blocks|key|610056|text|C标准中没有标准库来读取文件格式.|type|unstyled|depth|inlineStyleRanges|entityRanges|data|610057|但是，大多数程序，特别是linux平台上的程序，都使用相同的库来解码图像格式：|610058|对于jpeg，它是libjpeg，对于png，它是libpng。|610059|libs已经安装的可能性非常高。|610060|http://www.libpng.org|offset|length|610061|http://www.ijg.org|610062|entityMap|0|LINK|mutability|MUTABLE|url|http://www.libpng.org/|1|http://www.ijg.org/^0|0|0|0|0|0|L|0|0|0|I|1|0^^$0|@$1|2|3|4|5|6|7|X|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Y|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Z|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|10|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|11|8|@]|9|@$J|12|K|13|1|14]]|A|$]]|$1|L|3|M|5|6|7|15|8|@]|9|@$J|16|K|17|1|18]]|A|$]]|$1|N|3|-4|5|6|7|19|8|@]|9|@]|A|$]]]|O|$P|$5|Q|R|S|A|$T|U]]|V|$5|Q|R|S|A|$T|W]]]]

There is no standard library in the C-standard to read the file-formats.

However, most programs, especially on the linux platform use the same library to decode the image-formats: 

For jpeg it's libjpeg, for png it's libpng. 

The chances that the libs are already installed is very high.

<a href="http://www.libpng.org" rel="noreferrer">http://www.libpng.org</a>

<a href="http://www.ijg.org" rel="noreferrer">http://www.ijg.org</a>

blocks|key|2140217|text|对于jpeg，已经有一个名为利比伯的库，还有用于png的利布平。好消息是，它们在其中编译，因此目标机器将不需要dll文件或任何东西。坏消息是他们在C区：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|2140218|另外，你自己也不要想到试着读+档案。如果您想要一种易于阅读的格式，请改用百万分率。|2140219|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Libjpeg|1|http://www.libpng.org/pub/png/libpng.html|2|http://en.wikipedia.org/wiki/Jpeg#Discrete_cosine_transform|3|http://en.wikipedia.org/wiki/DEFLATE#Encoder_.2F_Compressor|4|http://en.wikipedia.org/wiki/Portable_pixmap^0|E|3|0|S|3|1|0|B|3|2|F|2|3|10|4|4|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@$A|W|B|X|1|Y]|$A|Z|B|10|1|11]]|C|$]]|$1|D|3|E|5|6|7|12|8|@]|9|@$A|13|B|14|1|15]|$A|16|B|17|1|18]|$A|19|B|1A|1|1B]]|C|$]]|$1|F|3|-4|5|6|7|1C|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]|N|$5|I|J|K|C|$L|O]]|P|$5|I|J|K|C|$L|Q]]|R|$5|I|J|K|C|$L|S]]|T|$5|I|J|K|C|$L|U]]]]

For jpeg, there is already a library called <a href="http://en.wikipedia.org/wiki/Libjpeg" rel="noreferrer">libjpeg</a>, and there is <a href="http://www.libpng.org/pub/png/libpng.html" rel="noreferrer">libpng</a> for png. The good news is that they compile right in and so target machines will not need dll files or anything. The bad news is they are in C :(

Also, don't even think of <a href="http://en.wikipedia.org/wiki/Jpeg#Discrete_cosine_transform" rel="noreferrer">trying to read</a> <a href="http://en.wikipedia.org/wiki/DEFLATE#Encoder_.2F_Compressor" rel="noreferrer">the files</a> yourself. If you want an easy-to-read format, use <a href="http://en.wikipedia.org/wiki/Portable_pixmap" rel="noreferrer">PPM</a> instead.

blocks|key|610181|text|不幸的是，jpeg格式被压缩了，所以在读取单个像素之前，您必须解压缩它。这是一项非常重要的任务。如果您不能使用库，您可能需要参考一个库来查看它是如何解压缩映像的。在sourceforge上有一个开源库：CImg在sourceforge上|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|610182|entityMap|0|LINK|mutability|MUTABLE|url|http://cimg.sourceforge.net/reference/group__cimg__tutorial.html^0|2T|H|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

Unfortunately, jpeg format is compressed, so you would have to decompress it before reading individual pixels. This is a non-trivial task. If you can't use a library, you may want to refer to one to see how it's decompressing the image. There is an open-source library on sourceforge: <a href="http://cimg.sourceforge.net/reference/group__cimg__tutorial.html" rel="nofollow noreferrer">CImg on sourceforge.</a>

blocks|key|839381|text|这是我从10年前的源代码中挖掘出来的一个小例程(使用libjpeg)：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|839382|#include+<jpeglib.h>

int+loadJpg(const+char*+Name)+{
++unsigned+char+a,+r,+g,+b;
++int+width,+height;
++struct+jpeg_decompress_struct+cinfo;
++struct+jpeg_error_mgr+jerr;

++FILE+*+infile;++++++++/*+source+file+*/
++JSAMPARRAY+pJpegBuffer;+++++++/*+Output+row+buffer+*/
++int+row_stride;+++++++/*+physical+row+width+in+output+buffer+*/
++if+((infile+=+fopen(Name,+"rb"))+==+NULL)+{
++++fprintf(stderr,+"can't+open+%25s\n",+Name);
++++return+0;
++}
++cinfo.err+=+jpeg_std_error(&jerr);
++jpeg_create_decompress(&cinfo);
++jpeg_stdio_src(&cinfo,+infile);
++(void)+jpeg_read_header(&cinfo,+TRUE);
++(void)+jpeg_start_decompress(&cinfo);
++width+=+cinfo.output_width;
++height+=+cinfo.output_height;

++unsigned+char+*+pDummy+=+new+unsigned+char+[width*height*4];
++unsigned+char+*+pTest+=+pDummy;
++if+(!pDummy)+{
++++printf("NO+MEM+FOR+JPEG+CONVERT!\n");
++++return+0;
++}
++row_stride+=+width+*+cinfo.output_components;
++pJpegBuffer+=+(*cinfo.mem->alloc_sarray)
++++((j_common_ptr)+&cinfo,+JPOOL_IMAGE,+row_stride,+1);

++while+(cinfo.output_scanline+<+cinfo.output_height)+{
++++(void)+jpeg_read_scanlines(&cinfo,+pJpegBuffer,+1);
++++for+(int+x+=+0;+x+<+width;+x%2B%2B)+{
++++++a+=+0;+//+alpha+value+is+not+supported+on+jpg
++++++r+=+pJpegBuffer[0][cinfo.output_components+*+x];
++++++if+(cinfo.output_components+>+2)+{
++++++++g+=+pJpegBuffer[0][cinfo.output_components+*+x+%2B+1];
++++++++b+=+pJpegBuffer[0][cinfo.output_components+*+x+%2B+2];
++++++}+else+{
++++++++g+=+r;
++++++++b+=+r;
++++++}
++++++*(pDummy%2B%2B)+=+b;
++++++*(pDummy%2B%2B)+=+g;
++++++*(pDummy%2B%2B)+=+r;
++++++*(pDummy%2B%2B)+=+a;
++++}
++}
++fclose(infile);
++(void)+jpeg_finish_decompress(&cinfo);
++jpeg_destroy_decompress(&cinfo);

++BMap+=+(int*)pTest;+
++Height+=+height;
++Width+=+width;
++Depth+=+32;
}|code-block|syntax|javascript|839383|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|$]]

This is a small routine I digged from 10 year old source code (using libjpeg):

<pre><code>#include &lt;jpeglib.h&gt;

int loadJpg(const char* Name) {
 unsigned char a, r, g, b;
 int width, height;
 struct jpeg_decompress_struct cinfo;
 struct jpeg_error_mgr jerr;

 FILE * infile; /* source file */
 JSAMPARRAY pJpegBuffer; /* Output row buffer */
 int row_stride; /* physical row width in output buffer */
 if ((infile = fopen(Name, "rb")) == NULL) {
 fprintf(stderr, "can't open %s\n", Name);
 return 0;
 }
 cinfo.err = jpeg_std_error(&amp;jerr);
 jpeg_create_decompress(&amp;cinfo);
 jpeg_stdio_src(&amp;cinfo, infile);
 (void) jpeg_read_header(&amp;cinfo, TRUE);
 (void) jpeg_start_decompress(&amp;cinfo);
 width = cinfo.output_width;
 height = cinfo.output_height;

 unsigned char * pDummy = new unsigned char [width*height*4];
 unsigned char * pTest = pDummy;
 if (!pDummy) {
 printf("NO MEM FOR JPEG CONVERT!\n");
 return 0;
 }
 row_stride = width * cinfo.output_components;
 pJpegBuffer = (*cinfo.mem-&gt;alloc_sarray)
 ((j_common_ptr) &amp;cinfo, JPOOL_IMAGE, row_stride, 1);

 while (cinfo.output_scanline &lt; cinfo.output_height) {
 (void) jpeg_read_scanlines(&amp;cinfo, pJpegBuffer, 1);
 for (int x = 0; x &lt; width; x++) {
 a = 0; // alpha value is not supported on jpg
 r = pJpegBuffer[0][cinfo.output_components * x];
 if (cinfo.output_components &gt; 2) {
 g = pJpegBuffer[0][cinfo.output_components * x + 1];
 b = pJpegBuffer[0][cinfo.output_components * x + 2];
 } else {
 g = r;
 b = r;
 }
 *(pDummy++) = b;
 *(pDummy++) = g;
 *(pDummy++) = r;
 *(pDummy++) = a;
 }
 }
 fclose(infile);
 (void) jpeg_finish_decompress(&amp;cinfo);
 jpeg_destroy_decompress(&amp;cinfo);

 BMap = (int*)pTest; 
 Height = height;
 Width = width;
 Depth = 32;
}
</code></pre>

blocks|key|2140320|text|我对DevIL库有过很好的体验。它支持广泛的图像格式，并遵循一种非常类似于OpenGL的函数样式。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|2140321|诚然，这是一个图书馆，但绝对值得一试。|2140322|entityMap|0|LINK|mutability|MUTABLE|url|http://openil.sourceforge.net/^0|2|5|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]]|C|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]]]

I've had good experiences with the <a href="http://openil.sourceforge.net/" rel="nofollow noreferrer">DevIL</a> library. It supports a wide range of image formats and follows a function-style very similar to OpenGL. 

Granted, it is a library, but it's definitely worth a try.

blocks|key|839404|text|由于它可以使用公开，我将提到另一个库来调查：IM工具包，它托管在Sourceforge上。它是跨平台的，将文件格式与用户完全分离，允许加载和处理图像，而无需担心大多数细节。它确实支持PNG和JPEG的开箱即用，如果需要，还可以使用其他导入过滤器进行扩展。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|839405|它还配有大量的图像处理操作符.|839406|它还具有良好的质量绑定到Lua。|839407|entityMap|0|LINK|mutability|MUTABLE|url|http://www.tecgraf.puc-rio.br/im|1|http://sourceforge.net/projects/imtoolkit/|2|http://www.lua.org/^0|M|5|0|W|B|1|0|0|C|3|2|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@$A|U|B|V|1|W]|$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|6|7|10|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|11|8|@]|9|@$A|12|B|13|1|14]]|C|$]]|$1|H|3|-4|5|6|7|15|8|@]|9|@]|C|$]]]|I|$J|$5|K|L|M|C|$N|O]]|P|$5|K|L|M|C|$N|Q]]|R|$5|K|L|M|C|$N|S]]]]

Since it could use the exposure, I'll mention one other library to investigate: <a href="http://www.tecgraf.puc-rio.br/im" rel="nofollow noreferrer">The IM Toolkit</a>, which is hosted at <a href="http://sourceforge.net/projects/imtoolkit/" rel="nofollow noreferrer">Sourceforge</a>. It is cross platform, and abstracts the file format completely away from the user, allowing an image to be loaded and processed without worrying about most of the details. It does support both PNG and JPEG out of the box, and can be extended with other import filters if needed.

It comes with a large collection of image processing operators as well...

It also has a good quality binding to <a href="http://www.lua.org/" rel="nofollow noreferrer">Lua</a>.

blocks|key|610326|text|由于其他答案已经提到您将很可能需要使用库，请查看一下ImageMagick，看看是否有可能完成您需要它做的事情。它提供了各种不同的方法来与ImageMagick的核心功能进行接口，包括为几乎每一种可用的编程语言提供库。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|610327|主页：ImageMagick|610328|entityMap|0|LINK|mutability|MUTABLE|url|http://www.imagemagick.org/script/index.php|1^0|Q|B|0|0|3|B|1|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@$A|P|B|Q|1|R]]|C|$]]|$1|D|3|E|5|6|7|S|8|@]|9|@$A|T|B|U|1|V]]|C|$]]|$1|F|3|-4|5|6|7|W|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]|N|$5|I|J|K|C|$L|M]]]]

Since the other answers already mention that you will most likely need to use a library, take a look at <a href="http://www.imagemagick.org/script/index.php" rel="nofollow noreferrer">ImageMagick</a> and see if it is possible to do what you need it to do. It comes with a variety of different ways to interface with the core functionality of ImageMagick, including libraries for almost every single programming language available.
Homepage: <a href="http://www.imagemagick.org/script/index.php" rel="nofollow noreferrer">ImageMagick</a>

blocks|key|839467|text|正如Nils所指出的，没有C或C%2B%2B标准库可用于JPEG压缩和图像处理。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|839468|如果您能够使用第三方库，您可能需要尝试GDAL，它支持JPEG、PNG和其他数十种格式、压缩和媒体。|offset|length|839469|下面是一个简单的示例，介绍如何使用GDAL从C%2B%2B文件中读取像素数据：|839470|#include+<gdal_priv.h>
#include+<cassert>
#include+<iostream>
#include+<string>
#include+<vector>

int+main()
{
++++GDALAllRegister();+//+once+per+application

++++//+Assume+3-band+image+with+8-bit+per+pixel+per+channel+(24-bit+depth)
++++std::string+const+file("/home/mloskot/test.jpg");

++++//+Open+file+with+image+data
++++GDALDataset*+ds+=+static_cast<GDALDataset*>(GDALOpen(file.c_str(),+GA_ReadOnly));
++++assert(0+!=+ds);

++++//+Example+1+-+Read+multiple+bands+at+once,+assume+8-bit+depth+per+band
++++{
++++++++int+const+ncols+=+ds->GetRasterXSize();
++++++++int+const+nrows+=+ds->GetRasterYSize();
++++++++int+const+nbands+=+ds->GetRasterCount();
++++++++int+const+nbpp+=+GDALGetDataTypeSize(GDT_Byte)+/+8;
++++++++std::vector<unsigned+char>+data(ncols+*+nrows+*+nbands+*+nbpp);

++++++++CPLErr+err+=+ds->RasterIO(GF_Read,+0,+0,+ncols,+nrows,+&data[0],+ncols,+nrows,+GDT_Byte,+nbands,+0,+0,+0,+0);
++++++++assert(CE_None+==+err);

++++++++//+...+use+data
++++}

++++//+Example+2+-+Read+first+scanline+by+scanline+of+1+band+only,+assume+8-bit+depth+per+band
++++{
++++++++GDALRasterBand*+band1+=+ds->GetRasterBand(1);
++++++++assert(0+!=+band1);

++++++++int+const+ncols+=+band1->GetXSize();
++++++++int+const+nrows+=+band1->GetYSize();
++++++++int+const+nbpp+=+GDALGetDataTypeSize(GDT_Byte)+/+8;
++++++++std::vector<unsigned+char>+scanline(ncols+*+nbpp);

++++++++for+(int+i+=+0;+i+<+nrows;+%2B%2Bi)
++++++++{
++++++++++++CPLErr+err+=+band1->RasterIO(GF_Read,+0,+0,+ncols,+1,+&scanline[0],+ncols,+1,+GDT_Byte,+0,+0);
++++++++++++assert(CE_None+==+err);

++++++++++++//+...+use+scanline
++++++++}
++++}

++++return+0;
}|code-block|syntax|javascript|839471|还有更完整的GDAL教程可用。|839472|entityMap|0|LINK|mutability|MUTABLE|url|https://gdal.org/|1|https://gdal.org/tutorials/raster_api_tut.html^0|0|J|4|0|0|0|0|6|6|1|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Z|8|@]|9|@$D|10|E|11|1|12]]|A|$]]|$1|F|3|G|5|6|7|13|8|@]|9|@]|A|$]]|$1|H|3|I|5|J|7|14|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|15|8|@]|9|@$D|16|E|17|1|18]]|A|$]]|$1|O|3|-4|5|6|7|19|8|@]|9|@]|A|$]]]|P|$Q|$5|R|S|T|A|$U|V]]|W|$5|R|S|T|A|$U|X]]]]

As Nils pointed, there is no such thing as a C or C++ standard library for JPEG compression and image manipulation.
In case you'd be able to use a third party library, you may want to try <a href="https://gdal.org/" rel="nofollow noreferrer">GDAL</a> which supports JPEG, PNG and tens of other formats, compressions and mediums.
Here is simple example that presents how to read pixel data from JPEG file using GDAL C++ API:
<pre><code>#include &lt;gdal_priv.h&gt;
#include &lt;cassert&gt;
#include &lt;iostream&gt;
#include &lt;string&gt;
#include &lt;vector&gt;

int main()
{
 GDALAllRegister(); // once per application

 // Assume 3-band image with 8-bit per pixel per channel (24-bit depth)
 std::string const file(&quot;/home/mloskot/test.jpg&quot;);

 // Open file with image data
 GDALDataset* ds = static_cast&lt;GDALDataset*&gt;(GDALOpen(file.c_str(), GA_ReadOnly));
 assert(0 != ds);

 // Example 1 - Read multiple bands at once, assume 8-bit depth per band
 {
 int const ncols = ds-&gt;GetRasterXSize();
 int const nrows = ds-&gt;GetRasterYSize();
 int const nbands = ds-&gt;GetRasterCount();
 int const nbpp = GDALGetDataTypeSize(GDT_Byte) / 8;
 std::vector&lt;unsigned char&gt; data(ncols * nrows * nbands * nbpp);

 CPLErr err = ds-&gt;RasterIO(GF_Read, 0, 0, ncols, nrows, &amp;data[0], ncols, nrows, GDT_Byte, nbands, 0, 0, 0, 0);
 assert(CE_None == err);

 // ... use data
 }

 // Example 2 - Read first scanline by scanline of 1 band only, assume 8-bit depth per band
 {
 GDALRasterBand* band1 = ds-&gt;GetRasterBand(1);
 assert(0 != band1);

 int const ncols = band1-&gt;GetXSize();
 int const nrows = band1-&gt;GetYSize();
 int const nbpp = GDALGetDataTypeSize(GDT_Byte) / 8;
 std::vector&lt;unsigned char&gt; scanline(ncols * nbpp);

 for (int i = 0; i &lt; nrows; ++i)
 {
 CPLErr err = band1-&gt;RasterIO(GF_Read, 0, 0, ncols, 1, &amp;scanline[0], ncols, 1, GDT_Byte, 0, 0);
 assert(CE_None == err);

 // ... use scanline
 }
 }

 return 0;
}
</code></pre>
There is more complete <a href="https://gdal.org/tutorials/raster_api_tut.html" rel="nofollow noreferrer">GDAL API tutorial</a> available.

blocks|key|839480|text|，如果速度不是问题，，您可以尝试采用非常简约的方法加载和保存PNG的LodePNG。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|839481|甚至可以使用函数中的自包含png加载程序的同一个作者的picoPNG。|839482|entityMap|0|LINK|mutability|MUTABLE|url|http://members.gamedev.net/lode/projects/LodePNG/^0|0|A|Y|7|0|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]]|D|@$9|S|A|T|1|U]]|E|$]]|$1|F|3|G|5|6|7|V|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|W|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

If speed is not a problem you can try <a href="http://members.gamedev.net/lode/projects/LodePNG/" rel="nofollow">LodePNG</a> that take a very minimalist approach to PNG loading and saving.

Or even go with picoPNG from the same author that is a self-contained png loader in a function.

I'm doing some image processing, and I'd like to individually read each pixel value in a JPEG and PNG images.

In my deployment scenario, it would be awkward for me to use a 3rd party library (as I have restricted access on the target computer), but I'm assuming that there's no standard C or C++ library for reading JPEG/PNG...

So, if you know of a way of not using a library then great, if not then answers are still welcome!

How do I read JPEG and PNG pixels in C++ on Linux?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我正在做一些图像处理，我想单独读取JPEG和PNG图像中的每个像素值。在我的部署场景中，如果我使用第三方库(因为我限制了目标计算机上的访问权限)，我会感到很尴尬，但是我假设没有标准的C或C++库来读取JPEG/PNG.所以，如果你知道一种不使用库的方法，那就太好了，如果不是，答案仍然是受欢迎的！

问如何在Linux上读取C++中的JPEG和PNG像素？
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问如何在Linux上读取C++中的JPEG和PNG像素？EN