YUV格式初探

作者: 我心若氺 | 来源:发表于2018-01-19 14:20 被阅读486次

一、 YUV起源

二、 YUV的类型

一、YUV起源

常见的颜色模型中，RGB主要用于电子系统里表达和显示颜色，CMYK印刷四色模式用于彩色印刷，而YUV是被欧洲电视系统所采用的一种颜色编码方法。

使用YUV的优点有两个:

一.YUV主要用于优化彩色视频信号的传输，使其向后兼容老式黑白电视，这一特性用在于电视信号上。

二.YUV是数据总尺寸小于RGB格式（但用YUV444的话，和RGB888一样都是24bits）

彩色，Y分量，V分量，U分量

二、YUV的类型

YUV细分的话有Y'UV，YUV，YCbCr，YPbPr等类型，其中YCbCr主要用于数字信号.

YCbCr 是在世界数字组织视频标准研制过程中作为ITU - R BT1601 建议的一部分, 其实是YUV经过Gamma的翻版。其中Y与YUV 中的Y含义一致, Cb , Cr 同样都指色彩, 只是在表示方法上不同而已。在YUV 家族中, YCbCr 是在计算机系统中应用最多的成员, 其应用领域很广泛,JPEG、MPEG，H264均采用此格式。

其中，Cr反映了RGB输入信号红色部分与RGB信号亮度值之间的差异，而Cb反映的是RGB输入信号蓝色部分与RGB信号亮度值之间的差异，此即所谓的色差信号

一般所讲的YUV大多是指YCbCr。以下用YUV指代YCbCr。

图像生成RGB分量与YUV分量

三、YUV的采样和存储格式

采样

YUV的采样有许多种，常用的有444，422，420，411等。

用三个图来直观地表示采集的方式吧，以黑点表示采样该像素点的Y分量，以空心圆圈表示采用该像素点的UV分量。

YUV常用采样

1.YUV 4:4:4采样，每一个Y对应一组UV分量。
· 4:4:4 Formats, 24 Bits per Pixel
2.YUV 4:2:2采样，每两个Y共用一组UV分量。
· 4:2:2 Formats, 16 Bits per Pixel
3.YUV 4:2:0采样，每四个Y共用一组UV分量。
· 4:2:0 Formats, 12 Bits per Pixel

4:4:4 means no downsampling of the chroma channels.

4:2:2 means 2:1 horizontal downsampling, with no vertical downsampling. Every scan line contains four Y samples for every two U or V samples.

4:2:0 means 2:1 horizontal downsampling, with 2:1 vertical downsampling.

4:1:1 means 4:1 horizontal downsampling, with no vertical downsampling. Every scan line contains four Y samples for every U or V sample. 
4:1:1 sampling is less common than other formats, and is not discussed in detail in this article.

存储

YUV的存储格式有两大类：packed和planar，还有SemiPlanar。

对于packed的YUV格式，每个像素点的Y,U,V是连续交错存储的。

对于planar的YUV格式，先连续存储所有像素点的Y，紧接着存储所有像素点的U，随后是所有像素点的V。

对于SemiPlanar，则是先连续存储所有像素点的Y，再连续交错U和V。

根据不同的摆放顺序有如下几种常见的：

Packed方式

UYVY422（COLOR_FormatYUV422PackedPlanar）

其他的VYUY422，YUYV422，YVYU422只不过是数据矩阵中Y,U,V顺序差别:

VYUY422：  V1 Y1 U1 Y2  V2 Y3 U2 Y4 ...

YUYV422(YUY2)： Y1 U1 Y2 V1   Y3 U2 Y4 V2 ...

YVYU422：  Y1 V1 Y2 U1    Y3 V2 Y4 U2 …

UYVY422

YUV420 Packet(COLOR_FormatYUV420PackedPlanar) 如下:
YUV420 packet每2X2的Y分量公用一个UV分量，并且将YUV打包到一个平面，如图所示

YUV420 Packet

Planar和SemiPlanar方式

YUV422P（COLOR_FormatYUV422Planar） 如下:
每两个连续的Y分量公用一个UV空间，Y分量空间后面跟U分量平面，然后为V分量平面

YUV422P

YUV422SP（COLOR_FormatYUV422SemiPlanar） 如下：
每两个连续的Y分量公用一个UV空间，前面是Y分量空间，后面是U，V交错分量平面

YUV422SP

YUV420P（COLOR_FormatYUV420Planar） 如下：

YUV420P

YUV420SP（ COLOR_FormatYUV420SemiPlanar） 如下：

YUV420SP

其中YUV420P和YUV420SP根据U、V的顺序，又可分出2种格式。

YUV420P：U前V后即YUV420P，也叫I420，

V前U后，叫YV12(YV表示Y后面跟着V，12表示12bit)。

YUV420SP：U前V后叫NV12，

V前U后叫NV21。

数据排列如下:

I420: YYYYYYYY UU VV =>YUV420P

YV12: YYYYYYYY VV UU =>YUV420P

NV12: YYYYYYYY UVUV =>YUV420SP

NV21: YYYYYYYY VUVU =>YUV420SP

四、YUV的相关Enum

OpenNI2的原生像素格式定义如下：

typedef enum

{

// Depth

ONI_PIXEL_FORMAT_DEPTH_1_MM = 100,

ONI_PIXEL_FORMAT_DEPTH_100_UM = 101,

ONI_PIXEL_FORMAT_SHIFT_9_2 = 102,

ONI_PIXEL_FORMAT_SHIFT_9_3 = 103,

// Color

ONI_PIXEL_FORMAT_RGB888 = 200,

ONI_PIXEL_FORMAT_YUV422 = 201,

ONI_PIXEL_FORMAT_GRAY8 = 202,

ONI_PIXEL_FORMAT_GRAY16 = 203,

ONI_PIXEL_FORMAT_JPEG = 204,

ONI_PIXEL_FORMAT_YUYV = 205,

} OniPixelFormat;

AstraSDK的像素格式定义如下：

typedef enum {

    ASTRA_PIXEL_FORMAT_UNKNOWN = 0,

    ASTRA_PIXEL_FORMAT_DEPTH_MM = 100,

    // color layouts

    ASTRA_PIXEL_FORMAT_RGB888 = 200,

    ASTRA_PIXEL_FORMAT_YUV422 = 201,

    ASTRA_PIXEL_FORMAT_YUYV = 202,

    ASTRA_PIXEL_FORMAT_RGBA = 203,

    ASTRA_PIXEL_FORMAT_GRAY8 = 300,

    ASTRA_PIXEL_FORMAT_GRAY16 = 301,

    ASTRA_PIXEL_FORMAT_POINT = 400,

} astra_pixel_formats;

LINUX_VIDEODEV2(V4L2)的相关定义如下：

#define V4L2_PIX_FMT_YYUV    v4l2_fourcc('Y','Y','U','V') /* 16  YUV 4:2:2     */

#define V4L2_PIX_FMT_YUYV    v4l2_fourcc('Y','U','Y','V') /* 16  YUV 4:2:2     */

#define V4L2_PIX_FMT_UYVY    v4l2_fourcc('U','Y','V','Y') /* 16  YUV 4:2:2     */

#define V4L2_PIX_FMT_YUV422P v4l2_fourcc('4','2','2','P') /* 16  YVU422 planar */

#define V4L2_PIX_FMT_NV12    v4l2_fourcc('N','V','1','2') /* 12  Y/CbCr 4:2:0  */

#define V4L2_PIX_FMT_NV21    v4l2_fourcc('N','V','2','1') /* 12  Y/CrCb 4:2:0  */

#define V4L2_PIX_FMT_YVU420  v4l2_fourcc('Y','V','1','2') /* 12  YVU 4:2:0     */

#define V4L2_PIX_FMT_YUV420  v4l2_fourcc('Y','U','1','2') /* 12  YUV 4:2:0     */

微软的YUV Video Subtypes相关定义如下：

GUID	Format	Sampling	Packed or planar	Bits per channel
MEDIASUBTYPE_AYUV	AYUV	4:4:4	Packed	8
MEDIASUBTYPE_YUY2	YUY2	4:2:2	Packed	8
MEDIASUBTYPE_UYVY	UYVY	4:2:2	Packed	8
MEDIASUBTYPE_IMC1	IMC1	4:2:0	Planar	8
MEDIASUBTYPE_IMC3	IMC2	4:2:0	Planar	8
MEDIASUBTYPE_IMC2	IMC3	4:2:0	Planar	8
MEDIASUBTYPE_IMC4	IMC4	4:2:0	Planar	8
MEDIASUBTYPE_YV12	YV12	4:2:0	Planar	8
MEDIASUBTYPE_NV12	NV12	4:2:0	Planar	8

Android API的MediaCodecInfo.CodecCapabilities如下：

int COLOR_Format12bitRGB444
This constant was deprecated in API level 23. Use COLOR_Format24bitBGR888.  
int COLOR_Format16bitARGB1555
This constant was deprecated in API level 23. Use COLOR_Format32bitABGR8888.    
int COLOR_Format16bitARGB4444
This constant was deprecated in API level 23. Use COLOR_Format32bitABGR8888.    
int COLOR_Format16bitBGR565
This constant was deprecated in API level 23. Use COLOR_Format16bitRGB565.  
int COLOR_Format16bitRGB565
16 bits per pixel RGB color format, with 5-bit red & blue and 6-bit green component.    
int COLOR_Format18BitBGR666
This constant was deprecated in API level 23. Use COLOR_Format24bitBGR888.  
int COLOR_Format18bitARGB1665
This constant was deprecated in API level 23. Use COLOR_Format32bitABGR8888.    
int COLOR_Format18bitRGB666
This constant was deprecated in API level 23. Use COLOR_Format24bitBGR888.  
int COLOR_Format19bitARGB1666
This constant was deprecated in API level 23. Use COLOR_Format32bitABGR8888.    
int COLOR_Format24BitABGR6666
This constant was deprecated in API level 23. Use COLOR_Format32bitABGR8888.    
int COLOR_Format24BitARGB6666
This constant was deprecated in API level 23. Use COLOR_Format32bitABGR8888.    
int COLOR_Format24bitARGB1887
This constant was deprecated in API level 23. Use COLOR_Format32bitABGR8888.    
int COLOR_Format24bitBGR888
24 bits per pixel RGB color format, with 8-bit red, green & blue components.    
int COLOR_Format24bitRGB888
This constant was deprecated in API level 23. Use COLOR_Format24bitBGR888 or COLOR_FormatRGBFlexible.   
int COLOR_Format25bitARGB1888
This constant was deprecated in API level 23. Use COLOR_Format32bitABGR8888.    
int COLOR_Format32bitABGR8888
32 bits per pixel RGBA color format, with 8-bit red, green, blue, and alpha components. 
int COLOR_Format32bitARGB8888
This constant was deprecated in API level 23. Use COLOR_Format32bitABGR8888 Or COLOR_FormatRGBAFlexible.    
int COLOR_Format32bitBGRA8888
This constant was deprecated in API level 23. Use COLOR_Format32bitABGR8888 Or COLOR_FormatRGBAFlexible.    
int COLOR_Format8bitRGB332
This constant was deprecated in API level 23. Use COLOR_Format24bitBGR888.  
int COLOR_FormatCbYCrY
This constant was deprecated in API level 23. Use COLOR_FormatYUV422Flexible.   
int COLOR_FormatCrYCbY
This constant was deprecated in API level 23. Use COLOR_FormatYUV422Flexible.   
int COLOR_FormatL16
16 bits per pixel, little-endian Y color format.    
int COLOR_FormatL2
This constant was deprecated in API level 23. Use COLOR_FormatL8.   
int COLOR_FormatL24
This constant was deprecated in API level 23. Use COLOR_FormatL16.  
int COLOR_FormatL32
This constant was deprecated in API level 23. Use COLOR_FormatL16.  
int COLOR_FormatL4
This constant was deprecated in API level 23. Use COLOR_FormatL8.   
int COLOR_FormatL8
8 bits per pixel Y color format.    
int COLOR_FormatMonochrome
This constant was deprecated in API level 23. Use COLOR_Format24bitBGR888.  
int COLOR_FormatRGBAFlexible
Flexible 32 bits per pixel RGBA color format with 8-bit red, green, blue, and alpha components. 
int COLOR_FormatRGBFlexible
Flexible 24 bits per pixel RGB color format with 8-bit red, green and blue components.  
int COLOR_FormatRawBayer10bit
SMIA 10-bit Bayer format.   
int COLOR_FormatRawBayer8bit
SMIA 8-bit Bayer format.    
int COLOR_FormatRawBayer8bitcompressed
SMIA 8-bit compressed Bayer format. 
int COLOR_FormatSurface 
int COLOR_FormatYCbYCr
This constant was deprecated in API level 23. Use COLOR_FormatYUV422Flexible.   
int COLOR_FormatYCrYCb
This constant was deprecated in API level 23. Use COLOR_FormatYUV422Flexible.   
int COLOR_FormatYUV411PackedPlanar
This constant was deprecated in API level 23. Use COLOR_FormatYUV420Flexible.   
int COLOR_FormatYUV411Planar
This constant was deprecated in API level 23. Use COLOR_FormatYUV420Flexible.   
int COLOR_FormatYUV420Flexible
Flexible 12 bits per pixel, subsampled YUV color format with 8-bit chroma and luma components.  
int COLOR_FormatYUV420PackedPlanar
This constant was deprecated in API level 23. Use COLOR_FormatYUV420Flexible.   
int COLOR_FormatYUV420PackedSemiPlanar
This constant was deprecated in API level 23. Use COLOR_FormatYUV420Flexible.   
int COLOR_FormatYUV420Planar
This constant was deprecated in API level 23. Use COLOR_FormatYUV420Flexible.   
int COLOR_FormatYUV420SemiPlanar
This constant was deprecated in API level 23. Use COLOR_FormatYUV420Flexible.   
int COLOR_FormatYUV422Flexible
Flexible 16 bits per pixel, subsampled YUV color format with 8-bit chroma and luma components.  
int COLOR_FormatYUV422PackedPlanar
This constant was deprecated in API level 23. Use COLOR_FormatYUV422Flexible.   
int COLOR_FormatYUV422PackedSemiPlanar
This constant was deprecated in API level 23. Use COLOR_FormatYUV422Flexible.   
int COLOR_FormatYUV422Planar
This constant was deprecated in API level 23. Use COLOR_FormatYUV422Flexible.   
int COLOR_FormatYUV422SemiPlanar
This constant was deprecated in API level 23. Use COLOR_FormatYUV422Flexible.   
int COLOR_FormatYUV444Flexible
Flexible 24 bits per pixel YUV color format with 8-bit chroma and luma components.  
int COLOR_FormatYUV444Interleaved
This constant was deprecated in API level 23. Use COLOR_FormatYUV444Flexible.   
int COLOR_QCOM_FormatYUV420SemiPlanar
This constant was deprecated in API level 23. Use COLOR_FormatYUV420Flexible.   
int COLOR_TI_FormatYUV420PackedSemiPlanar
This constant was deprecated in API level 23. Use COLOR_FormatYUV420Flexible.

COLOR_FormatYUV420Flexible

这里简单谈谈COLOR_FormatYUV420Flexible，YUV420Flexible并不是一种确定的YUV420格式，而是包含COLOR_FormatYUV411Planar, COLOR_FormatYUV411PackedPlanar, COLOR_FormatYUV420Planar, COLOR_FormatYUV420PackedPlanar, COLOR_FormatYUV420SemiPlanar和COLOR_FormatYUV420PackedSemiPlanar。

在API 21引入YUV420Flexible的同时，它所包含的这些格式都deprecated掉了。

五、YUV与RGB转换

Digital Y′CbCr (8 bits per sample) is derived from analog R'G'B' as follows:

将系数都除以255以后，得到以下公式：

1. <u>RGB 转换成 YUV</u>

2. 

3. Y = (0.257 * R) + (0.504 * G) + (0.098 * B) + 16

4. 

5. Cr = V = (0.439 * R) - (0.368 * G) - (0.071 * B) + 128

6. 

7. Cb = U = -( 0.148 * R) - (0.291 * G) + (0.439 * B) + 128

8. 

9. <u>YUV 转换成 RGB</u>

10. 

11. B = 1.164(Y - 16) + 2.018(U - 128)

12. 

13. G = 1.164(Y - 16) - 0.813(V - 128) - 0.391(U - 128)

14. 

15. R = 1.164(Y - 16) + 1.596(V - 128)

这些转换都可以使用SIMD指令集（比如NEON，MMX），来提高性能。