Merge pull request #27246 from gursimarsingh:bug_fix/mcc_dnn_dependency

Fix hard dependency of dnn for mcc module. #27246

Currently building objdetect module without dnn fails due to mcc module. This PR makes the dependency optional, by checking if DNN is available in mcc module. 

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [ ] There is a reference to the original bug report and related work
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake

modules/objdetect/src/mcc/checker_detector.cpp

@@ -44,10 +44,13 @@ Ptr<CCheckerDetector> CCheckerDetector::create()
 {
     return makePtr<CCheckerDetectorImpl>();
 }
+
+#ifdef HAVE_OPENCV_DNN
 Ptr<CCheckerDetector> CCheckerDetector::create(const dnn::Net& net)
 {
     return makePtr<CCheckerDetectorImpl>(net);
 }
+#endif
 
 CCheckerDetectorImpl::
     CCheckerDetectorImpl()
@@ -251,6 +254,7 @@ bool CCheckerDetectorImpl::
 {
     m_checkers.clear();
 
+#ifdef HAVE_OPENCV_DNN
     if (this->net.empty() || !m_useDnn)
     {
         return _no_net_process(image, nc, regionsOfInterest);
@@ -471,6 +475,9 @@ bool CCheckerDetectorImpl::
     m_checkers.resize(min(nc, (int)m_checkers.size()));
 
     return !m_checkers.empty();
+#else
+    return _no_net_process(image, nc, regionsOfInterest);
+#endif
 }
 
 
@@ -491,7 +498,7 @@ void CCheckerDetectorImpl::setColorChartType(ColorChart chartType)
 {
     this->m_chartType = chartType;
 }
-
+#ifdef HAVE_OPENCV_DNN
 void CCheckerDetectorImpl::setUseDnnModel(bool useDnn)
 {
     this->m_useDnn = useDnn;
@@ -501,7 +508,7 @@ bool CCheckerDetectorImpl::getUseDnnModel() const
 {
     return m_useDnn;
 }
-
+#endif
 const DetectorParametersMCC& CCheckerDetectorImpl::getDetectionParams() const
 {
     return m_params;
@@ -1428,8 +1435,6 @@ void CCheckerDetectorImpl::
 {
     // color chart classic model
     CChartModel cccm(m_chartType);
-    Mat lab;
-    size_t N;
     std::vector<Point2f> fbox = cccm.box;
     std::vector<Point2f> cellchart = cccm.cellchart;
 
@@ -1439,7 +1444,7 @@ void CCheckerDetectorImpl::
     Mat mask(im_rgb.size(), CV_8U);
     mask.setTo(Scalar::all(0));
     std::vector<Point2f> bch(4), bcht(4);
-    N = cellchart.size() / 4;
+    size_t N = cellchart.size() / 4;
 
     // Create table charts information
     //          |p_size|average|stddev|max|min|

modules/objdetect/src/mcc/checker_detector.hpp

@@ -45,9 +45,11 @@ class CCheckerDetectorImpl : public CCheckerDetector
 
 public:
     CCheckerDetectorImpl();
+#ifdef HAVE_OPENCV_DNN
     CCheckerDetectorImpl(const dnn::Net& _net){
         net = _net;
     }
+#endif
     virtual ~CCheckerDetectorImpl();
 
     bool process(InputArray image, const std::vector<Rect> &regionsOfInterest,
@@ -72,9 +74,11 @@ public:
 
     virtual void setColorChartType(ColorChart chartType) CV_OVERRIDE;
 
+#ifdef HAVE_OPENCV_DNN
     virtual void setUseDnnModel(bool useDnn) CV_OVERRIDE;
 
     virtual bool getUseDnnModel() const CV_OVERRIDE;
+#endif
 
     virtual const DetectorParametersMCC& getDetectionParams() const CV_OVERRIDE;
 
@@ -164,10 +168,14 @@ protected: // methods pipeline
 
 protected:
     std::vector<Ptr<CChecker>> m_checkers;
+#ifdef HAVE_OPENCV_DNN
     dnn::Net net;
+    bool m_useDnn = true;
+#else
+    bool m_useDnn = false;
+#endif
     DetectorParametersMCC m_params = DetectorParametersMCC();
     ColorChart m_chartType;
-    bool m_useDnn = true;
 
 private: // methods aux
     void get_subbox_chart_physical(

modules/objdetect/src/mcc/precomp.hpp

@@ -34,7 +34,9 @@
 #include <opencv2/core.hpp>
 #include <opencv2/imgproc.hpp>
 #include <opencv2/3d.hpp>
+#ifdef HAVE_OPENCV_DNN
 #include <opencv2/dnn.hpp>
+#endif
 
 #include <vector>
 #include <string>