有没有一种便宜的方法来获取图像的尺寸（jpg，png，...）？最好，我想仅使用标准类库来实现这一点（因为托管限制）。我知道读取图像标题并自己解析它应该相对容易，但似乎这样的东西应该已经存在了。另外，我已经验证以下代码可以读取整个图像（我不想要）：
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);
}
}
}
一如既往，最好的选择是找到一个经过良好测试的库。然而，你说这很困难，所以这里有一些基本上未经测试的狡猾代码，应该适用于相当多的情况：
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，请将其添加到
imageFormatDecodersusing (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;
}
}
将
validateImageDatafalse您是否尝试过使用 WPF Imaging 类？
System.Windows.Media.Imaging.BitmapDecoder我相信需要付出一些努力来确保这些编解码器仅读取文件的子集以确定标头信息。值得一试。
几个月前我一直在寻找类似的东西。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，对于 GIF，所有必需的信息都在前 10 个字节中：
Type: Bytes 0-2
Version: Bytes 3-5
Height: Bytes 6-7
Width: Bytes 8-9
PNG 稍微复杂一些（宽度和高度各为 4 字节）：
Width: Bytes 16-19
Height: Bytes 20-23
如上所述，wotsit 是一个提供图像和数据格式详细规范的好网站，尽管 pnglib 的 PNG 规范要详细得多。但是，我认为关于 PNG 和 GIF 格式的维基百科条目是最好的起点。
这是我检查 GIF 的原始代码，我还为 PNG 拼凑了一些代码：
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);
}
}
根据到目前为止的答案和一些额外的搜索，似乎在 .NET 2 类库中没有它的功能。所以我决定自己写。这是它的一个非常粗糙的版本。目前，我只需要 JPG。这样就完成了阿巴斯发布的答案。
没有错误检查或任何其他验证，但我目前需要它来完成有限的任务，并且最终可以轻松添加它。我在一些图像上进行了测试，它通常不会从图像中读取超过 6K 的内容。我想这取决于 EXIF 数据量。
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);
}
}
}
}
更新了 ICR 的答案以支持渐进式 jPegs 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);
}
}
我为 PNG 文件做了这个
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，您绝对可以做到这一点，代码取决于文件格式。我为一家图像供应商工作（Atalasoft），我们的产品为每个编解码器提供了 GetImageInfo()，它可以最少地找出尺寸和其他一些易于获取的数据。
如果您想自己动手，我建议从 wotsit.org 开始，它包含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在哪里可以找到其中的信息。
如果您习惯使用 C，那么也可以使用免费的 jpeglib 来获取此信息。我敢打赌您可以使用 .NET 库来做到这一点，但我不知道如何做。
Wpf 类
System.Windows.Media.Imaging.BitmapDecoder感谢Atosk的回答。为了您的方便，这是我编辑的代码：
public static class QuickImgSize
{
public static void GetDimensions(string path, out int width, out int height)
{
using (var imageStream = File.OpenRead(path))
{
var decoder = BitmapDecoder.Create(imageStream, BitmapCreateOptions.IgnoreColorProfile,
BitmapCacheOption.Default);
height = decoder.Frames[0].PixelHeight;
width = decoder.Frames[0].PixelWidth;
}
}
}
用途：
QuickImgSize.GetDimensions(@"E:\Test\4_0.png", out var width, out var height);
这取决于文件格式。通常他们会在文件的前字节中说明这一点。通常，良好的图像读取实现会考虑到这一点。但我无法向您指出 .NET 的一个。