12.1、常見的色彩空間

12.1.1、RGB色彩空間

RGB色彩空間源于使用陰極射線管（CRT） 的彩色電視。 RGB模型使用加性色彩混合 以獲知需要發(fā)出什么樣的光來(lái)產(chǎn)生給定的色彩。 具體色彩的值用三個(gè)數(shù)值的向量來(lái)表 示， 這三個(gè)數(shù)值分別代表三種基色： Red、 Green、 Blue的亮度。 假設(shè)每種基色的數(shù)值量 化成m=2^n個(gè)數(shù)， 如同8位灰度圖像一樣， 將灰度量化成28 =256個(gè)數(shù)。 RGB圖像的紅、 綠、 藍(lán)三個(gè)通道的圖像都是一幅8位圖， 因此顏色的總數(shù)為256*3 =16777216， 如（0， 0， 0） 代表黑色，（255， 255， 255）代表白色。

12.1.2、HSV色彩空間

HSV——色調(diào)（Hue） 、 飽和度（Saturation） 、 亮度值（Value） ， 又稱HSB——色調(diào)（Hue） 、 飽和度（Saturation） 、亮度（Brightness） ，HSV將亮度信息從彩色中分解出來(lái)， 而色調(diào)和飽和度與人類感知是相對(duì)應(yīng)的， 因而使得該模型在開發(fā)圖像算法中非常有用。 如果將對(duì)比度增強(qiáng)算法用在RGB的每個(gè)分量上， 那么人類對(duì)該圖像的色彩感知就變得不夠理想了； 而如果僅對(duì)HSV的亮度分量進(jìn)行增強(qiáng)，讓彩色信息不受影響， 那么效果就會(huì)或多或少地與期望相近。

12.1.3、HLS色彩空間

HLS色彩空間主要使用三個(gè)數(shù)值來(lái)描述色彩，分別是H（Hue， 色調(diào)） 、 L（Lightness/Luminance， 光亮度/明度） 、 S（Saturation， 飽和度） 。 HLS色彩空間也稱 作HSI——Hue（色調(diào)） 、 Saturation（飽和度） 、 Intensity（亮度） 。 與HSV類似， HLS只是用“光亮度”替換了“亮度”， 差別在于一種純色的亮度等于白 色的亮度， 而一種純色的光亮度等于中度灰的光亮度。 色調(diào)用來(lái)描述一個(gè)純色彩的基本屬性， 即在日常生活中所使用的基本色彩名稱， 比如藍(lán)色、 紅色等。 亮度是用來(lái)描述明亮程度的， 通過百分比的方式來(lái)表示， 以[0， 1]范圍進(jìn)行量化。 通過亮度的大小來(lái)衡量有多少光線從物體表面反射出來(lái)， 是幫助眼睛去感知色彩的重要屬性。 顯然， 當(dāng)一個(gè)具有色彩的物體處于較暗或者較亮的地方時(shí)， 眼睛通常無(wú)法正確地分 辨出物體表面原本的色彩。 飽和度是用來(lái)描述純色彩所添加的白光的程度的， 即色彩的純度。 飽和度通過百分 比的方式來(lái)表示， 以[0， 1]范圍來(lái)量化。 飽和度的數(shù)值越高， 則表示色彩的純度越高； 反 之， 色彩的純度越低， 比如紅色， 會(huì)有深紅、 淺紅之分。

色彩空間的轉(zhuǎn)換接口

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

code如下

/** Constants for color conversion */
enum
{
CV_BGR2BGRA    =0,
CV_RGB2RGBA    =CV_BGR2BGRA,
CV_BGRA2BGR    =1,
CV_RGBA2RGB    =CV_BGRA2BGR,

CV_BGR2RGBA    =2,
CV_RGB2BGRA    =CV_BGR2RGBA,

CV_RGBA2BGR    =3,
CV_BGRA2RGB    =CV_RGBA2BGR,

CV_BGR2RGB     =4,
CV_RGB2BGR     =CV_BGR2RGB,

CV_BGRA2RGBA   =5,
CV_RGBA2BGRA   =CV_BGRA2RGBA,

CV_BGR2GRAY    =6,
CV_RGB2GRAY    =7,
CV_GRAY2BGR    =8,
CV_GRAY2RGB    =CV_GRAY2BGR,
CV_GRAY2BGRA   =9,
CV_GRAY2RGBA   =CV_GRAY2BGRA,
CV_BGRA2GRAY   =10,
CV_RGBA2GRAY   =11,

CV_BGR2BGR565  =12,
CV_RGB2BGR565  =13,
CV_BGR5652BGR  =14,
CV_BGR5652RGB  =15,
CV_BGRA2BGR565 =16,
CV_RGBA2BGR565 =17,
CV_BGR5652BGRA =18,
CV_BGR5652RGBA =19,

CV_GRAY2BGR565 =20,
CV_BGR5652GRAY =21,

CV_BGR2BGR555  =22,
CV_RGB2BGR555  =23,
CV_BGR5552BGR  =24,
CV_BGR5552RGB  =25,
CV_BGRA2BGR555 =26,
CV_RGBA2BGR555 =27,
CV_BGR5552BGRA =28,
CV_BGR5552RGBA =29,

CV_GRAY2BGR555 =30,
CV_BGR5552GRAY =31,

CV_BGR2XYZ     =32,
CV_RGB2XYZ     =33,
CV_XYZ2BGR     =34,
CV_XYZ2RGB     =35,

CV_BGR2YCrCb   =36,
CV_RGB2YCrCb   =37,
CV_YCrCb2BGR   =38,
CV_YCrCb2RGB   =39,

CV_BGR2HSV     =40,
CV_RGB2HSV     =41,

CV_BGR2Lab     =44,
CV_RGB2Lab     =45,

CV_BayerBG2BGR =46,
CV_BayerGB2BGR =47,
CV_BayerRG2BGR =48,
CV_BayerGR2BGR =49,

CV_BayerBG2RGB =CV_BayerRG2BGR,
CV_BayerGB2RGB =CV_BayerGR2BGR,
CV_BayerRG2RGB =CV_BayerBG2BGR,
CV_BayerGR2RGB =CV_BayerGB2BGR,

CV_BGR2Luv     =50,
CV_RGB2Luv     =51,
CV_BGR2HLS     =52,
CV_RGB2HLS     =53,

CV_HSV2BGR     =54,
CV_HSV2RGB     =55,

CV_Lab2BGR     =56,
CV_Lab2RGB     =57,
CV_Luv2BGR     =58,
CV_Luv2RGB     =59,
CV_HLS2BGR     =60,
CV_HLS2RGB     =61,

CV_BayerBG2BGR_VNG =62,
CV_BayerGB2BGR_VNG =63,
CV_BayerRG2BGR_VNG =64,
CV_BayerGR2BGR_VNG =65,

CV_BayerBG2RGB_VNG =CV_BayerRG2BGR_VNG,
CV_BayerGB2RGB_VNG =CV_BayerGR2BGR_VNG,
CV_BayerRG2RGB_VNG =CV_BayerBG2BGR_VNG,
CV_BayerGR2RGB_VNG =CV_BayerGB2BGR_VNG,

CV_BGR2HSV_FULL = 66,
CV_RGB2HSV_FULL = 67,
CV_BGR2HLS_FULL = 68,
CV_RGB2HLS_FULL = 69,

CV_HSV2BGR_FULL = 70,
CV_HSV2RGB_FULL = 71,
CV_HLS2BGR_FULL = 72,
CV_HLS2RGB_FULL = 73,

CV_LBGR2Lab     = 74,
CV_LRGB2Lab     = 75,
CV_LBGR2Luv     = 76,
CV_LRGB2Luv     = 77,

CV_Lab2LBGR     = 78,
CV_Lab2LRGB     = 79,
CV_Luv2LBGR     = 80,
CV_Luv2LRGB     = 81,

CV_BGR2YUV      = 82,
CV_RGB2YUV      = 83,
CV_YUV2BGR      = 84,
CV_YUV2RGB      = 85,

CV_BayerBG2GRAY = 86,
CV_BayerGB2GRAY = 87,
CV_BayerRG2GRAY = 88,
CV_BayerGR2GRAY = 89,

//YUV 4:2:0 formats family
CV_YUV2RGB_NV12 = 90,
CV_YUV2BGR_NV12 = 91,
CV_YUV2RGB_NV21 = 92,
CV_YUV2BGR_NV21 = 93,
CV_YUV420sp2RGB = CV_YUV2RGB_NV21,
CV_YUV420sp2BGR = CV_YUV2BGR_NV21,

CV_YUV2RGBA_NV12 = 94,
CV_YUV2BGRA_NV12 = 95,
CV_YUV2RGBA_NV21 = 96,
CV_YUV2BGRA_NV21 = 97,
CV_YUV420sp2RGBA = CV_YUV2RGBA_NV21,
CV_YUV420sp2BGRA = CV_YUV2BGRA_NV21,

CV_YUV2RGB_YV12 = 98,
CV_YUV2BGR_YV12 = 99,
CV_YUV2RGB_IYUV = 100,
CV_YUV2BGR_IYUV = 101,
CV_YUV2RGB_I420 = CV_YUV2RGB_IYUV,
CV_YUV2BGR_I420 = CV_YUV2BGR_IYUV,
CV_YUV420p2RGB = CV_YUV2RGB_YV12,
CV_YUV420p2BGR = CV_YUV2BGR_YV12,

CV_YUV2RGBA_YV12 = 102,
CV_YUV2BGRA_YV12 = 103,
CV_YUV2RGBA_IYUV = 104,
CV_YUV2BGRA_IYUV = 105,
CV_YUV2RGBA_I420 = CV_YUV2RGBA_IYUV,
CV_YUV2BGRA_I420 = CV_YUV2BGRA_IYUV,
CV_YUV420p2RGBA = CV_YUV2RGBA_YV12,
CV_YUV420p2BGRA = CV_YUV2BGRA_YV12,

CV_YUV2GRAY_420 = 106,
CV_YUV2GRAY_NV21 = CV_YUV2GRAY_420,
CV_YUV2GRAY_NV12 = CV_YUV2GRAY_420,
CV_YUV2GRAY_YV12 = CV_YUV2GRAY_420,
CV_YUV2GRAY_IYUV = CV_YUV2GRAY_420,
CV_YUV2GRAY_I420 = CV_YUV2GRAY_420,
CV_YUV420sp2GRAY = CV_YUV2GRAY_420,
CV_YUV420p2GRAY = CV_YUV2GRAY_420,

//YUV 4:2:2 formats family
CV_YUV2RGB_UYVY = 107,
CV_YUV2BGR_UYVY = 108,
//CV_YUV2RGB_VYUY = 109,
//CV_YUV2BGR_VYUY = 110,
CV_YUV2RGB_Y422 = CV_YUV2RGB_UYVY,
CV_YUV2BGR_Y422 = CV_YUV2BGR_UYVY,
CV_YUV2RGB_UYNV = CV_YUV2RGB_UYVY,
CV_YUV2BGR_UYNV = CV_YUV2BGR_UYVY,

CV_YUV2RGBA_UYVY = 111,
CV_YUV2BGRA_UYVY = 112,
//CV_YUV2RGBA_VYUY = 113,
//CV_YUV2BGRA_VYUY = 114,
CV_YUV2RGBA_Y422 = CV_YUV2RGBA_UYVY,
CV_YUV2BGRA_Y422 = CV_YUV2BGRA_UYVY,
CV_YUV2RGBA_UYNV = CV_YUV2RGBA_UYVY,
CV_YUV2BGRA_UYNV = CV_YUV2BGRA_UYVY,

CV_YUV2RGB_YUY2 = 115,
CV_YUV2BGR_YUY2 = 116,
CV_YUV2RGB_YVYU = 117,
CV_YUV2BGR_YVYU = 118,
CV_YUV2RGB_YUYV = CV_YUV2RGB_YUY2,
CV_YUV2BGR_YUYV = CV_YUV2BGR_YUY2,
CV_YUV2RGB_YUNV = CV_YUV2RGB_YUY2,
CV_YUV2BGR_YUNV = CV_YUV2BGR_YUY2,

CV_YUV2RGBA_YUY2 = 119,
CV_YUV2BGRA_YUY2 = 120,
CV_YUV2RGBA_YVYU = 121,
CV_YUV2BGRA_YVYU = 122,
CV_YUV2RGBA_YUYV = CV_YUV2RGBA_YUY2,
CV_YUV2BGRA_YUYV = CV_YUV2BGRA_YUY2,
CV_YUV2RGBA_YUNV = CV_YUV2RGBA_YUY2,
CV_YUV2BGRA_YUNV = CV_YUV2BGRA_YUY2,

CV_YUV2GRAY_UYVY = 123,
CV_YUV2GRAY_YUY2 = 124,
//CV_YUV2GRAY_VYUY = CV_YUV2GRAY_UYVY,
CV_YUV2GRAY_Y422 = CV_YUV2GRAY_UYVY,
CV_YUV2GRAY_UYNV = CV_YUV2GRAY_UYVY,
CV_YUV2GRAY_YVYU = CV_YUV2GRAY_YUY2,
CV_YUV2GRAY_YUYV = CV_YUV2GRAY_YUY2,
CV_YUV2GRAY_YUNV = CV_YUV2GRAY_YUY2,

// alpha premultiplication
CV_RGBA2mRGBA = 125,
CV_mRGBA2RGBA = 126,

CV_RGB2YUV_I420 = 127,
CV_BGR2YUV_I420 = 128,
CV_RGB2YUV_IYUV = CV_RGB2YUV_I420,
CV_BGR2YUV_IYUV = CV_BGR2YUV_I420,

CV_RGBA2YUV_I420 = 129,
CV_BGRA2YUV_I420 = 130,
CV_RGBA2YUV_IYUV = CV_RGBA2YUV_I420,
CV_BGRA2YUV_IYUV = CV_BGRA2YUV_I420,
CV_RGB2YUV_YV12  = 131,
CV_BGR2YUV_YV12  = 132,
CV_RGBA2YUV_YV12 = 133,
CV_BGRA2YUV_YV12 = 134,

// Edge-Aware Demosaicing
CV_BayerBG2BGR_EA = 135,
CV_BayerGB2BGR_EA = 136,
CV_BayerRG2BGR_EA = 137,
CV_BayerGR2BGR_EA = 138,

CV_BayerBG2RGB_EA = CV_BayerRG2BGR_EA,
CV_BayerGB2RGB_EA = CV_BayerGR2BGR_EA,
CV_BayerRG2RGB_EA = CV_BayerBG2BGR_EA,
CV_BayerGR2RGB_EA = CV_BayerGB2BGR_EA,

CV_BayerBG2BGRA =139,
CV_BayerGB2BGRA =140,
CV_BayerRG2BGRA =141,
CV_BayerGR2BGRA =142,

CV_BayerBG2RGBA =CV_BayerRG2BGRA,
CV_BayerGB2RGBA =CV_BayerGR2BGRA,
CV_BayerRG2RGBA =CV_BayerBG2BGRA,
CV_BayerGR2RGBA =CV_BayerGB2BGRA,

CV_COLORCVT_MAX  = 143
};      

12.2調(diào)整彩色圖像的飽和度和亮度

因?yàn)樵贖LS或HSV色彩空間中都將飽和度和亮度單獨(dú)分離出來(lái)， 所以首先將RGB圖像轉(zhuǎn)換為HLS或HSV圖像， 然后調(diào)整飽和度和亮度分量， 最后將調(diào)整后的HLS或者HSV圖像轉(zhuǎn)換為RGB圖像。

算法步驟：

• 第一步：將RGB圖像值歸一化到[0，1]；
• 第二步：使用函數(shù)cvtColor進(jìn)行色彩空間的轉(zhuǎn)換；
• 第三步：根據(jù)處理灰度圖像對(duì)比度增強(qiáng)的伽馬變換或者線性變換調(diào)整飽和度和亮度分量；
• 第四步：再轉(zhuǎn)換到RGB色彩空間。