blocks|key|1750326|text|你有没有试过使用WPF+Imaging类？System.Windows.Media.Imaging.BitmapDecoder等？|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1750327|我相信一些努力是为了确保这些编解码器只读取文件的一个子集，以便确定头部信息。值得一查。|1750328|entityMap^0|L|16|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|M|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|N|8|@]|D|@]|E|$]]]|I|$]]

Have you tried using the WPF Imaging classes? <code>System.Windows.Media.Imaging.BitmapDecoder</code>, etc.?

I believe some effort was into making sure those codecs only read a subset of the file in order to determine header information. It's worth a check.

blocks|key|1750341|text|这将取决于文件格式。通常他们会在文件的前几个字节中声明它。通常，一个好的图像读取实现会考虑到这一点。不过，我不能为你指出.NET的一个。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1750342|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

It's going to depend on the file format. Usually they will state it up in the early bytes of the file. And, usually, a good image-reading implementation will take that into account. I can't point you to one for .NET though.

blocks|key|1535465|text|是的，你完全可以做到这一点，代码取决于文件格式。我在一家成像供应商(Atalasoft)工作，我们的产品为每个编解码器提供了一个GetImageInfo()，它最小限度地查找维度和其他一些容易获得的数据。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1535466|如果你想创建自己的文件，我建议从wotsit.org开始，它有几乎所有图像格式的详细规范，你将看到如何识别文件以及在哪里可以找到信息。|1535467|如果你习惯于使用C，那么免费的jpeglib也可以用来获取这些信息。我敢打赌，你可以用.NET库做到这一点，但我不知道怎么做。|1535468|entityMap|0|LINK|mutability|MUTABLE|url|http://www.atalasoft.com/|1|http://wotsit.org/^0|Y|9|0|0|G|A|1|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@$A|S|B|T|1|U]]|C|$]]|$1|D|3|E|5|6|7|V|8|@]|9|@$A|W|B|X|1|Y]]|C|$]]|$1|F|3|G|5|6|7|Z|8|@]|9|@]|C|$]]|$1|H|3|-4|5|6|7|10|8|@]|9|@]|C|$]]]|I|$J|$5|K|L|M|C|$N|O]]|P|$5|K|L|M|C|$N|Q]]]]

Yes, you can absolutely do this and the code depends on the file format. I work for an imaging vendor (<a href="http://www.atalasoft.com" rel="nofollow noreferrer">Atalasoft</a>), and our product provides a GetImageInfo() for every codec that does the minimum to find out dimensions and some other easy to get data.

If you want to roll your own, I suggest starting with <a href="http://wotsit.org" rel="nofollow noreferrer">wotsit.org</a>, which has detailed specs for pretty much all image formats and you will see how to identify the file and also where information in it can be found.

If you are comfortable working with C, then the free jpeglib can be used to get this information too. I would bet that you can do this with .NET libraries, but I don't know how.

blocks|key|1535493|text|几个月前我也在寻找类似的东西。我想阅读GIF图片的类型、版本、高度和宽度，但在网上找不到任何有用的东西。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1535494|幸运的是，在GIF中，所有必需的信息都在前10个字节中：|1535495|Type:+Bytes+0-2
Version:+Bytes+3-5
Height:+Bytes+6-7
Width:+Bytes+8-9|code-block|syntax|javascript|1535496|PNG稍微复杂一些(宽度和高度都是4字节)：|1535497|Width:+Bytes+16-19
Height:+Bytes+20-23|1535498|如上所述，wotsit是一个很好的关于图像和数据格式的详细规范的网站，尽管pnglib上的PNG规范要详细得多。然而，我认为关于PNG和GIF格式的维基百科条目是最好的起点。|offset|length|1535499|这是我检查GIF的原始代码，我也为PNG拼凑了一些东西：|1535500|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]+%7C+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]+%7C+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%2B%2B)
++++++++{
++++++++++++width+=+bytes[i]+%7C+width+<<+8;
++++++++++++height+=+bytes[i+%2B+4]+%7C+height+<<+8;++++++++++++
++++++++}

++++++++Console.WriteLine("PNG\nWidth:+{0}\nHeight:+{1}\n",+width,+height);++
++++}
}|1535501|entityMap|0|LINK|mutability|MUTABLE|url|http://www.wotsit.org/|1|http://www.libpng.org/pub/png/spec/1.1/PNG-Contents.html|2|https://en.wikipedia.org/wiki/Portable_Network_Graphics|3|http://en.wikipedia.org/wiki/Graphics_Interchange_Format^0|0|0|0|0|0|5|6|0|11|6|1|1S|3|2|1W|3|3|0|0|0^^$0|@$1|2|3|4|5|6|7|18|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|19|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|1A|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|1B|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|1C|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|1D|8|@]|9|@$O|1E|P|1F|1|1G]|$O|1H|P|1I|1|1J]|$O|1K|P|1L|1|1M]|$O|1N|P|1O|1|1P]]|A|$]]|$1|Q|3|R|5|6|7|1Q|8|@]|9|@]|A|$]]|$1|S|3|T|5|F|7|1R|8|@]|9|@]|A|$G|H]]|$1|U|3|-4|5|6|7|1S|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11]]|12|$5|X|Y|Z|A|$10|13]]|14|$5|X|Y|Z|A|$10|15]]|16|$5|X|Y|Z|A|$10|17]]]]

I was looking for something similar a few months earlier. I wanted to read the type, version, height and width of a GIF image but couldn’t find anything useful online.

Fortunately in case of GIF, all the required information was in the first 10 bytes:

<pre><code>Type: Bytes 0-2
Version: Bytes 3-5
Height: Bytes 6-7
Width: Bytes 8-9
</code></pre>

PNG are slightly more complex (width and height are 4-bytes each):

<pre><code>Width: Bytes 16-19
Height: Bytes 20-23
</code></pre>

As mentioned above, <a href="http://www.wotsit.org/" rel="nofollow noreferrer">wotsit</a> is a good site for detailed specs on image and data formats though the PNG specs at <a href="http://www.libpng.org/pub/png/spec/1.1/PNG-Contents.html" rel="nofollow noreferrer">pnglib</a> are much more detailed. However, I think the Wikipedia entry on <a href="https://en.wikipedia.org/wiki/Portable_Network_Graphics" rel="nofollow noreferrer">PNG</a> and <a href="http://en.wikipedia.org/wiki/Graphics_Interchange_Format" rel="nofollow noreferrer">GIF</a> formats is the best place to start.

Here’s my original code for checking GIFs, I have also slapped together something for PNGs:

<pre class="lang-cs prettyprint-override"><code>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&amp;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&amp;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] &lt;&lt; 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] &lt;&lt; 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 &lt;= 3; i++)
 {
 width = bytes[i] | width &lt;&lt; 8;
 height = bytes[i + 4] | height &lt;&lt; 8; 
 }

 Console.WriteLine("PNG\nWidth: {0}\nHeight: {1}\n", width, height); 
 }
}
</code></pre>

blocks|key|1750457|text|一如既往，你最好的办法就是找到一个经过良好测试的库。然而，您说这很困难，所以这里有一些不可靠的、基本上未经测试的代码，它们应该可以在相当多的情况下工作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1750458|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+%2B=+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%2B=+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+%2B=+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+%2B=+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);
++++++++}
++++}
}|code-block|syntax|javascript|1750459|希望代码是相当明显的。要添加新的文件格式，您可以将其添加到imageFormatDecoders中，关键字是出现在给定格式的每个文件开头的“魔术位”数组，值是从流中提取大小的函数。大多数格式都很简单，唯一令人讨厌的是jpeg。|offset|length|style|CODE|1750460|entityMap^0|0|0|T|J|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Your best bet as always is to find a well tested library. However, you said that is difficult, so here is some dodgy largely untested code that should work for a fair number of cases:

<pre><code>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&lt;byte[], Func&lt;BinaryReader, Size&gt;&gt; imageFormatDecoders = new Dictionary&lt;byte[], Func&lt;BinaryReader, Size&gt;&gt;()
 {
 { 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 },
 };

 /// &lt;summary&gt;
 /// Gets the dimensions of an image.
 /// &lt;/summary&gt;
 /// &lt;param name="path"&gt;The path of the image to get the dimensions of.&lt;/param&gt;
 /// &lt;returns&gt;The dimensions of the specified image.&lt;/returns&gt;
 /// &lt;exception cref="ArgumentException"&gt;The image was of an unrecognized format.&lt;/exception&gt;
 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;
 }
 }
 }
 }

 /// &lt;summary&gt;
 /// Gets the dimensions of an image.
 /// &lt;/summary&gt;
 /// &lt;param name="path"&gt;The path of the image to get the dimensions of.&lt;/param&gt;
 /// &lt;returns&gt;The dimensions of the specified image.&lt;/returns&gt;
 /// &lt;exception cref="ArgumentException"&gt;The image was of an unrecognized format.&lt;/exception&gt; 
 public static Size GetDimensions(BinaryReader binaryReader)
 {
 int maxMagicBytesLength = imageFormatDecoders.Keys.OrderByDescending(x =&gt; x.Length).First().Length;

 byte[] magicBytes = new byte[maxMagicBytesLength];

 for (int i = 0; i &lt; 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 &lt; 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 &lt; 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 &lt; 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);
 }
 }
}
</code></pre>

Hopefully the code is fairly obvious. To add a new file format you add it to <code>imageFormatDecoders</code> with the key being an array of the "magic bits" which appear at the beginning of every file of the given format and the value being a function which extracts the size from the stream. Most formats are simple enough, the only real stinker is jpeg.

blocks|key|1750523|text|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。所以我决定写我自己的。这是它的一个非常粗略的版本。目前，我只需要JPG的答案，所以它完成了Abbas发布的答案。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1750524|没有错误检查或任何其他验证，但我目前需要它用于有限的任务，并且它最终可以很容易地添加。我在一些图像上测试了它，它通常不会从图像中读取超过6K的内容。我猜这取决于EXIF数据量。|1750525|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+%7C%7C+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+%7C+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+%7C+data[2];
++++++++++++++++++++++++height+=+data[3]+<<+8+%7C+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+%2B+":+"+%2B+w+%2B+"+x+"+%2B+h);
++++++++++++}
++++++++}

++++}
}|code-block|syntax|javascript|1750526|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Based on the answers so far and some additional searching, it seems that in the .NET 2 class library there is no functionality for it. So I decided to write my own. Here is a very rough version of it. At the moment, I needed it only for JPG’s. So it completes the answer posted by Abbas.

There is no error checking or any other verification, but I currently need it for a limited task, and it can be eventually easily added. I tested it on some number of images, and it usually does not read more that 6K from an image. I guess it depends on the amount of the EXIF data.

<pre><code>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 &lt;&lt; 8 | lenLo) - 2;
 break;
 }

 // EOF?
 if (type == 0xD9)
 eof = true;

 // process the data
 if (len &gt; 0)
 {

 // read the data
 byte[] data = reader.ReadBytes(len);

 // this is what we are looking for
 if (type == 0xC0)
 {
 width = data[1] &lt;&lt; 8 | data[2];
 height = data[3] &lt;&lt; 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);
 }
 }

 }
}
</code></pre>

blocks|key|1750579|text|using+(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;
+++++}
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1750580|将validateImageData设置为false可防止GDI%2B对图像数据执行成本高昂的分析，从而大大缩短加载时间。This+question在这个问题上提供了更多的信息。|unstyled|offset|length|style|CODE|1750581|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/420337/validateimagedata-parameter-and-image-fromstream^0|0|1|H|L|5|1N|D|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|T|8|@$G|U|H|V|I|J]|$G|W|H|X|I|J]]|9|@$G|Y|H|Z|1|10]]|A|$]]|$1|K|3|-4|5|F|7|11|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

<pre><code>using (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;
 }
}
</code></pre>

the <code>validateImageData</code> set to <code>false</code> prevents GDI+ from performing costly analysis of the image data, thus severely decreasing load time. <a href="https://stackoverflow.com/questions/420337/validateimagedata-parameter-and-image-fromstream">This question</a> sheds more light on the subject.

blocks|key|1750601|text|我这样做是为了PNG文件。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1750602|++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+%2B+3],+buff[wOff+%2B+2],+buff[wOff+%2B+1],+buff[wOff+%2B+0],},0);
++++++++var+Height+=BitConverter.ToInt32(new[]+{buff[hOff+%2B+3],+buff[hOff+%2B+2],+buff[hOff+%2B+1],+buff[hOff+%2B+0],},0);|code-block|syntax|javascript|1750603|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I did this for PNG file 

<pre><code> 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);
</code></pre>

blocks|key|1535769|text|更新了ICR的答案，以支持渐进式jPegs和WebP+:)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1535770|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+%2B=+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+%2B=+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+%2B=+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+%2B=+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+%7C%7C+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+%2B+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);
++++}

}|code-block|syntax|javascript|1535771|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Updated ICR's answer to support progressive jPegs &amp; WebP as well :)

<pre><code>internal static class ImageHelper
{
 const string errorMessage = "Could not recognise image format.";

 private static Dictionary&lt;byte[], Func&lt;BinaryReader, Size&gt;&gt; imageFormatDecoders = new Dictionary&lt;byte[], Func&lt;BinaryReader, Size&gt;&gt;()
 {
 { 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 },
 };

 /// &lt;summary&gt; 
 /// Gets the dimensions of an image. 
 /// &lt;/summary&gt; 
 /// &lt;param name="path"&gt;The path of the image to get the dimensions of.&lt;/param&gt; 
 /// &lt;returns&gt;The dimensions of the specified image.&lt;/returns&gt; 
 /// &lt;exception cref="ArgumentException"&gt;The image was of an unrecognised format.&lt;/exception&gt; 
 public static Size GetDimensions(BinaryReader binaryReader)
 {
 int maxMagicBytesLength = imageFormatDecoders.Keys.OrderByDescending(x =&gt; x.Length).First().Length;
 byte[] magicBytes = new byte[maxMagicBytesLength];
 for(int i = 0; i &lt; 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 &lt; 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 &lt; 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 &lt; 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 &lt; 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() &amp; 0b00_11111111111111; // 14 bits width
 var height = binaryReader.ReadUInt16() &amp; 0b00_11111111111111; // 14 bits height

 return new Size(width, height);
 }

}
</code></pre>

Is there a cheap way to get the dimensions of an image (jpg, png, ...)? Preferably, I would like to achieve this using only the standard class library (because of hosting restrictions). I know that it should be relatively easy to read the image header and parse it myself, but it seems that something like this should be already there. Also, I’ve verified that the following piece of code reads the entire image (which I don’t want):

<pre><code>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);
 }
 }
}
</code></pre>

Getting image dimensions without reading the entire file

Windows

有没有便宜的方法来获取图片的尺寸(jpg，png，...)？最好是只使用标准类库(因为托管限制)来实现这一点。我知道读取图像头部并自己解析它应该相对容易，但看起来像这样的东西应该已经存在了。此外，我还验证了以下代码读取了整个图像(我不想要这样的图像)：using System;using System.Drawing;...

问无需读取整个文件即可获取图像尺寸
EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问无需读取整个文件即可获取图像尺寸EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问无需读取整个文件即可获取图像尺寸
EN