blocks|key|2704909|text|我发现IPP函数是存在的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2704910|ippiRGBToYCbCr420_8u_C3P2R|offset|length|2704911|很难找到它，因为函数名或描述没有提到NV12。|2704912|该函数使用BT.601标准。|2704913|以下是在BT.601标准中将RGB转换为NV12的代码示例：|style|BOLD|2704914|void+Rgb2NV12(const+unsigned+char+I[],+int+image_width,+int+image_height,+unsigned+char+J[])
{
++++IppStatus+ipp_status;
++++int+srcStep+=+image_width*3;
++++int+dstYStep+=+image_width;
++++int+dstCbCrStep+=+image_width;
++++IppiSize+roiSize+=+{image_width,+image_height};

++++const+Ipp8u*+pSrc+=+(Ipp8u*)I;

++++Ipp8u+*pDstY++++=+(Ipp8u*)J;++++++++++++++++++++++++++++//Y+color+plane+is+the+first+image_width*image_height+pixels+of+J.
++++Ipp8u+*pDstCbCr+=+(Ipp8u*)&J[image_width*image_height];+//In+NV12+format,+UV+plane+starts+below+Y.

++++ipp_status+=+ippiRGBToYCbCr420_8u_C3P2R(pSrc,+srcStep,+pDstY,+dstYStep,+pDstCbCr,+dstCbCrStep,+roiSize);

++++//if+(ipp_status+!=+ippStsNoErr),+Handle+errors...++++++++++
}|code-block|syntax|javascript|2704915|2704916|2704917|2704918|使用BT.709标准将RGB转换为NV12的：|2704919|至于2019年，BT.709+(HDTV)标准可能比BT.601+(SDTV)更相关。|2704920|在BT.709标准中，IPP缺乏从RGB到NV12的直接转换功能。|2704921|有一个函数可以将BGR转换为NV12。|2704922|该解决方案包括两个阶段：|2704923|2704924|从RGB转换为BGR+(交换通道)。|ordered-list-item|2704925|2704926|代码示例使用ippiSwapChannels_8u_C3R进行RGB到BGR的转换。|CODE|2704927|从BGR转换为NV12。|unordered-list-item|2704928|2704929|代码示例使用ippiBGRToYCbCr420_709CSC_8u_C3P2R进行BGR到NV12的转换。|2704930|sample函数需要一些额外的内存空间来存储中间的BGR图像。|2704931|指向草图内存的指针被传递给函数(内存应该在函数外部分配)。|2704932|以下是在+to中将RGB转换为NV12的代码示例。709标准：|2704933|//sketch_buff+-+Temporary+buffer+for+storing+image+in+BGR+format.
//++++++++++++++Size+of+sketch_buff+must+be+at+least+image_width*image_height*3+bytes.
void+Rgb2NV12_709(const+unsigned+char+I[],
++++++++++++++++++const+int+image_width,+
++++++++++++++++++const+int+image_height,
++++++++++++++++++unsigned+char+sketch_buff[],
++++++++++++++++++unsigned+char+J[])
{
++++IppStatus+ipp_status;++++
++++int+srcStep+=+image_width*3;
++++int+dstBgrStep+=+image_width*3;
++++int+dstYStep+=+image_width;
++++int+dstCbCrStep+=+image_width;
++++IppiSize+roiSize+=+{image_width,+image_height};

++++const+Ipp8u*+pRGB+=+(Ipp8u*)I;
++++Ipp8u*+pBGR+=+(Ipp8u*)sketch_buff;+//BGR+image+is+stored+in+sketch_buff
++++Ipp8u+*pDstY++++=+(Ipp8u*)J;++++++++++++++++++++++++++++//Y+color+plane+is+the+first+image_width*image_height+pixels+of+J.
++++Ipp8u+*pDstCbCr+=+(Ipp8u*)&J[image_width*image_height];+//In+NV12+format,+UV+plane+starts+below+Y.

++++const+int+bgrOrder[3]+=+{2,+1,+0};

++++//Swap+Red+and+Blue+color+channels+-+convert+from+RGB+to+BGR
++++//Store+the+result+into+sketch_buff+(sketch+buffer+is+allocated+outside+the+function)
++++ipp_status+=+ippiSwapChannels_8u_C3R(pRGB,+srcStep,+pBGR,+dstBgrStep,+roiSize,+bgrOrder);

++++//if+(ipp_status+!=+ippStsNoErr),+Handle+errors...

++++//Convert+BGR+to+NV12+in+BT.709+standard
++++ipp_status+=+ippiBGRToYCbCr420_709CSC_8u_C3P2R(pBGR,+srcStep,+pDstY,+dstYStep,+pDstCbCr,+dstCbCrStep,+roiSize);

++++//if+(ipp_status+!=+ippStsNoErr),+Handle+errors...
}|2704934|entityMap|0|LINK|mutability|MUTABLE|url|https://software.intel.com/en-us/node/503959|1|https://software.intel.com/en-us/ipp-dev-reference-swapchannels|2|https://software.intel.com/en-us/ipp-dev-reference-bgrtoycbcr420-709csc^0|0|0|Q|0|0|0|0|4|6|E|3|K|4|0|0|0|0|0|M|1|0|0|0|8|3|E|4|0|0|0|1|3|7|3|0|0|6|N|V|3|Z|3|6|N|1|0|1|3|7|4|0|0|6|X|15|3|19|4|6|X|2|0|0|0|4|O|0|0^^$0|@$1|2|3|4|5|6|7|23|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|24|8|@]|9|@$D|25|E|26|1|27]]|A|$]]|$1|F|3|G|5|6|7|28|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|29|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|2A|8|@$D|2B|E|2C|L|M]|$D|2D|E|2E|L|M]|$D|2F|E|2G|L|M]]|9|@]|A|$]]|$1|N|3|O|5|P|7|2H|8|@]|9|@]|A|$Q|R]]|$1|S|3|-4|5|6|7|2I|8|@]|9|@]|A|$]]|$1|T|3|-4|5|6|7|2J|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|2K|8|@]|9|@]|A|$]]|$1|V|3|W|5|6|7|2L|8|@$D|2M|E|2N|L|M]]|9|@]|A|$]]|$1|X|3|Y|5|6|7|2O|8|@]|9|@]|A|$]]|$1|Z|3|10|5|6|7|2P|8|@]|9|@]|A|$]]|$1|11|3|12|5|6|7|2Q|8|@$D|2R|E|2S|L|M]|$D|2T|E|2U|L|M]]|9|@]|A|$]]|$1|13|3|14|5|6|7|2V|8|@]|9|@]|A|$]]|$1|15|3|-4|5|6|7|2W|8|@]|9|@]|A|$]]|$1|16|3|17|5|18|7|2X|8|@$D|2Y|E|2Z|L|M]|$D|30|E|31|L|M]]|9|@]|A|$]]|$1|19|3|-4|5|6|7|32|8|@]|9|@]|A|$]]|$1|1A|3|1B|5|6|7|33|8|@$D|34|E|35|L|1C]|$D|36|E|37|L|M]|$D|38|E|39|L|M]]|9|@$D|3A|E|3B|1|3C]]|A|$]]|$1|1D|3|1E|5|1F|7|3D|8|@$D|3E|E|3F|L|M]|$D|3G|E|3H|L|M]]|9|@]|A|$]]|$1|1G|3|-4|5|6|7|3I|8|@]|9|@]|A|$]]|$1|1H|3|1I|5|6|7|3J|8|@$D|3K|E|3L|L|1C]|$D|3M|E|3N|L|M]|$D|3O|E|3P|L|M]]|9|@$D|3Q|E|3R|1|3S]]|A|$]]|$1|1J|3|1K|5|6|7|3T|8|@]|9|@]|A|$]]|$1|1L|3|1M|5|6|7|3U|8|@]|9|@]|A|$]]|$1|1N|3|1O|5|6|7|3V|8|@$D|3W|E|3X|L|M]]|9|@]|A|$]]|$1|1P|3|1Q|5|P|7|3Y|8|@]|9|@]|A|$Q|R]]|$1|1R|3|-4|5|6|7|3Z|8|@]|9|@]|A|$]]]|1S|$1T|$5|1U|1V|1W|A|$1X|1Y]]|1Z|$5|1U|1V|1W|A|$1X|20]]|21|$5|1U|1V|1W|A|$1X|22]]]]

I found out that IPP function exists:

<a href="https://software.intel.com/en-us/node/503959" rel="nofollow noreferrer">ippiRGBToYCbCr420_8u_C3P2R</a>

It was hard to find, because the function name or description does not mention NV12. 
The function uses BT.601 standard. 

Here is a code sample for converting RGB to NV12 in BT.601 standard: 

<pre><code>void Rgb2NV12(const unsigned char I[], int image_width, int image_height, unsigned char J[])
{
 IppStatus ipp_status;
 int srcStep = image_width*3;
 int dstYStep = image_width;
 int dstCbCrStep = image_width;
 IppiSize roiSize = {image_width, image_height};

 const Ipp8u* pSrc = (Ipp8u*)I;

 Ipp8u *pDstY = (Ipp8u*)J; //Y color plane is the first image_width*image_height pixels of J.
 Ipp8u *pDstCbCr = (Ipp8u*)&amp;J[image_width*image_height]; //In NV12 format, UV plane starts below Y.

 ipp_status = ippiRGBToYCbCr420_8u_C3P2R(pSrc, srcStep, pDstY, dstYStep, pDstCbCr, dstCbCrStep, roiSize);

 //if (ipp_status != ippStsNoErr), Handle errors... 
}
</code></pre>

<hr>

<hr>

<hr>

Converting RGB to NV12 with BT.709 standard: 

As for 2019, BT.709 (HDTV) standard is probably more relevant than BT.601 (SDTV). 

IPP lacks a function for direct conversion from RGB to NV12 in BT.709 standard. 
There is a function that converts BGR to NV12. 
The solution includes two stages: 

<ol>
<li>Convert from RGB to BGR (swap channels). 
Code sample uses <a href="https://software.intel.com/en-us/ipp-dev-reference-swapchannels" rel="nofollow noreferrer"><code>ippiSwapChannels_8u_C3R</code></a> for RGB to BGR conversion. </li>
<li>Convert from BGR to NV12. 
Code sample uses <a href="https://software.intel.com/en-us/ipp-dev-reference-bgrtoycbcr420-709csc" rel="nofollow noreferrer"><code>ippiBGRToYCbCr420_709CSC_8u_C3P2R</code></a> for BGR to NV12 conversion. </li>
</ol>

The sample function requires some extra memory space for storing the intermediate BGR image. 
A pointer to the sketch memory is passed to the function (the memory should be allocated outside the function). 

Here is a code sample for converting RGB to NV12 in BT.709 standard: 

<pre><code>//sketch_buff - Temporary buffer for storing image in BGR format.
// Size of sketch_buff must be at least image_width*image_height*3 bytes.
void Rgb2NV12_709(const unsigned char I[],
 const int image_width, 
 const int image_height,
 unsigned char sketch_buff[],
 unsigned char J[])
{
 IppStatus ipp_status; 
 int srcStep = image_width*3;
 int dstBgrStep = image_width*3;
 int dstYStep = image_width;
 int dstCbCrStep = image_width;
 IppiSize roiSize = {image_width, image_height};

 const Ipp8u* pRGB = (Ipp8u*)I;
 Ipp8u* pBGR = (Ipp8u*)sketch_buff; //BGR image is stored in sketch_buff
 Ipp8u *pDstY = (Ipp8u*)J; //Y color plane is the first image_width*image_height pixels of J.
 Ipp8u *pDstCbCr = (Ipp8u*)&amp;J[image_width*image_height]; //In NV12 format, UV plane starts below Y.

 const int bgrOrder[3] = {2, 1, 0};

 //Swap Red and Blue color channels - convert from RGB to BGR
 //Store the result into sketch_buff (sketch buffer is allocated outside the function)
 ipp_status = ippiSwapChannels_8u_C3R(pRGB, srcStep, pBGR, dstBgrStep, roiSize, bgrOrder);

 //if (ipp_status != ippStsNoErr), Handle errors...

 //Convert BGR to NV12 in BT.709 standard
 ipp_status = ippiBGRToYCbCr420_709CSC_8u_C3P2R(pBGR, srcStep, pDstY, dstYStep, pDstCbCr, dstCbCrStep, roiSize);

 //if (ipp_status != ippStsNoErr), Handle errors...
}
</code></pre>

Video encoders like Intel® Media SDK require NV12 video input format.

<a href="http://www.fourcc.org/yuv.php#NV12" rel="nofollow noreferrer">NV12 format</a> is YUV 4:2:0 format ordered in memory with a Y plane first, followed by packed chroma samples in interleaved UV plane.

Example: 
<code>YYYYYY</code> 
<code>YYYYYY</code> 
<code>UVUVUV</code> 

<a href="https://i.stack.imgur.com/XboNY.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/XboNY.png" alt="enter image description here"></a>

RGB color format, refers to Pixel-Order RGB (byte per pixel, lower byte is Red): 
<code>RGBRGBRGBRGBRGB</code> 
<code>RGBRGBRGBRGBRGB</code>

<a href="https://i.stack.imgur.com/y0ggj.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/y0ggj.png" alt="enter image description here"></a>

I did some Web research, and found out that regarding NV12, <a href="https://en.wikipedia.org/wiki/YUV" rel="nofollow noreferrer">YUV</a> is defined as YCbCr color space.
There are currently at least 2 possible YCbCr formats apply NV12:

<ul>
<li><a href="https://en.wikipedia.org/wiki/Rec._601" rel="nofollow noreferrer">BT.601</a> - Applies SDTV </li>
<li><a href="https://en.wikipedia.org/wiki/Rec._709" rel="nofollow noreferrer">BT.709</a> - Applies HDTV</li>
</ul>

My question is: Is there as <a href="https://software.intel.com/en-us/intel-ipp" rel="nofollow noreferrer">IPP</a> function that converts RGB color space to NV12?

How to convert RGB to NV12 color space using IPP

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