CvtColor
色彩空间转换
void cvCvtColor( const CvArr* src, CvArr* dst, int code );
src
输入的 8-bit , 16-bit 或 32-bit 单倍精度浮点数影像.
dst
输出的 8-bit , 16-bit 或 32-bit 单倍精度浮点数影像.
code
色彩空间转换,通过定义 CV_2 常数 (见下面).
函数 cvCvtColor 将输入图像从一个色彩空间转换为另外一个色彩空间。函数忽略 IplImage 头中定义的 colorModel 和 channelSeq 域,所以输入图像的色彩空间应该正确指定 (包括通道的顺序,对RGB空间而言,BGR 意味着布局为 B0 G0 R0 B1 G1 R1 ... 层叠的 24-位格式,而 RGB 意味着布局为 R0 G0 B0 R1 G1 B1 ... 层叠的24-位格式. 函数做如下变换:
RGB 空间内部的变换,如增加/删除 alpha 通道,反相通道顺序,到16位 RGB彩色或者15位RGB彩色的正逆转换(Rx5:Gx6:Rx5),以及到灰度图像的正逆转换,使用:
RGB[A]->Gray: Y=0.212671*R + 0.715160*G + 0.072169*B + 0*A
Gray->RGB[A]: R=Y G=Y B=Y A=0
所有可能的图像色彩空间的相互变换公式列举如下:
RGB<=>XYZ (CV_BGR2XYZ, CV_RGB2XYZ, CV_XYZ2BGR, CV_XYZ2RGB):
|X| |0.412411 0.357585 0.180454| |R|
|Y| = |0.212649 0.715169 0.072182|*|G|
|Z| |0.019332 0.119195 0.950390| |B|
|R| | 3.240479 -1.53715 -0.498535| |X|
|G| = |-0.969256 1.875991 0.041556|*|Y|
|B| | 0.055648 -0.204043 1.057311| |Z|
RGB<=>YCrCb (CV_BGR2YCrCb, CV_RGB2YCrCb, CV_YCrCb2BGR, CV_YCrCb2RGB)
Y=0.299*R + 0.587*G + 0.114*B
Cr=(R-Y)*0.713 + 128
Cb=(B-Y)*0.564 + 128
R=Y + 1.403*(Cr - 128)
G=Y - 0.344*(Cr - 128) - 0.714*(Cb - 128)
B=Y + 1.773*(Cb - 128)
RGB=>HSV (CV_BGR2HSV,CV_RGB2HSV)
V=max(R,G,B)
S=(V-min(R,G,B))*255/V if V!=0, 0 otherwise
(G - B)*60/S, if V=R
H= 180+(B - R)*60/S, if V=G
240+(R - G)*60/S, if V=B
if H<0 then H=H+360
使用上面从 0° 到 360° 变化的公式计算色调(hue)值,确保它们被 2 除后能适用于8位。
RGB=>Lab (CV_BGR2Lab, CV_RGB2Lab)
|X| |0.433910 0.376220 0.189860| |R/255|
|Y| = |0.212649 0.715169 0.072182|*|G/255|
|Z| |0.017756 0.109478 0.872915| |B/255|
L = 116*Y1/3 for Y>0.008856
L = 903.3*Y for Y<=0.008856
a = 500*(f(X)-f(Y))
b = 200*(f(Y)-f(Z))
where f(t)=t1/3 for t>0.008856
f(t)=7.787*t+16/116 for t<=0.008856
上面的公式可以参考 http://www.cica.indiana.edu/cica/faq/color_spaces/color.spaces.html
Bayer=>RGB (CV_BayerBG2BGR, CV_BayerGB2BGR, CV_BayerRG2BGR, CV_BayerGR2BGR, CV_BayerBG2RGB, CV_BayerRG2BGR, CV_BayerGB2RGB, CV_BayerGR2BGR, CV_BayerRG2RGB, CV_BayerBG2BGR, CV_BayerGR2RGB, CV_BayerGB2BGR)
Bayer 模式被广泛应用于 CCD 和 CMOS 摄像头. 它允许从一个单独平面中得到彩色图像,该平面中的 R/G/B 象素点被安排如下:
R G R G R
G B G B G
R G R G R
G B G B G
R G R G R
G B G B G
对像素输出的RGB份量由该像素的1、2或者4邻域中具有相同颜色的点插值得到。以上的模式可以通过向左或者向上平移一个像素点来作一些修改。转换 常量CV_BayerC1C22{RGB|RGB}中的两个字母C1和C2表示特定的模式类型:颜色份量分别来自于第二行,第二和第三列。比如说,上述的 模式具有很流行的"BG"类型。
【以上引自http://www.opencv.org.cn/index.php/Cv%E5%9B%BE%E5%83%8F%E5%A4%84%E7%90%86#CvtColor
】
【附:opencv库中附带源码】
/* Constants for color conversion */
#define CV_BGR2BGRA 0
#define CV_RGB2RGBA CV_BGR2BGRA
#define CV_BGRA2BGR 1
#define CV_RGBA2RGB CV_BGRA2BGR
#define CV_BGR2RGBA 2
#define CV_RGB2BGRA CV_BGR2RGBA
#define CV_RGBA2BGR 3
#define CV_BGRA2RGB CV_RGBA2BGR
#define CV_BGR2RGB 4
#define CV_RGB2BGR CV_BGR2RGB
#define CV_BGRA2RGBA 5
#define CV_RGBA2BGRA CV_BGRA2RGBA
#define CV_BGR2GRAY 6
#define CV_RGB2GRAY 7
#define CV_GRAY2BGR 8
#define CV_GRAY2RGB CV_GRAY2BGR
#define CV_GRAY2BGRA 9
#define CV_GRAY2RGBA CV_GRAY2BGRA
#define CV_BGRA2GRAY 10
#define CV_RGBA2GRAY 11
#define CV_BGR2BGR565 12
#define CV_RGB2BGR565 13
#define CV_BGR5652BGR 14
#define CV_BGR5652RGB 15
#define CV_BGRA2BGR565 16
#define CV_RGBA2BGR565 17
#define CV_BGR5652BGRA 18
#define CV_BGR5652RGBA 19
#define CV_GRAY2BGR565 20
#define CV_BGR5652GRAY 21
#define CV_BGR2BGR555 22
#define CV_RGB2BGR555 23
#define CV_BGR5552BGR 24
#define CV_BGR5552RGB 25
#define CV_BGRA2BGR555 26
#define CV_RGBA2BGR555 27
#define CV_BGR5552BGRA 28
#define CV_BGR5552RGBA 29
#define CV_GRAY2BGR555 30
#define CV_BGR5552GRAY 31
#define CV_BGR2XYZ 32
#define CV_RGB2XYZ 33
#define CV_XYZ2BGR 34
#define CV_XYZ2RGB 35
#define CV_BGR2YCrCb 36
#define CV_RGB2YCrCb 37
#define CV_YCrCb2BGR 38
#define CV_YCrCb2RGB 39
#define CV_BGR2HSV 40
#define CV_RGB2HSV 41
#define CV_BGR2Lab 44
#define CV_RGB2Lab 45
#define CV_BayerBG2BGR 46
#define CV_BayerGB2BGR 47
#define CV_BayerRG2BGR 48
#define CV_BayerGR2BGR 49
#define CV_BayerBG2RGB CV_BayerRG2BGR
#define CV_BayerGB2RGB CV_BayerGR2BGR
#define CV_BayerRG2RGB CV_BayerBG2BGR
#define CV_BayerGR2RGB CV_BayerGB2BGR
#define CV_BGR2Luv 50
#define CV_RGB2Luv 51
#define CV_BGR2HLS 52
#define CV_RGB2HLS 53
#define CV_HSV2BGR 54
#define CV_HSV2RGB 55
#define CV_Lab2BGR 56
#define CV_Lab2RGB 57
#define CV_Luv2BGR 58
#define CV_Luv2RGB 59
#define CV_HLS2BGR 60
#define CV_HLS2RGB 61
#define CV_COLORCVT_MAX 100