OpenCV-3.4.3图像通道处理

• 图像通道处理

图像读取和处理都是按BGR通道顺序进行的

 #include <iostream>
 #include <opencv2/opencv.hpp>
 #include "opencv2/highgui/highgui.hpp"
 #include "opencv2/imgproc/imgproc.hpp"

 int main(int argc, char **argv) {
     cv::Mat src = cv::imread("/home/cv/Downloads/images/P1180141.JPG", );
     cv::resize(src, src, cv::Size(src.cols / , src.rows / ), cv::INTER_CUBIC);
     cv::imshow("original_after_resize", src);

     // blue channel
     cv::Mat mytemp1(src.rows, src.cols, CV_8UC3, cv::Scalar(, , ));
     cv::imshow("temp test", mytemp1);
     // green channel
     cv::Mat mytemp2(src.rows, src.cols, CV_8UC3, cv::Scalar(, , ));
     cv::imshow("temp test", mytemp2);
     // red channel
     cv::Mat mytemp3(src.rows, src.cols, CV_8UC3, cv::Scalar(, , ));
     cv::imshow("temp test", mytemp3);
     cv::waitKey();
     return ;
 }

或者使用mixChannels函数

 #include <opencv2/opencv.hpp>
 #include "opencv2/highgui/highgui.hpp"
 #include "opencv2/imgproc/imgproc.hpp"

 int main(int argc, char **argv) {
     cv::Mat src = cv::imread("/home/cv/Downloads/images/P1180141.JPG", );
     cv::resize(src, src, cv::Size(src.cols / , src.rows / ), cv::INTER_CUBIC);
     for (int i = ; i < ; i++) {
         cv::Mat temp_bgr(src.rows, src.cols, CV_8UC3, cv::Scalar(, , ));
         cv::Mat temp(src.rows, src.cols, CV_8UC1);
         cv::Mat out[] = {temp_bgr};
         int from_to[] = {i, i};
         cv::mixChannels(&src, , out, , from_to, );
         cv::imshow("single channel", temp_bgr);
         cv::waitKey();
     }

     return ;
 }

转换到HSV颜色空间查看效果

 #include <iostream>
 #include <opencv2/opencv.hpp>
 #include "opencv2/highgui/highgui.hpp"
 #include "opencv2/imgproc/imgproc.hpp"

 int main(int argc, char **argv) {
     cv::Mat src = cv::imread("/home/cv/Downloads/images/P1180141.JPG", );
     cv::resize(src, src, cv::Size(src.cols / , src.rows / ), cv::INTER_CUBIC);
     cv::imshow("original_after_resize", src);

     cv::Mat img_hsv;
     cv::cvtColor(src, img_hsv, CV_BGR2HSV);
     cv::Mat dst;
     dst.create(img_hsv.size(), img_hsv.depth());

     int ch[] = {, };
     int ch1[] = {, };
     int ch2[] = {, };

     // Hue 色调通道
     cv::mixChannels(&img_hsv, , &dst, , ch, );
     cv::imshow("hsv-h", dst);
     // Saturation 饱和度通道
     cv::mixChannels(&img_hsv, , &dst, , ch1, );
     cv::imshow("hsv-s", dst);
     // Lightness/Value 亮度/像素值通道
     cv::mixChannels(&img_hsv, , &dst, , ch2, );
     cv::imshow("hsv-v", dst);
     cv::waitKey();

     return ;
 }

转换到YUV空间或YCrCb空间查看效果

 #include <iostream>
 #include <vector>
 #include <opencv2/opencv.hpp>
 #include "opencv2/highgui/highgui.hpp"
 #include "opencv2/imgproc/imgproc.hpp"

 int main(int argc, char **argv) {
     cv::Mat src = cv::imread("/home/cv/Downloads/images/P1180141.JPG", );
     cv::resize(src, src, cv::Size(src.cols / , src.rows / ), cv::INTER_CUBIC);
     cv::imshow("original_after_resize", src);

     // YUV color space
     cv::Mat img_yuv;
     cv::cvtColor(src, img_yuv, CV_BGR2YUV);
     cv::Mat dst;
     dst.create(img_yuv.size(), img_yuv.depth());

     // Luminance, 明亮度，灰度值
     int ch[] = {, };
     cv::mixChannels(&img_yuv, , &dst, , ch, );
     cv::imshow("yuv-y", dst);
     // Chrominance, 色彩及饱和度，指定像素的颜色
     int ch1[] = {, };
     cv::mixChannels(&img_yuv, , &dst, , ch1, );
     cv::imshow("yuv-u", dst);
     int ch2[] = {, };
     cv::mixChannels(&img_yuv, , &dst, , ch2, );
     cv::imshow("yuv-v", dst);

     // YCrCb color space
     cv::Mat ycrb;
     cv::cvtColor(src, ycrb, CV_BGR2YCrCb);
     std::vector<cv::Mat> mv;
     cv::split(ycrb, (std::vector<cv::Mat>&) mv);

     // Y channel
     cv::Mat chy(src.rows, src.cols, CV_8UC1);
     chy = mv[].clone();
     cv::imshow("Y", chy);
     // Cr and Cb channel
     // Cr反映RGB输入信号红色部分与RGB信号亮度值之间的差异
     // Cb反应RGB输入信号蓝色部分与RGB信号亮度值之间的差异
     cv::Mat chu(src.rows, src.cols, CV_8UC1);
     chu = mv[].clone();
     cv::imshow("Cr", chu);
     cv::Mat chv(src.rows, src.cols, CV_8UC1);
     chv = mv[].clone();
     cv::imshow("Cb", chv);
     cv::waitKey();

     return ;
 }

•  cv::Mat 类型的成员函数 depth 

查看官方文档

inline
int Mat::depth() const
{
    return CV_MAT_DEPTH(flags);
}

其中的 CV_MAT_DEPTH 定义如下

#define CV_MAT_DEPTH(flags)     ((flags) & CV_MAT_DEPTH_MASK)

这里的 CV_MAT_DEPTH_MASK 定义如下

#define CV_MAT_DEPTH_MASK       (CV_DEPTH_MAX - 1)

宏定义中的 CV_DEPTH_MAX 定义如下

#define CV_CN_SHIFT 3
#define CV_DEPTH_MAX (1 << CV_CN_SHIFT)

Mat::type
Returns the type of a matrix element.

C++: int Mat::type() const
The method returns a matrix element type. This is an identifier compatible with the CvMat type system, like CV_16SC3 or 16-bit signed 3-channel array, and so on.

表格来源(OpenCV学习十七：OpenCV中Mat的type)

出处暂不可考

Mat::depth
Returns the depth of a matrix element.

C++: int Mat::depth() const
The method returns the identifier of the matrix element depth (the type of each individual channel). For example, for a 16-bit signed element array, the method returns CV_16S . A complete list of matrix types contains the following values:

#define CV_8U 0
#define CV_8S 1
#define CV_16U 2
#define CV_16S 3
#define CV_32S 4
#define CV_32F 5
#define CV_64F 6
#define CV_USRTYPE1 7

CV_8U - -bit unsigned integers ( .. )
CV_8S - -bit signed integers ( -.. )
CV_16U - -bit unsigned integers ( .. )
CV_16S - -bit signed integers ( -.. )
CV_32S - -bit signed integers ( -.. )
CV_32F - -bit floating-point numbers ( -FLT_MAX..FLT_MAX, INF, NAN )
CV_64F - -bit floating-point numbers ( -DBL_MAX..DBL_MAX, INF, NAN )

转换函数

void cv::transform (InputArray src,
    OutputArray dst,
    InputArray m
)

The function cv::transform performs the matrix transformation of every element of the array src and stores the results in dst :