How to get value of specific pixel after converting to hsv?

Question

I have created a small program to detect red color by converting image to hsv. For detecting red color I am using the min range 170,160,160 and max range 180,255,255. So I got hsv image which shows red color in white. Now I want to know the value of that white pixel. I know the x,y coordinate.How would I get pixel value? I am using python and cv2.

Answer 1

So you already have x and y,

-> Just create ROI Mat with 1X1 size

-> Convert HSV colour space using CvtColor()

-> Access pixel value of above result

Mat image; //load image here
Mat HSV;
Mat RGB=image(Rect(x,y,1,1)); // use your x and y value

cvtColor(RGB, HSV,CV_BGR2HSV);
Vec3b hsv=HSV.at<Vec3b>(0,0);
int H=hsv.val[0]; //hue
int S=hsv.val[1]; //saturation
int V=hsv.val[2]; //value

You can refer below C++ code which will display RGB and HSV value for the pixel corresponding mouse position.

char window_name[30] = "HSV Segmentation";
Mat src;

static void onMouse( int event, int x, int y, int f, void* ){
 Mat image=src.clone();
 Vec3b rgb=image.at<Vec3b>(y,x);
 int B=rgb.val[0];
 int G=rgb.val[1];
 int R=rgb.val[2];

  Mat HSV;
  Mat RGB=image(Rect(x,y,1,1));
  cvtColor(RGB, HSV,CV_BGR2HSV);

    Vec3b hsv=HSV.at<Vec3b>(0,0);
    int H=hsv.val[0];
    int S=hsv.val[1];
    int V=hsv.val[2];

    char name[30];
    sprintf(name,"B=%d",B);
    putText(image,name, Point(150,40) , FONT_HERSHEY_SIMPLEX, .7, Scalar(0,255,0), 2,8,false );

    sprintf(name,"G=%d",G);
    putText(image,name, Point(150,80) , FONT_HERSHEY_SIMPLEX, .7, Scalar(0,255,0), 2,8,false );

    sprintf(name,"R=%d",R);
    putText(image,name, Point(150,120) , FONT_HERSHEY_SIMPLEX, .7, Scalar(0,255,0), 2,8,false );

    sprintf(name,"H=%d",H);
    putText(image,name, Point(25,40) , FONT_HERSHEY_SIMPLEX, .7, Scalar(0,255,0), 2,8,false );

    sprintf(name,"S=%d",S);
    putText(image,name, Point(25,80) , FONT_HERSHEY_SIMPLEX, .7, Scalar(0,255,0), 2,8,false );

    sprintf(name,"V=%d",V);
    putText(image,name, Point(25,120) , FONT_HERSHEY_SIMPLEX, .7, Scalar(0,255,0), 2,8,false );

    sprintf(name,"X=%d",x);
    putText(image,name, Point(25,300) , FONT_HERSHEY_SIMPLEX, .7, Scalar(0,0,255), 2,8,false );

    sprintf(name,"Y=%d",y);
    putText(image,name, Point(25,340) , FONT_HERSHEY_SIMPLEX, .7, Scalar(0,0,255), 2,8,false );

 //imwrite("hsv.jpg",image);
 imshow( window_name, image );
}



int main(){
 src = imread("bgr.png",1);
 imshow(window_name,src);
 setMouseCallback( window_name, onMouse, 0 );
 waitKey();  
 }

Answer 2

@user3352710 @Pe Dro Hum it's really easy to do that on python. Here is the simple code for it.

def coords_mouse_disp(event,x,y,flags,param):
    if event == cv2.EVENT_LBUTTONDBLCLK: #left mouse double click 
         print("Orginal BGR:",img[x,y])
         print("HSV values:", HSV[x,y])

path = "your_image_path.png"
while True:
    img = cv2.imread(path)
    #img = cv2.resize(img, None, fx=0.5, fy=0.5)
    HSV = cv2.cvtColor(img,cv2.COLOR_BGR2HSV)

    cv2.imshow("Original",img)
    cv2.imshow("HSV", HSV)
    #left mouse click event
    cv2.setMouseCallback("HSV", coords_mouse_disp)
    cv2.setMouseCallback("Original", coords_mouse_disp)

    if cv2.waitKey(1) &0xFF == ord("q"):
        cv2.destroyAllWindows()
        break