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POConfusion on YUV NV21 conversion to RGB
 

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    <p>According to <a href="http://developer.android.com/reference/android/graphics/ImageFormat.html#NV21" rel="nofollow noreferrer">http://developer.android.com/reference/android/graphics/ImageFormat.html#NV21</a>, NV21 is the default used format.</p> <p>There are quite a number of code on web regarding YUV NV21 to RGB conversion. However, when I go through the code, I doubt on the correctness of the code.</p> <p><strong>The first component V should come first, followed by first component U</strong></p> <p>According to <a href="http://msdn.microsoft.com/en-us/library/ms867704.aspx#yuvformats_420formats_12bitsperpixel" rel="nofollow noreferrer">http://wiki.videolan.org/YUV#NV21</a>, <code>NV21 is like NV12, but with U and V order reversed: it starts with V.</code> However, when I went through the code implementation</p> <ul> <li><a href="http://pastebin.com/T0my7zSc" rel="nofollow noreferrer">http://pastebin.com/T0my7zSc</a> - It assumes U comes first</li> <li><a href="https://stackoverflow.com/a/8394202/72437">https://stackoverflow.com/a/8394202/72437</a> - It assumes U comes first too</li> <li><a href="https://stackoverflow.com/a/10125048/72437">https://stackoverflow.com/a/10125048/72437</a> - It assmes U comes first too</li> </ul> <p><strong>R should be the most significant position</strong> According implementation of <code>int argb</code> in <a href="http://www.netmite.com/android/mydroid/frameworks/base/graphics/java/android/graphics/Color.java" rel="nofollow noreferrer">Color.java</a>, R suppose to be at the most significant position. However, I went through the following code implementation</p> <ul> <li><a href="http://pastebin.com/T0my7zSc" rel="nofollow noreferrer">http://pastebin.com/T0my7zSc</a> - It assumes R is in least significant position</li> <li><a href="https://stackoverflow.com/a/8394202/72437">https://stackoverflow.com/a/8394202/72437</a> - It assumes R is in least significant position</li> </ul> <p><strong>I was wondering, are they making common mistake, or I have overlooked something?</strong> </p> <p>Currently, my implementation is as follow.</p> <pre><code>public static void YUV_NV21_TO_RGB(int[] argb, byte[] yuv, int width, int height) { final int frameSize = width * height; final int ii = 0; final int ij = 0; final int di = +1; final int dj = +1; int a = 0; for (int i = 0, ci = ii; i &lt; height; ++i, ci += di) { for (int j = 0, cj = ij; j &lt; width; ++j, cj += dj) { int y = (0xff &amp; ((int) yuv[ci * width + cj])); int v = (0xff &amp; ((int) yuv[frameSize + (ci &gt;&gt; 1) * width + (cj &amp; ~1) + 0])); int u = (0xff &amp; ((int) yuv[frameSize + (ci &gt;&gt; 1) * width + (cj &amp; ~1) + 1])); y = y &lt; 16 ? 16 : y; int r = (int) (1.164f * (y - 16) + 1.596f * (v - 128)); int g = (int) (1.164f * (y - 16) - 0.813f * (v - 128) - 0.391f * (u - 128)); int b = (int) (1.164f * (y - 16) + 2.018f * (u - 128)); r = r &lt; 0 ? 0 : (r &gt; 255 ? 255 : r); g = g &lt; 0 ? 0 : (g &gt; 255 ? 255 : g); b = b &lt; 0 ? 0 : (b &gt; 255 ? 255 : b); argb[a++] = 0xff000000 | (r &lt;&lt; 16) | (g &lt;&lt; 8) | b; } } } </code></pre>
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    1. COFor me your code works perfectly, actually is the only one that doesn't alter any of the picture properties (like brightness or colors).
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    2. COin many android functions that take a color argument, or return a color as int, they return with R being most significant so its 0xAARRGGBB, however in the actual memory layout of an android bitmap when you use JNI and access in C/C++ bytes directly, it's reversed with R being the first byte in memory and you get 0xAABBGGRR.
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