OPENCV3.0 函数学习2——cvtColor

1 .cvtColor

cvtColor 是Opencv里的颜色空间转换函数，可以实现RGB颜色向HSV,HSI等颜色空间的转换，也可以转换为灰度图像。

函数参数说明 

void cvtColor( InputArray src, OutputArray dst, int code, int dstCn = 0 )

The function converts an input image from one color space to another. In case of a transformation
to-from RGB color space, the order of the channels should be specified explicitly (RGB or BGR). Note
that the default color format in OpenCV is often referred to as RGB but it is actually BGR (the
bytes are reversed). So the first byte in a standard (24-bit) color image will be an 8-bit Blue
component, the second byte will be Green, and the third byte will be Red. The fourth, fifth, and
sixth bytes would then be the second pixel (Blue, then Green, then Red), and so on.

The conventional ranges for R, G, and B channel values are:
-   0 to 255 for CV_8U images
-   0 to 65535 for CV_16U images
-   0 to 1 for CV_32F images

In case of linear transformations, the range does not matter. But in case of a non-linear
transformation, an input RGB image should be normalized to the proper value range to get the correct
results, for example, for RGB \f$\rightarrow\f$ L\*u\*v\* transformation. For example, if you have a
32-bit floating-point image directly converted from an 8-bit image without any scaling, then it will
have the 0..255 value range instead of 0..1 assumed by the function. So, before calling cvtColor ,
you need first to scale the image down:
@code
    img *= 1./255;
    cvtColor(img, img, COLOR_BGR2Luv);
@endcode
If you use cvtColor with 8-bit images, the conversion will have some information lost. For many
applications, this will not be noticeable but it is recommended to use 32-bit images in applications
that need the full range of colors or that convert an image before an operation and then convert
back.

If conversion adds the alpha channel, its value will set to the maximum of corresponding channel
range: 255 for CV_8U, 65535 for CV_16U, 1 for CV_32F.

@param src input image: 8-bit unsigned, 16-bit unsigned ( CV_16UC... ), or single-precision
floating-point.
@param dst output image of the same size and depth as src.
@param code color space conversion code (see cv::ColorConversionCodes).
@param dstCn number of channels in the destination image; if the parameter is 0, the number of the
channels is derived automatically from src and code. （不填，默认为0）

@see @ref imgproc_color_conversions

code  

    COLOR_BGR2BGRA     = 0, //!< add alpha channel to RGB or BGR image
    COLOR_RGB2RGBA     = COLOR_BGR2BGRA,

    COLOR_BGRA2BGR     = 1, //!< remove alpha channel from RGB or BGR image
    COLOR_RGBA2RGB     = COLOR_BGRA2BGR,

    COLOR_BGR2RGBA     = 2, //!< convert between RGB and BGR color spaces (with or without alpha channel)
    COLOR_RGB2BGRA     = COLOR_BGR2RGBA,

    COLOR_RGBA2BGR     = 3, （灰度图像）
    COLOR_BGRA2RGB     = COLOR_RGBA2BGR,

    COLOR_BGR2RGB      = 4,
    COLOR_RGB2BGR      = COLOR_BGR2RGB,

    COLOR_BGRA2RGBA    = 5,
    COLOR_RGBA2BGRA    = COLOR_BGRA2RGBA,

    COLOR_BGR2GRAY     = 6, //!< convert between RGB/BGR and grayscale, @ref color_convert_rgb_gray "color conversions"
    COLOR_RGB2GRAY     = 7,
    COLOR_GRAY2BGR     = 8,
    COLOR_GRAY2RGB     = COLOR_GRAY2BGR,
    COLOR_GRAY2BGRA    = 9,
    COLOR_GRAY2RGBA    = COLOR_GRAY2BGRA,
    COLOR_BGRA2GRAY    = 10,
    COLOR_RGBA2GRAY    = 11,

    COLOR_BGR2BGR565   = 12, //!< convert between RGB/BGR and BGR565 (16-bit images)
    COLOR_RGB2BGR565   = 13,
    COLOR_BGR5652BGR   = 14,
    COLOR_BGR5652RGB   = 15,
    COLOR_BGRA2BGR565  = 16,
    COLOR_RGBA2BGR565  = 17,
    COLOR_BGR5652BGRA  = 18,
    COLOR_BGR5652RGBA  = 19,

    COLOR_GRAY2BGR565  = 20, //!< convert between grayscale to BGR565 (16-bit images)
    COLOR_BGR5652GRAY  = 21,

    COLOR_BGR2BGR555   = 22,  //!< convert between RGB/BGR and BGR555 (16-bit images)
    COLOR_RGB2BGR555   = 23,
    COLOR_BGR5552BGR   = 24,
    COLOR_BGR5552RGB   = 25,
    COLOR_BGRA2BGR555  = 26,
    COLOR_RGBA2BGR555  = 27,
    COLOR_BGR5552BGRA  = 28,
    COLOR_BGR5552RGBA  = 29,

    COLOR_GRAY2BGR555  = 30, //!< convert between grayscale and BGR555 (16-bit images)
    COLOR_BGR5552GRAY  = 31,

    COLOR_BGR2XYZ      = 32, //!< convert RGB/BGR to CIE XYZ, @ref color_convert_rgb_xyz "color conversions"
    COLOR_RGB2XYZ      = 33,
    COLOR_XYZ2BGR      = 34,
    COLOR_XYZ2RGB      = 35,

    COLOR_BGR2YCrCb    = 36, //!< convert RGB/BGR to luma-chroma (aka YCC), @ref color_convert_rgb_ycrcb "color conversions"
    COLOR_RGB2YCrCb    = 37,
    COLOR_YCrCb2BGR    = 38,
    COLOR_YCrCb2RGB    = 39,

    COLOR_BGR2HSV      = 40, //!< convert RGB/BGR to HSV (hue saturation value), @ref color_convert_rgb_hsv "color conversions"
    COLOR_RGB2HSV      = 41,

    COLOR_BGR2Lab      = 44, //!< convert RGB/BGR to CIE Lab, @ref color_convert_rgb_lab "color conversions"
    COLOR_RGB2Lab      = 45,

    COLOR_BGR2Luv      = 50, //!< convert RGB/BGR to CIE Luv, @ref color_convert_rgb_luv "color conversions"
    COLOR_RGB2Luv      = 51,
    COLOR_BGR2HLS      = 52, //!< convert RGB/BGR to HLS (hue lightness saturation), @ref color_convert_rgb_hls "color conversions"
    COLOR_RGB2HLS      = 53,

    COLOR_HSV2BGR      = 54, //!< backward conversions to RGB/BGR
    COLOR_HSV2RGB      = 55,

    COLOR_Lab2BGR      = 56,
    COLOR_Lab2RGB      = 57,
    COLOR_Luv2BGR      = 58,
    COLOR_Luv2RGB      = 59,
    COLOR_HLS2BGR      = 60,
    COLOR_HLS2RGB      = 61,

    COLOR_BGR2HSV_FULL = 66, //!<
    COLOR_RGB2HSV_FULL = 67,
    COLOR_BGR2HLS_FULL = 68,
    COLOR_RGB2HLS_FULL = 69,

    COLOR_HSV2BGR_FULL = 70,
    COLOR_HSV2RGB_FULL = 71,
    COLOR_HLS2BGR_FULL = 72,
    COLOR_HLS2RGB_FULL = 73,

    COLOR_LBGR2Lab     = 74,
    COLOR_LRGB2Lab     = 75,
    COLOR_LBGR2Luv     = 76,
    COLOR_LRGB2Luv     = 77,

    COLOR_Lab2LBGR     = 78,
    COLOR_Lab2LRGB     = 79,
    COLOR_Luv2LBGR     = 80,
    COLOR_Luv2LRGB     = 81,

    COLOR_BGR2YUV      = 82, //!< convert between RGB/BGR and YUV
    COLOR_RGB2YUV      = 83,
    COLOR_YUV2BGR      = 84,
    COLOR_YUV2RGB      = 85,

    //! YUV 4:2:0 family to RGB
    COLOR_YUV2RGB_NV12  = 90,
    COLOR_YUV2BGR_NV12  = 91,
    COLOR_YUV2RGB_NV21  = 92,
    COLOR_YUV2BGR_NV21  = 93,
    COLOR_YUV420sp2RGB  = COLOR_YUV2RGB_NV21,
    COLOR_YUV420sp2BGR  = COLOR_YUV2BGR_NV21,

    COLOR_YUV2RGBA_NV12 = 94,
    COLOR_YUV2BGRA_NV12 = 95,
    COLOR_YUV2RGBA_NV21 = 96,
    COLOR_YUV2BGRA_NV21 = 97,
    COLOR_YUV420sp2RGBA = COLOR_YUV2RGBA_NV21,
    COLOR_YUV420sp2BGRA = COLOR_YUV2BGRA_NV21,

    COLOR_YUV2RGB_YV12  = 98,
    COLOR_YUV2BGR_YV12  = 99,
    COLOR_YUV2RGB_IYUV  = 100,
    COLOR_YUV2BGR_IYUV  = 101,
    COLOR_YUV2RGB_I420  = COLOR_YUV2RGB_IYUV,
    COLOR_YUV2BGR_I420  = COLOR_YUV2BGR_IYUV,
    COLOR_YUV420p2RGB   = COLOR_YUV2RGB_YV12,
    COLOR_YUV420p2BGR   = COLOR_YUV2BGR_YV12,

    COLOR_YUV2RGBA_YV12 = 102,
    COLOR_YUV2BGRA_YV12 = 103,
    COLOR_YUV2RGBA_IYUV = 104,
    COLOR_YUV2BGRA_IYUV = 105,
    COLOR_YUV2RGBA_I420 = COLOR_YUV2RGBA_IYUV,
    COLOR_YUV2BGRA_I420 = COLOR_YUV2BGRA_IYUV,
    COLOR_YUV420p2RGBA  = COLOR_YUV2RGBA_YV12,
    COLOR_YUV420p2BGRA  = COLOR_YUV2BGRA_YV12,

    COLOR_YUV2GRAY_420  = 106,
    COLOR_YUV2GRAY_NV21 = COLOR_YUV2GRAY_420,
    COLOR_YUV2GRAY_NV12 = COLOR_YUV2GRAY_420,
    COLOR_YUV2GRAY_YV12 = COLOR_YUV2GRAY_420,
    COLOR_YUV2GRAY_IYUV = COLOR_YUV2GRAY_420,
    COLOR_YUV2GRAY_I420 = COLOR_YUV2GRAY_420,
    COLOR_YUV420sp2GRAY = COLOR_YUV2GRAY_420,
    COLOR_YUV420p2GRAY  = COLOR_YUV2GRAY_420,

    //! YUV 4:2:2 family to RGB
    COLOR_YUV2RGB_UYVY = 107,
    COLOR_YUV2BGR_UYVY = 108,
    //COLOR_YUV2RGB_VYUY = 109,
    //COLOR_YUV2BGR_VYUY = 110,
    COLOR_YUV2RGB_Y422 = COLOR_YUV2RGB_UYVY,
    COLOR_YUV2BGR_Y422 = COLOR_YUV2BGR_UYVY,
    COLOR_YUV2RGB_UYNV = COLOR_YUV2RGB_UYVY,
    COLOR_YUV2BGR_UYNV = COLOR_YUV2BGR_UYVY,

    COLOR_YUV2RGBA_UYVY = 111,
    COLOR_YUV2BGRA_UYVY = 112,
    //COLOR_YUV2RGBA_VYUY = 113,
    //COLOR_YUV2BGRA_VYUY = 114,
    COLOR_YUV2RGBA_Y422 = COLOR_YUV2RGBA_UYVY,
    COLOR_YUV2BGRA_Y422 = COLOR_YUV2BGRA_UYVY,
    COLOR_YUV2RGBA_UYNV = COLOR_YUV2RGBA_UYVY,
    COLOR_YUV2BGRA_UYNV = COLOR_YUV2BGRA_UYVY,

    COLOR_YUV2RGB_YUY2 = 115,
    COLOR_YUV2BGR_YUY2 = 116,
    COLOR_YUV2RGB_YVYU = 117,
    COLOR_YUV2BGR_YVYU = 118,
    COLOR_YUV2RGB_YUYV = COLOR_YUV2RGB_YUY2,
    COLOR_YUV2BGR_YUYV = COLOR_YUV2BGR_YUY2,
    COLOR_YUV2RGB_YUNV = COLOR_YUV2RGB_YUY2,
    COLOR_YUV2BGR_YUNV = COLOR_YUV2BGR_YUY2,

    COLOR_YUV2RGBA_YUY2 = 119,
    COLOR_YUV2BGRA_YUY2 = 120,
    COLOR_YUV2RGBA_YVYU = 121,
    COLOR_YUV2BGRA_YVYU = 122,
    COLOR_YUV2RGBA_YUYV = COLOR_YUV2RGBA_YUY2,
    COLOR_YUV2BGRA_YUYV = COLOR_YUV2BGRA_YUY2,
    COLOR_YUV2RGBA_YUNV = COLOR_YUV2RGBA_YUY2,
    COLOR_YUV2BGRA_YUNV = COLOR_YUV2BGRA_YUY2,

    COLOR_YUV2GRAY_UYVY = 123,
    COLOR_YUV2GRAY_YUY2 = 124,
    //CV_YUV2GRAY_VYUY    = CV_YUV2GRAY_UYVY,
    COLOR_YUV2GRAY_Y422 = COLOR_YUV2GRAY_UYVY,
    COLOR_YUV2GRAY_UYNV = COLOR_YUV2GRAY_UYVY,
    COLOR_YUV2GRAY_YVYU = COLOR_YUV2GRAY_YUY2,
    COLOR_YUV2GRAY_YUYV = COLOR_YUV2GRAY_YUY2,
    COLOR_YUV2GRAY_YUNV = COLOR_YUV2GRAY_YUY2,

    //! alpha premultiplication
    COLOR_RGBA2mRGBA    = 125,
    COLOR_mRGBA2RGBA    = 126,

    //! RGB to YUV 4:2:0 family
    COLOR_RGB2YUV_I420  = 127,
    COLOR_BGR2YUV_I420  = 128,
    COLOR_RGB2YUV_IYUV  = COLOR_RGB2YUV_I420,
    COLOR_BGR2YUV_IYUV  = COLOR_BGR2YUV_I420,

    COLOR_RGBA2YUV_I420 = 129,
    COLOR_BGRA2YUV_I420 = 130,
    COLOR_RGBA2YUV_IYUV = COLOR_RGBA2YUV_I420,
    COLOR_BGRA2YUV_IYUV = COLOR_BGRA2YUV_I420,
    COLOR_RGB2YUV_YV12  = 131,
    COLOR_BGR2YUV_YV12  = 132,
    COLOR_RGBA2YUV_YV12 = 133,
    COLOR_BGRA2YUV_YV12 = 134,

    //! Demosaicing
    COLOR_BayerBG2BGR = 46,
    COLOR_BayerGB2BGR = 47,
    COLOR_BayerRG2BGR = 48,
    COLOR_BayerGR2BGR = 49,

    COLOR_BayerBG2RGB = COLOR_BayerRG2BGR,
    COLOR_BayerGB2RGB = COLOR_BayerGR2BGR,
    COLOR_BayerRG2RGB = COLOR_BayerBG2BGR,
    COLOR_BayerGR2RGB = COLOR_BayerGB2BGR,

    COLOR_BayerBG2GRAY = 86,
    COLOR_BayerGB2GRAY = 87,
    COLOR_BayerRG2GRAY = 88,
    COLOR_BayerGR2GRAY = 89,

    //! Demosaicing using Variable Number of Gradients
    COLOR_BayerBG2BGR_VNG = 62,
    COLOR_BayerGB2BGR_VNG = 63,
    COLOR_BayerRG2BGR_VNG = 64,
    COLOR_BayerGR2BGR_VNG = 65,

    COLOR_BayerBG2RGB_VNG = COLOR_BayerRG2BGR_VNG,
    COLOR_BayerGB2RGB_VNG = COLOR_BayerGR2BGR_VNG,
    COLOR_BayerRG2RGB_VNG = COLOR_BayerBG2BGR_VNG,
    COLOR_BayerGR2RGB_VNG = COLOR_BayerGB2BGR_VNG,

    //! Edge-Aware Demosaicing
    COLOR_BayerBG2BGR_EA  = 135,
    COLOR_BayerGB2BGR_EA  = 136,
    COLOR_BayerRG2BGR_EA  = 137,
    COLOR_BayerGR2BGR_EA  = 138,

    COLOR_BayerBG2RGB_EA  = COLOR_BayerRG2BGR_EA,
    COLOR_BayerGB2RGB_EA  = COLOR_BayerGR2BGR_EA,
    COLOR_BayerRG2RGB_EA  = COLOR_BayerBG2BGR_EA,
    COLOR_BayerGR2RGB_EA  = COLOR_BayerGB2BGR_EA,

    COLOR_COLORCVT_MAX  = 139
};