\nVersion: {1}\nWidth: {2}\nHeight: {3}\n", type, version, width, height);
}
public static void displayPngInfo(byte[] bytes)
{
int width = 0, height = 0;
for (int i = 0; i <= 3; i++)
{
width = bytes[i] | width << 8;
height = bytes[i + 4] | height << 8;
}
Console.WriteLine("PNG\nWidth: {0}\nHeight: {1}\n", width, height);
}
}
using System;
using System.IO;
namespace Test
{
class Program
{
static bool GetJpegDimension(
string fileName,
out int width,
out int height)
{
width = height = 0;
bool found = false;
bool eof = false;
FileStream stream = new FileStream(
fileName,
FileMode.Open,
FileAccess.Read);
BinaryReader reader = new BinaryReader(stream);
while (!found || eof)
{
// read 0xFF and the type
reader.ReadByte();
byte type = reader.ReadByte();
// get length
int len = 0;
switch (type)
{
// start and end of the image
case 0xD8:
case 0xD9:
len = 0;
break;
// restart interval
case 0xDD:
len = 2;
break;
// the next two bytes is the length
default:
int lenHi = reader.ReadByte();
int lenLo = reader.ReadByte();
len = (lenHi << 8 | lenLo) - 2;
break;
}
// EOF?
if (type == 0xD9)
eof = true;
// process the data
if (len > 0)
{
// read the data
byte[] data = reader.ReadBytes(len);
// this is what we are looking for
if (type == 0xC0)
{
width = data[1] << 8 | data[2];
height = data[3] << 8 | data[4];
found = true;
}
}
}
reader.Close();
stream.Close();
return found;
}
static void Main(string[] args)
{
foreach (string file in Directory.GetFiles(args[0]))
{
int w, h;
GetJpegDimension(file, out w, out h);
System.Console.WriteLine(file + ": " + w + " x " + h);
}
}
}
}
已更新ICR的答案，支持渐进式JPEG和WebP :)
internal static class ImageHelper
{
const string errorMessage = "Could not recognise 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 },
{ new byte[] { 0x52, 0x49, 0x46, 0x46 }, DecodeWebP },
};
/// <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 unrecognised 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(StartsWith(magicBytes, kvPair.Key))
{
return kvPair.Value(binaryReader);
}
}
}
throw new ArgumentException(errorMessage, "binaryReader");
}
private static bool StartsWith(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(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(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 = ReadLittleEndianInt32(binaryReader);
int height = ReadLittleEndianInt32(binaryReader);
return new Size(width, height);
}
private static Size DecodeJfif(BinaryReader binaryReader)
{
while(binaryReader.ReadByte() == 0xff)
{
byte marker = binaryReader.ReadByte();
short chunkLength = ReadLittleEndianInt16(binaryReader);
if(marker == 0xc0 || marker == 0xc2) // c2: progressive
{
binaryReader.ReadByte();
int height = ReadLittleEndianInt16(binaryReader);
int width = ReadLittleEndianInt16(binaryReader);
return new Size(width, height);
}
if(chunkLength < 0)
{
ushort uchunkLength = (ushort)chunkLength;
binaryReader.ReadBytes(uchunkLength - 2);
}
else
{
binaryReader.ReadBytes(chunkLength - 2);
}
}
throw new ArgumentException(errorMessage);
}
private static Size DecodeWebP(BinaryReader binaryReader)
{
binaryReader.ReadUInt32(); // Size
binaryReader.ReadBytes(15); // WEBP, VP8 + more
binaryReader.ReadBytes(3); // SYNC
var width = binaryReader.ReadUInt16() & 0b00_11111111111111; // 14 bits width
var height = binaryReader.ReadUInt16() & 0b00_11111111111111; // 14 bits height
return new Size(width, height);
}
}
BinaryReader始终读取小端字节序，因此现有的辅助函数是无用的。 - NyergudsBinaryReader从png头部读取值，并且结果将在任何情况下始终被字节交换损坏，不管它所运行的系统如何。在一个不同字节顺序的系统上读取它并不会神奇地改变png文件中的原始字节，而且由于BinaryReader明确规定在不同字节顺序的系统上不改变其行为，那一侧也不会发生变化。 - Nyerguds var buff = new byte[32];
using (var d = File.OpenRead(file))
{
d.Read(buff, 0, 32);
}
const int wOff = 16;
const int hOff = 20;
var Widht =BitConverter.ToInt32(new[] {buff[wOff + 3], buff[wOff + 2], buff[wOff + 1], buff[wOff + 0],},0);
var Height =BitConverter.ToInt32(new[] {buff[hOff + 3], buff[hOff + 2], buff[hOff + 1], buff[hOff + 0],},0);
是的，你绝对可以做到这个，代码取决于文件格式。我为一家图像供应商（Atalasoft）工作，我们的产品为每个编解码器提供了一个GetImageInfo()函数，该函数最少执行并获取尺寸和其他易于获取的数据。
如果您想自己开发，请从 wotsit.org 开始，该网站有几乎所有图像格式的详细规范，您将看到如何识别文件以及可以在其中找到信息的位置。
如果您熟悉使用 C 语言，那么也可以使用免费的jpeglib来获取此信息。我敢打赌，使用.NET库也可以实现此功能，但我不知道如何做。
new AtalaImage(filepath).Width 可以做类似的事情，这样做是否安全呢？ - drzausAtalasoft.Imaging.Codec.RegisteredDecoders.GetImageInfo(fullPath).Size - drzaus这将取决于文件格式。通常它们会在文件的早期字节中声明。而且，通常一个良好的图像读取实现会考虑到这一点。但是我无法为.NET指出一个。