OpenCV的颜色空间转换函数：
C++:
void cvtColor(InputArray src, OutputArray dst, int code, int dstCn=0 )参数dstCn原来一直沿用CV_BGR2GRAY, CV_RGB2GRAY, CV_GRAY2BGR, CV_GRAY2RGB等格式，但最新几个版本的OpenCV已改为COLOR_BGR2GRAY类似形式，今天才看源代码imgproc.hpp才发现，但官方文档还没修改，如下图，如果程序中使用较新的版本OpenCV，采用CV_BGR2GRAY可能会一直出错。
新的OpenCV中imgproc.hpp的定义如下：
enum { COLOR_BGR2BGRA =0, COLOR_RGB2RGBA =COLOR_BGR2BGRA, COLOR_BGRA2BGR =1, COLOR_RGBA2RGB =COLOR_BGRA2BGR, COLOR_BGR2RGBA =2, COLOR_RGB2BGRA =COLOR_BGR2RGBA, COLOR_RGBA2BGR =3, COLOR_BGRA2RGB =COLOR_RGBA2BGR, COLOR_BGR2RGB =4, COLOR_RGB2BGR =COLOR_BGR2RGB, COLOR_BGRA2RGBA =5, COLOR_RGBA2BGRA =COLOR_BGRA2RGBA, COLOR_BGR2GRAY =6, 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, COLOR_RGB2BGR565 =13, COLOR_BGR5652BGR =14, COLOR_BGR5652RGB =15, COLOR_BGRA2BGR565 =16, COLOR_RGBA2BGR565 =17, COLOR_BGR5652BGRA =18, COLOR_BGR5652RGBA =19, COLOR_GRAY2BGR565 =20, COLOR_BGR5652GRAY =21, COLOR_BGR2BGR555 =22, COLOR_RGB2BGR555 =23, COLOR_BGR5552BGR =24, COLOR_BGR5552RGB =25, COLOR_BGRA2BGR555 =26, COLOR_RGBA2BGR555 =27, COLOR_BGR5552BGRA =28, COLOR_BGR5552RGBA =29, COLOR_GRAY2BGR555 =30, COLOR_BGR5552GRAY =31, COLOR_BGR2XYZ =32, COLOR_RGB2XYZ =33, COLOR_XYZ2BGR =34, COLOR_XYZ2RGB =35, COLOR_BGR2YCrCb =36, COLOR_RGB2YCrCb =37, COLOR_YCrCb2BGR =38, COLOR_YCrCb2RGB =39, COLOR_BGR2HSV =40, COLOR_RGB2HSV =41, COLOR_BGR2Lab =44, COLOR_RGB2Lab =45, 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_BGR2Luv =50, COLOR_RGB2Luv =51, COLOR_BGR2HLS =52, COLOR_RGB2HLS =53, COLOR_HSV2BGR =54, COLOR_HSV2RGB =55, COLOR_Lab2BGR =56, COLOR_Lab2RGB =57, COLOR_Luv2BGR =58, COLOR_Luv2RGB =59, COLOR_HLS2BGR =60, COLOR_HLS2RGB =61, 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, 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, COLOR_RGB2YUV = 83, COLOR_YUV2BGR = 84, COLOR_YUV2RGB = 85, COLOR_BayerBG2GRAY = 86, COLOR_BayerGB2GRAY = 87, COLOR_BayerRG2GRAY = 88, COLOR_BayerGR2GRAY = 89, //YUV 4:2:0 formats family 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 formats family 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, //COLOR_YUV2GRAY_VYUY = COLOR_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, 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, COLOR_COLORCVT_MAX = 135 };