Simple color detection by Hue - Hue(HSV)값으로 특정색 검출하기

Hue is the color portion of the model, expressed as a number from 0 to 360 degrees:

Red: falls between 0 and 60 degrees.

Yellow: falls between 61 and 120 degrees.

Green: falls between 121-180 degrees.

Cyan: falls between 181-240 degrees.

Blue: falls between 241-300 degrees.

Magenta: falls between 301-360 degrees.

For HSV, OpenCV Hue range is [0,179], Saturation range is [0,255] and Value range is [0,255]. Different software uses different scales. So if you are comparing OpenCV values with them, you need to normalize these ranges.

HSV(Hue)를 이용하면 RGB를 이용하는 것 보다 간단히 특정색을 검출할 수 있다. OpenCV의 Hue값은 0~179 이다.

#include <opencv2/opencv.hpp>
 
using namespace std;
using namespace cv;
 
int lowerHue = 40, upperHue = 80;    // Green
Mat src, src_hsv, mask, dst;
 
void OnHueChenaged(int pos, void* userdata)
{
    Scalar lowerb(lowerHue, 100, 0);
    Scalar upperb(upperHue, 255, 255);
 
    inRange(src_hsv, lowerb, upperb, mask);
    // Checks if array elements lie between the elements of two other arrays.
 
    dst.setTo(0);    // 매번 초기화 해 주지 않으면 이전에 선택한 색과 겹친다.
    src.copyTo(dst, mask);
    // The method copies the matrix data to another matrix. Before copying the data, the method invokes: m.create(this->size(), this->type());
    // so that the destination matrix is reallocated if needed.While m.copyTo(m); works flawlessly, the function does not handle the case of a
    // partial overlap between the sourceand the destination matrices. When the operation mask is specified, if the Mat::create call shown above
    // reallocates the matrix, the newly allocated matrix is initialized with all zeros before copying the data.
 
    imshow("mask", mask);
    imshow("dst", dst);
}
 
int main(int argc, char** argv)
{
    src = imread("candies.jpg", IMREAD_COLOR);
    if (src.empty()) {
        cerr << "Image load failed." << endl;
        
        return -1;
    }
 
    imshow("src", src);
 
    cvtColor(src, src_hsv, COLOR_BGR2HSV);
 
    namedWindow("mask");
    createTrackbar("Lower Hue", "mask", &lowerHue, 179, OnHueChenaged);
    createTrackbar("Upper Hue", "mask", &upperHue, 179, OnHueChenaged);
    OnHueChenaged(NULL, NULL);
 
    waitKey(0);
    
    return 0;
}

Original candy image.

Mask for green color.

Green candies detected.