Merge pull request #23108 from crackwitz:issue-23107

Usage of imread(): magic number 0, unchecked result

* docs: rewrite 0/1 to IMREAD_GRAYSCALE/IMREAD_COLOR in imread()

* samples, apps: rewrite 0/1 to IMREAD_GRAYSCALE/IMREAD_COLOR in imread()

* tests: rewrite 0/1 to IMREAD_GRAYSCALE/IMREAD_COLOR in imread()

* doc/py_tutorials: check imread() result

samples/cpp/tutorial_code/snippets/imgproc_HoughLinesCircles.cpp

@@ -8,7 +8,7 @@ using namespace std;
 int main(int argc, char** argv)
 {
     Mat img, gray;
-    if( argc != 2 || !(img=imread(argv[1], 1)).data)
+    if( argc != 2 || !(img=imread(argv[1], IMREAD_COLOR)).data)
         return -1;
     cvtColor(img, gray, COLOR_BGR2GRAY);
     // smooth it, otherwise a lot of false circles may be detected

samples/cpp/tutorial_code/snippets/imgproc_HoughLinesP.cpp

@@ -7,7 +7,7 @@ using namespace std;
 int main(int argc, char** argv)
 {
     Mat src, dst, color_dst;
-    if( argc != 2 || !(src=imread(argv[1], 0)).data)
+    if( argc != 2 || !(src=imread(argv[1], IMREAD_GRAYSCALE)).data)
         return -1;
 
     Canny( src, dst, 50, 200, 3 );

samples/cpp/tutorial_code/snippets/imgproc_calcHist.cpp

@@ -6,7 +6,7 @@ using namespace cv;
 int main( int argc, char** argv )
 {
     Mat src, hsv;
-    if( argc != 2 || !(src=imread(argv[1], 1)).data )
+    if( argc != 2 || !(src=imread(argv[1], IMREAD_COLOR)).data )
         return -1;
 
     cvtColor(src, hsv, COLOR_BGR2HSV);

samples/cpp/tutorial_code/snippets/imgproc_drawContours.cpp

@@ -9,7 +9,7 @@ int main( int argc, char** argv )
     Mat src;
     // the first command-line parameter must be a filename of the binary
     // (black-n-white) image
-    if( argc != 2 || !(src=imread(argv[1], 0)).data)
+    if( argc != 2 || !(src=imread(argv[1], IMREAD_GRAYSCALE)).data)
         return -1;
 
     Mat dst = Mat::zeros(src.rows, src.cols, CV_8UC3);