blocks|key|332014|text|简单地说，你不能。原因是Bitmap和JPEG，PNG等一样是一种图像类型。将图像加载到位图中后，将显示位图格式的图像。没有办法查看位图并理解图像的原始编码(如果它甚至与位图不同)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|332015|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|$]]

Simply speaking you can't. The reason why is that Bitmap is a type of image in the same way that JPEG, PNG, etc are. Once you load a image into a Bitmap the image of the bitmap format. There is no way to look at a bitmap and understand the original encoding of the image (if it's even different than Bitmap).

blocks|key|3091204|text|如果想知道图像的格式，可以使用Image类加载该文件，并检查其RawFormat属性：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3091205|using(Image+img+=+Image.FromFile(@"C:\path\to\img.jpg"))
{
++++if+(img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Jpeg))
++++{
++++++//+...
++++}
}|code-block|syntax|javascript|3091206|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/system.drawing.image.aspx|1|http://msdn.microsoft.com/en-us/library/system.drawing.image.rawformat.aspx^0|F|5|0|V|9|1|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@$A|T|B|U|1|V]|$A|W|B|X|1|Y]]|C|$]]|$1|D|3|E|5|F|7|Z|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|10|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]|Q|$5|L|M|N|C|$O|R]]]]

If you want to know the format of an image, you can load the file with the <a href="http://msdn.microsoft.com/en-us/library/system.drawing.image.aspx" rel="noreferrer">Image</a> class, and check its <a href="http://msdn.microsoft.com/en-us/library/system.drawing.image.rawformat.aspx" rel="noreferrer">RawFormat</a> property:

<pre><code>using(Image img = Image.FromFile(@"C:\path\to\img.jpg"))
{
 if (img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Jpeg))
 {
 // ...
 }
}
</code></pre>

blocks|key|3091228|text|你当然可以。ImageFormat并没有多大意义。ImageCodecInfo有更多的含义。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3091229|red_dot.png|3091230|​|3091231|📷|atomic|3091232|3091233|<a+href="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==">
++++<img+src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg=="+alt="red_dot.png"+title="red_dot.png"/>
</a>|code-block|syntax|javascript|3091234|代码：|3091235|using+System.Linq;

//...

//get+image
var+file_bytes+=+System.Convert.FromBase64String(@"iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==");
var+file_stream+=+new+System.IO.MemoryStream(file_bytes);
var+file_image+=+System.Drawing.Image.FromStream(file_stream);

//list+image+formats
var+image_formats+=+typeof(System.Drawing.Imaging.ImageFormat).GetProperties(System.Reflection.BindingFlags.Public+%7C+System.Reflection.BindingFlags.Static).ToList().ConvertAll(property+=>+property.GetValue(null,+null));
System.Diagnostics.Debug.WriteLine(image_formats.Count,+"image_formats");
foreach(var+image_format+in+image_formats)+{
++++System.Diagnostics.Debug.WriteLine(image_format,+"image_formats");
}

//get+image+format
var+file_image_format+=+typeof(System.Drawing.Imaging.ImageFormat).GetProperties(System.Reflection.BindingFlags.Public+%7C+System.Reflection.BindingFlags.Static).ToList().ConvertAll(property+=>+property.GetValue(null,+null)).Single(image_format+=>+image_format.Equals(file_image.RawFormat));
System.Diagnostics.Debug.WriteLine(file_image_format,+"file_image_format");

//list+image+codecs
var+image_codecs+=+System.Drawing.Imaging.ImageCodecInfo.GetImageDecoders().ToList();
System.Diagnostics.Debug.WriteLine(image_codecs.Count,+"image_codecs");
foreach(var+image_codec+in+image_codecs)+{
++++System.Diagnostics.Debug.WriteLine(image_codec.CodecName+%2B+",+mime:+"+%2B+image_codec.MimeType+%2B+",+extension:+"+%2B+@image_codec.FilenameExtension,+"image_codecs");
}

//get+image+codec
var+file_image_format_codec+=+System.Drawing.Imaging.ImageCodecInfo.GetImageDecoders().ToList().Single(image_codec+=>+image_codec.FormatID+==+file_image.RawFormat.Guid);
System.Diagnostics.Debug.WriteLine(file_image_format_codec.CodecName+%2B+",+mime:+"+%2B+file_image_format_codec.MimeType+%2B+",+extension:+"+%2B+file_image_format_codec.FilenameExtension,+"image_codecs",+"file_image_format_type");|3091236|调试输出：|3091237|image_formats:+10
image_formats:+MemoryBMP
image_formats:+Bmp
image_formats:+Emf
image_formats:+Wmf
image_formats:+Gif
image_formats:+Jpeg
image_formats:+Png
image_formats:+Tiff
image_formats:+Exif
image_formats:+Icon
file_image_format:+Png
image_codecs:+8
image_codecs:+Built-in+BMP+Codec,+mime:+image/bmp,+extension:+*.BMP;*.DIB;*.RLE
image_codecs:+Built-in+JPEG+Codec,+mime:+image/jpeg,+extension:+*.JPG;*.JPEG;*.JPE;*.JFIF
image_codecs:+Built-in+GIF+Codec,+mime:+image/gif,+extension:+*.GIF
image_codecs:+Built-in+EMF+Codec,+mime:+image/x-emf,+extension:+*.EMF
image_codecs:+Built-in+WMF+Codec,+mime:+image/x-wmf,+extension:+*.WMF
image_codecs:+Built-in+TIFF+Codec,+mime:+image/tiff,+extension:+*.TIF;*.TIFF
image_codecs:+Built-in+PNG+Codec,+mime:+image/png,+extension:+*.PNG
image_codecs:+Built-in+ICO+Codec,+mime:+image/x-icon,+extension:+*.ICO
Built-in+PNG+Codec,+mime:+image/png,+extension:+*.PNG|3091238|entityMap|0|IMAGE|mutability|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/yehe-900000/7a6f6285f1d69e095bd1d128839ff4f6.png|imageAlt^0|6|B|P|E|0|0|0|0|1|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|19|8|@$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1E|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|1F|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|1G|8|@]|D|@$9|1H|A|1I|1|1J]]|E|$]]|$1|M|3|I|5|6|7|1K|8|@]|D|@]|E|$]]|$1|N|3|O|5|P|7|1L|8|@]|D|@]|E|$Q|R]]|$1|S|3|T|5|6|7|1M|8|@]|D|@]|E|$]]|$1|U|3|V|5|P|7|1N|8|@]|D|@]|E|$Q|R]]|$1|W|3|X|5|6|7|1O|8|@]|D|@]|E|$]]|$1|Y|3|Z|5|P|7|1P|8|@]|D|@]|E|$Q|R]]|$1|10|3|-4|5|6|7|1Q|8|@]|D|@]|E|$]]]|11|$12|$5|13|14|15|E|$16|17|18|-4]]]]

of course you can. <code>ImageFormat</code> doesn't mean much. <code>ImageCodecInfo</code> has much more meaning.

red_dot.png

<img src="https://i.stack.imgur.com/PrNbA.png" alt="red_dot.png">

<pre><code>&lt;a href="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg=="&gt;
 &lt;img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==" alt="red_dot.png" title="red_dot.png"/&gt;
&lt;/a&gt;
</code></pre>

code:

<pre><code>using System.Linq;

//...

//get image
var file_bytes = System.Convert.FromBase64String(@"iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==");
var file_stream = new System.IO.MemoryStream(file_bytes);
var file_image = System.Drawing.Image.FromStream(file_stream);

//list image formats
var image_formats = typeof(System.Drawing.Imaging.ImageFormat).GetProperties(System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Static).ToList().ConvertAll(property =&gt; property.GetValue(null, null));
System.Diagnostics.Debug.WriteLine(image_formats.Count, "image_formats");
foreach(var image_format in image_formats) {
 System.Diagnostics.Debug.WriteLine(image_format, "image_formats");
}

//get image format
var file_image_format = typeof(System.Drawing.Imaging.ImageFormat).GetProperties(System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Static).ToList().ConvertAll(property =&gt; property.GetValue(null, null)).Single(image_format =&gt; image_format.Equals(file_image.RawFormat));
System.Diagnostics.Debug.WriteLine(file_image_format, "file_image_format");

//list image codecs
var image_codecs = System.Drawing.Imaging.ImageCodecInfo.GetImageDecoders().ToList();
System.Diagnostics.Debug.WriteLine(image_codecs.Count, "image_codecs");
foreach(var image_codec in image_codecs) {
 System.Diagnostics.Debug.WriteLine(image_codec.CodecName + ", mime: " + image_codec.MimeType + ", extension: " + @image_codec.FilenameExtension, "image_codecs");
}

//get image codec
var file_image_format_codec = System.Drawing.Imaging.ImageCodecInfo.GetImageDecoders().ToList().Single(image_codec =&gt; image_codec.FormatID == file_image.RawFormat.Guid);
System.Diagnostics.Debug.WriteLine(file_image_format_codec.CodecName + ", mime: " + file_image_format_codec.MimeType + ", extension: " + file_image_format_codec.FilenameExtension, "image_codecs", "file_image_format_type");
</code></pre>

debug output:

<pre><code>image_formats: 10
image_formats: MemoryBMP
image_formats: Bmp
image_formats: Emf
image_formats: Wmf
image_formats: Gif
image_formats: Jpeg
image_formats: Png
image_formats: Tiff
image_formats: Exif
image_formats: Icon
file_image_format: Png
image_codecs: 8
image_codecs: Built-in BMP Codec, mime: image/bmp, extension: *.BMP;*.DIB;*.RLE
image_codecs: Built-in JPEG Codec, mime: image/jpeg, extension: *.JPG;*.JPEG;*.JPE;*.JFIF
image_codecs: Built-in GIF Codec, mime: image/gif, extension: *.GIF
image_codecs: Built-in EMF Codec, mime: image/x-emf, extension: *.EMF
image_codecs: Built-in WMF Codec, mime: image/x-wmf, extension: *.WMF
image_codecs: Built-in TIFF Codec, mime: image/tiff, extension: *.TIF;*.TIFF
image_codecs: Built-in PNG Codec, mime: image/png, extension: *.PNG
image_codecs: Built-in ICO Codec, mime: image/x-icon, extension: *.ICO
Built-in PNG Codec, mime: image/png, extension: *.PNG
</code></pre>

blocks|key|332037|text|下面是我的扩展方法。希望这对某些人有帮助。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|332038|public+static+System.Drawing.Imaging.ImageFormat+GetImageFormat(this+System.Drawing.Image+img)
++++{+++++++++++++
++++++++if+(img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Jpeg))
++++++++++++return+System.Drawing.Imaging.ImageFormat.Jpeg;
++++++++if+(img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Bmp))
++++++++++++return+System.Drawing.Imaging.ImageFormat.Bmp;
++++++++if+(img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Png))
++++++++++++return+System.Drawing.Imaging.ImageFormat.Png;
++++++++if+(img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Emf))
++++++++++++return+System.Drawing.Imaging.ImageFormat.Emf;
++++++++if+(img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Exif))
++++++++++++return+System.Drawing.Imaging.ImageFormat.Exif;
++++++++if+(img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Gif))
++++++++++++return+System.Drawing.Imaging.ImageFormat.Gif;
++++++++if+(img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Icon))
++++++++++++return+System.Drawing.Imaging.ImageFormat.Icon;
++++++++if+(img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.MemoryBmp))
++++++++++++return+System.Drawing.Imaging.ImageFormat.MemoryBmp;
++++++++if+(img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Tiff))
++++++++++++return+System.Drawing.Imaging.ImageFormat.Tiff;
++++++++else
++++++++++++return+System.Drawing.Imaging.ImageFormat.Wmf;++++++++++++
++++}|code-block|syntax|javascript|332039|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|$]]

Here is my extension method. Hope this help someone.

<pre><code>public static System.Drawing.Imaging.ImageFormat GetImageFormat(this System.Drawing.Image img)
 { 
 if (img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Jpeg))
 return System.Drawing.Imaging.ImageFormat.Jpeg;
 if (img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Bmp))
 return System.Drawing.Imaging.ImageFormat.Bmp;
 if (img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Png))
 return System.Drawing.Imaging.ImageFormat.Png;
 if (img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Emf))
 return System.Drawing.Imaging.ImageFormat.Emf;
 if (img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Exif))
 return System.Drawing.Imaging.ImageFormat.Exif;
 if (img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Gif))
 return System.Drawing.Imaging.ImageFormat.Gif;
 if (img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Icon))
 return System.Drawing.Imaging.ImageFormat.Icon;
 if (img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.MemoryBmp))
 return System.Drawing.Imaging.ImageFormat.MemoryBmp;
 if (img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Tiff))
 return System.Drawing.Imaging.ImageFormat.Tiff;
 else
 return System.Drawing.Imaging.ImageFormat.Wmf; 
 }
</code></pre>

blocks|key|3304112|text|基于Alex上面的工作(我实际上投票作为解决方案，因为它只有一行-但我还不能投票哈哈)，我为图像库提出了以下函数。需要4.0|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3304113|++Public+Enum+Formats
++++Unknown
++++Bmp
++++Emf
++++Wmf
++++Gif
++++Jpeg
++++Png
++++Tiff
++++Icon
++End+Enum

++Public+Shared+Function+ImageFormat(ByVal+Image+As+System.Drawing.Image)+As+Formats
++++If+Not+System.Enum.TryParse(Of+Formats)(System.Drawing.Imaging.ImageCodecInfo.GetImageDecoders().ToList().[Single](Function(ImageCodecInfo)+ImageCodecInfo.FormatID+=+Image.RawFormat.Guid).FormatDescription,+True,+ImageFormat)+Then
++++++Return+Formats.Unknown
++++End+If
++End+Function|code-block|syntax|javascript|3304114|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|$]]

Based on Alex's work above (which I actually vote as the solution, since it's one line - but I can't vote yet haha), I came up with the following function for an image library.
It requires 4.0

<pre><code> Public Enum Formats
 Unknown
 Bmp
 Emf
 Wmf
 Gif
 Jpeg
 Png
 Tiff
 Icon
 End Enum

 Public Shared Function ImageFormat(ByVal Image As System.Drawing.Image) As Formats
 If Not System.Enum.TryParse(Of Formats)(System.Drawing.Imaging.ImageCodecInfo.GetImageDecoders().ToList().[Single](Function(ImageCodecInfo) ImageCodecInfo.FormatID = Image.RawFormat.Guid).FormatDescription, True, ImageFormat) Then
 Return Formats.Unknown
 End If
 End Function
</code></pre>

blocks|key|334360|text|这是我的代码。您必须先将完整的图像或标题(前4个字节)加载到字节数组中。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|334361|public+enum+ImageFormat
{
++++Bmp,
++++Jpeg,
++++Gif,
++++Tiff,
++++Png,
++++Unknown
}

public+static+ImageFormat+GetImageFormat(byte[]+bytes)
{
++++//+see+http://www.mikekunz.com/image_file_header.html++
++++var+bmp++++=+Encoding.ASCII.GetBytes("BM");+++++//+BMP
++++var+gif++++=+Encoding.ASCII.GetBytes("GIF");++++//+GIF
++++var+png++++=+new+byte[]+{+137,+80,+78,+71+};++++//+PNG
++++var+tiff+++=+new+byte[]+{+73,+73,+42+};+++++++++//+TIFF
++++var+tiff2++=+new+byte[]+{+77,+77,+42+};+++++++++//+TIFF
++++var+jpeg+++=+new+byte[]+{+255,+216,+255,+224+};+//+jpeg
++++var+jpeg2++=+new+byte[]+{+255,+216,+255,+225+};+//+jpeg+canon

++++if+(bmp.SequenceEqual(bytes.Take(bmp.Length)))
++++++++return+ImageFormat.Bmp;

++++if+(gif.SequenceEqual(bytes.Take(gif.Length)))
++++++++return+ImageFormat.Gif;

++++if+(png.SequenceEqual(bytes.Take(png.Length)))
++++++++return+ImageFormat.Png;

++++if+(tiff.SequenceEqual(bytes.Take(tiff.Length)))
++++++++return+ImageFormat.Tiff;

++++if+(tiff2.SequenceEqual(bytes.Take(tiff2.Length)))
++++++++return+ImageFormat.Tiff;

++++if+(jpeg.SequenceEqual(bytes.Take(jpeg.Length)))
++++++++return+ImageFormat.Jpeg;

++++if+(jpeg2.SequenceEqual(bytes.Take(jpeg2.Length)))
++++++++return+ImageFormat.Jpeg;

++++return+ImageFormat.Unknown;
}|code-block|syntax|javascript|334362|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|$]]

here is my code for this. You have to load the complete image or the header (first 4 bytes) to a byte array first.

<pre><code>public enum ImageFormat
{
 Bmp,
 Jpeg,
 Gif,
 Tiff,
 Png,
 Unknown
}

public static ImageFormat GetImageFormat(byte[] bytes)
{
 // see http://www.mikekunz.com/image_file_header.html 
 var bmp = Encoding.ASCII.GetBytes("BM"); // BMP
 var gif = Encoding.ASCII.GetBytes("GIF"); // GIF
 var png = new byte[] { 137, 80, 78, 71 }; // PNG
 var tiff = new byte[] { 73, 73, 42 }; // TIFF
 var tiff2 = new byte[] { 77, 77, 42 }; // TIFF
 var jpeg = new byte[] { 255, 216, 255, 224 }; // jpeg
 var jpeg2 = new byte[] { 255, 216, 255, 225 }; // jpeg canon

 if (bmp.SequenceEqual(bytes.Take(bmp.Length)))
 return ImageFormat.Bmp;

 if (gif.SequenceEqual(bytes.Take(gif.Length)))
 return ImageFormat.Gif;

 if (png.SequenceEqual(bytes.Take(png.Length)))
 return ImageFormat.Png;

 if (tiff.SequenceEqual(bytes.Take(tiff.Length)))
 return ImageFormat.Tiff;

 if (tiff2.SequenceEqual(bytes.Take(tiff2.Length)))
 return ImageFormat.Tiff;

 if (jpeg.SequenceEqual(bytes.Take(jpeg.Length)))
 return ImageFormat.Jpeg;

 if (jpeg2.SequenceEqual(bytes.Take(jpeg2.Length)))
 return ImageFormat.Jpeg;

 return ImageFormat.Unknown;
}
</code></pre>

blocks|key|3091330|text|根据Alex上面的发现(ImageCodecInfo.GetImageDecoders())，在Image类型上提供了几个干净的扩展方法来确定这一点。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3091331|在第一次调用之后，这是高度优化的，因为静态ImageCodecsDictionary被保存在内存中(但仅在它被使用一次之后)。|3091332|public+static+class+ImageCodecInfoX
{

++++private+static+Dictionary<Guid,+ImageCodecInfoFull>+_imageCodecsDictionary;

++++public+static+Dictionary<Guid,+ImageCodecInfoFull>+ImageCodecsDictionary+
++++{
++++++++get
++++++++{
++++++++++++if+(_imageCodecsDictionary+==+null)+{
++++++++++++++++_imageCodecsDictionary+=
++++++++++++++++++++ImageCodecInfo.GetImageDecoders()
++++++++++++++++++++.Select(i+=>+{
++++++++++++++++++++++++var+format+=+ImageFormats.Unknown;
++++++++++++++++++++++++switch+(i.FormatDescription.ToLower())+{
++++++++++++++++++++++++++++case+"jpeg":+format+=+ImageFormats.Jpeg;+break;
++++++++++++++++++++++++++++case+"png":+format+=+ImageFormats.Png;+break;
++++++++++++++++++++++++++++case+"icon":+format+=+ImageFormats.Icon;+break;
++++++++++++++++++++++++++++case+"gif":+format+=+ImageFormats.Gif;+break;
++++++++++++++++++++++++++++case+"bmp":+format+=+ImageFormats.Bmp;+break;
++++++++++++++++++++++++++++case+"tiff":+format+=+ImageFormats.Tiff;+break;
++++++++++++++++++++++++++++case+"emf":+format+=+ImageFormats.Emf;+break;
++++++++++++++++++++++++++++case+"wmf":+format+=+ImageFormats.Wmf;+break;
++++++++++++++++++++++++}
++++++++++++++++++++++++return+new+ImageCodecInfoFull(i)+{+Format+=+format+};
++++++++++++++++++++})
++++++++++++++++++++.ToDictionary(c+=>+c.CodecInfo.FormatID);
++++++++++++}
++++++++++++return+_imageCodecsDictionary;
++++++++}
++++}

++++public+static+ImageCodecInfoFull+CodecInfo(this+Image+image)
++++{
++++++++ImageCodecInfoFull+codecInfo+=+null;

++++++++if+(!ImageCodecsDictionary.TryGetValue(image.RawFormat.Guid,+out+codecInfo))
++++++++++++return+null;
++++++++return+codecInfo;
++++}

++++public+static+ImageFormats+Format(this+Image+image)
++++{
++++++++var+codec+=+image.CodecInfo();
++++++++return+codec+==+null+?+ImageFormats.Unknown+:+codec.Format;
++++}
}

public+enum+ImageFormats+{+Jpeg,+Png,+Icon,+Gif,+Bmp,+Emf,+Wmf,+Tiff,+Unknown+}

///+<summary>
///+Couples+ImageCodecInfo+with+an+ImageFormats+type.
///+</summary>
public+class+ImageCodecInfoFull
{
++++public+ImageCodecInfoFull(ImageCodecInfo+codecInfo+=+null)
++++{
++++++++Format+=+ImageFormats.Unknown;
++++++++CodecInfo+=+codecInfo;
++++}

++++public+ImageCodecInfo+CodecInfo+{+get;+set;+}

++++public+ImageFormats+Format+{+get;+set;+}

}|code-block|syntax|javascript|3091333|entityMap^0|C|X|1C|5|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|U|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|N|$]]

A couple of clean extension methods on type <code>Image</code> for determining this, based on the find by Alex above (<code>ImageCodecInfo.GetImageDecoders()</code>). 

This is highly optimized after the first call, as the static ImageCodecsDictionary is saved in memory (but only after it has been used once).

<pre><code>public static class ImageCodecInfoX
{

 private static Dictionary&lt;Guid, ImageCodecInfoFull&gt; _imageCodecsDictionary;

 public static Dictionary&lt;Guid, ImageCodecInfoFull&gt; ImageCodecsDictionary 
 {
 get
 {
 if (_imageCodecsDictionary == null) {
 _imageCodecsDictionary =
 ImageCodecInfo.GetImageDecoders()
 .Select(i =&gt; {
 var format = ImageFormats.Unknown;
 switch (i.FormatDescription.ToLower()) {
 case "jpeg": format = ImageFormats.Jpeg; break;
 case "png": format = ImageFormats.Png; break;
 case "icon": format = ImageFormats.Icon; break;
 case "gif": format = ImageFormats.Gif; break;
 case "bmp": format = ImageFormats.Bmp; break;
 case "tiff": format = ImageFormats.Tiff; break;
 case "emf": format = ImageFormats.Emf; break;
 case "wmf": format = ImageFormats.Wmf; break;
 }
 return new ImageCodecInfoFull(i) { Format = format };
 })
 .ToDictionary(c =&gt; c.CodecInfo.FormatID);
 }
 return _imageCodecsDictionary;
 }
 }

 public static ImageCodecInfoFull CodecInfo(this Image image)
 {
 ImageCodecInfoFull codecInfo = null;

 if (!ImageCodecsDictionary.TryGetValue(image.RawFormat.Guid, out codecInfo))
 return null;
 return codecInfo;
 }

 public static ImageFormats Format(this Image image)
 {
 var codec = image.CodecInfo();
 return codec == null ? ImageFormats.Unknown : codec.Format;
 }
}

public enum ImageFormats { Jpeg, Png, Icon, Gif, Bmp, Emf, Wmf, Tiff, Unknown }

/// &lt;summary&gt;
/// Couples ImageCodecInfo with an ImageFormats type.
/// &lt;/summary&gt;
public class ImageCodecInfoFull
{
 public ImageCodecInfoFull(ImageCodecInfo codecInfo = null)
 {
 Format = ImageFormats.Unknown;
 CodecInfo = codecInfo;
 }

 public ImageCodecInfo CodecInfo { get; set; }

 public ImageFormats Format { get; set; }

}
</code></pre>

blocks|key|329419|text|当我试图使用imagecodeinfo获取mime类型时，我遇到了一个奇怪的问题。对于某些png文件，guids并不完全相同...|type|unstyled|depth|inlineStyleRanges|entityRanges|data|329420|首先，我检查了ImageCodecinfo，如果代码找不到图像格式，那么我使用Matthias+Wuttke的解决方案来比较图像格式。|329421|如果上述两种解决方案都失败，则使用扩展方法获取文件的mime类型。|329422|如果mime类型更改，则文件也会更改，我们计算下载文件的校验和以匹配服务器上原始文件的校验和。所以对我们来说，获得合适的文件作为输出是很重要的。|329423|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|L|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

one weird problem i faced when i was trying to get the mime type using imagecodeinfo.. for some png files the guids were not exactly same... 

first i was checking with the ImageCodecinfo and if code does not find the imageformat then i compared the imageformat using Matthias Wuttke's solution.

if both the above mentioned solution failed then used the extension method to get the file mime type..

if the mime type changes then the file also changes, we were calculating the downloaded files checksum to match with the checksum of the original file on the server .. so for us it was importent to get proper file as output.

blocks|key|3091402|text|我不想费心去讨论这个老话题，但为了完成这个讨论，我想分享一下我对所有图像格式的查询方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3091403|using+System.Diagnostics;
using+System.Drawing;
using+System.Drawing.Imaging;

public+static+class+ImageExtentions
{
++++public+static+ImageCodecInfo+GetCodecInfo(this+System.Drawing.Image+img)
++++{
++++++++ImageCodecInfo[]+decoders+=+ImageCodecInfo.GetImageDecoders();
++++++++foreach+(ImageCodecInfo+decoder+in+decoders)
++++++++++++if+(img.RawFormat.Guid+==+decoder.FormatID)
++++++++++++++++return+decoder;
++++++++return+null;
++++}
}|code-block|syntax|javascript|3091404|现在您可以将其作为镜像扩展使用，如下所示：|3091405|public+void+Test(Image+img)
{
++++ImageCodecInfo+info+=+img.GetCodecInfo();
++++if+(info+==+null)
++++++++Trace.TraceError("Image+format+is+unkown");
++++else
++++++++Trace.TraceInformation("Image+format+is+"+%2B+info.FormatDescription);
}|3091406|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Not to bother to on old topic, but to complete this discussion, I want to share my way to query all image formats, known by windows.

<pre><code>using System.Diagnostics;
using System.Drawing;
using System.Drawing.Imaging;

public static class ImageExtentions
{
 public static ImageCodecInfo GetCodecInfo(this System.Drawing.Image img)
 {
 ImageCodecInfo[] decoders = ImageCodecInfo.GetImageDecoders();
 foreach (ImageCodecInfo decoder in decoders)
 if (img.RawFormat.Guid == decoder.FormatID)
 return decoder;
 return null;
 }
}
</code></pre>

Now you can use it as an an image extension as shown below:

<pre><code>public void Test(Image img)
{
 ImageCodecInfo info = img.GetCodecInfo();
 if (info == null)
 Trace.TraceError("Image format is unkown");
 else
 Trace.TraceInformation("Image format is " + info.FormatDescription);
}
</code></pre>

blocks|key|330983|text|Cesare+Imperiali提供的最简单的方法如下：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|330984|var+format+=+new+ImageFormat(Image.FromFile(myFile).RawFormat.Guid);|code-block|syntax|javascript|330985|但是，.jpg的.ToString()返回"ImageFormat:+b96b3cae-0728-11d3-9d7b-0000f81ef32e“而不是"Jpeg”。如果这对你很重要，这是我的解决方案：|330986|public+static+class+ImageFilesHelper
{
++++public+static+List<ImageFormat>+ImageFormats+=>
++++++++typeof(ImageFormat).GetProperties(BindingFlags.Static+%7C+BindingFlags.Public)
++++++++++.Select(p+=>+(ImageFormat)p.GetValue(null,+null)).ToList();

++++public+static+ImageFormat+ImageFormatFromRawFormat(ImageFormat+raw)+=>
++++++++ImageFormats.FirstOrDefault(f+=>+raw.Equals(f))+??+ImageFormat.Bmp;

}
//+usage:
var+format+=+ImageFilesHelper.ImageFormatFromRawFormat(Image.FromFile(myFile).RawFormat);|330987|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/users/1183309/cesare-imperiali^0|0|G|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@]|C|$]]|$1|K|3|L|5|F|7|10|8|@]|9|@]|C|$G|H]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

The simplest method was offered by <a href="https://stackoverflow.com/users/1183309/cesare-imperiali">Cesare Imperiali</a> as this:

<pre><code>var format = new ImageFormat(Image.FromFile(myFile).RawFormat.Guid);
</code></pre>

However, the .ToString() for a .jpg returns "[ImageFormat: b96b3cae-0728-11d3-9d7b-0000f81ef32e]" instead of "Jpeg". If that matters to you, here is my solution:

<pre><code>public static class ImageFilesHelper
{
 public static List&lt;ImageFormat&gt; ImageFormats =&gt;
 typeof(ImageFormat).GetProperties(BindingFlags.Static | BindingFlags.Public)
 .Select(p =&gt; (ImageFormat)p.GetValue(null, null)).ToList();

 public static ImageFormat ImageFormatFromRawFormat(ImageFormat raw) =&gt;
 ImageFormats.FirstOrDefault(f =&gt; raw.Equals(f)) ?? ImageFormat.Bmp;

}
// usage:
var format = ImageFilesHelper.ImageFormatFromRawFormat(Image.FromFile(myFile).RawFormat);
</code></pre>

blocks|key|334470|text|Agent+CK，我喜欢你的扩展方法并添加了一个字符串重载，另外我还减少了你的方法的代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|334471|public+static+class+ImageExtentions
{
++++public+static+ImageCodecInfo+GetCodecInfo(this+Image+img)+=>
++++++++ImageCodecInfo.GetImageDecoders().FirstOrDefault(decoder+=>+decoder.FormatID+==+img.RawFormat.Guid);

++++//+Note:+this+will+throw+an+exception+if+"file"+is+not+an+Image+file
++++//+quick+fix+is+a+try/catch,+but+there+are+more+sophisticated+methods
++++public+static+ImageCodecInfo+GetCodecInfo(this+string+file)
++++{
++++++++using+(var+img+=+Image.FromFile(file))
++++++++++++return+img.GetCodecInfo();
++++}
}

//+Usage:
string+file+=+@"C:\MyImage.tif";
string+description+=+$"Image+format+is+{file.GetCodecInfo()?.FormatDescription+??+"unknown"}.";
Console.WriteLine(description);|code-block|syntax|javascript|334472|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/users/8852075/agent-ck^0|0|8|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

<a href="https://stackoverflow.com/users/8852075/agent-ck">Agent CK</a>, I liked your extension method and added a string overload, plus I reduced the code for your method:

<pre><code>public static class ImageExtentions
{
 public static ImageCodecInfo GetCodecInfo(this Image img) =&gt;
 ImageCodecInfo.GetImageDecoders().FirstOrDefault(decoder =&gt; decoder.FormatID == img.RawFormat.Guid);

 // Note: this will throw an exception if "file" is not an Image file
 // quick fix is a try/catch, but there are more sophisticated methods
 public static ImageCodecInfo GetCodecInfo(this string file)
 {
 using (var img = Image.FromFile(file))
 return img.GetCodecInfo();
 }
}

// Usage:
string file = @"C:\MyImage.tif";
string description = $"Image format is {file.GetCodecInfo()?.FormatDescription ?? "unknown"}.";
Console.WriteLine(description);
</code></pre>

I am loading the binary bytes of the image file hard drive and loading it into a Bitmap object. How do i find the image type[JPEG, PNG, BMP etc] from the Bitmap object?

Looks trivial. But, couldn't figure it out!

Is there an alternative approach?

Appreciate your response.

UPDATED CORRECT SOLUTION: 

@CMS: Thanks for the correct response!

Sample code to achieve this.

<pre><code>using (MemoryStream imageMemStream = new MemoryStream(fileData))
{
 using (Bitmap bitmap = new Bitmap(imageMemStream))
 {
 ImageFormat imageFormat = bitmap.RawFormat;
 if (bitmap.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Jpeg))
 //It's a JPEG;
 else if (bitmap.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Png))
 //It's a PNG;
 }
}
</code></pre>

Find image format using Bitmap object in C#

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我正在加载图像文件硬盘驱动器的二进制字节，并将其加载到一个Bitmap对象中。如何从位图对象中找到图像typeJPEG、PNG、BMP等？看起来微不足道。但是，我想不出来！有没有其他方法？感谢您的回复。更新了正确的解决方案：@CMS:感谢您的正确回复！实现这一点的示例代码。using (MemoryStream ima...

问在C#中使用位图对象查找图像格式
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