Merge pull request #20383 from dbudniko:dbudniko/mtcnn_1st_pnet_simplification

MTCNN 1st pnet simplification to ensure single graph input

* 1st pnet simplification to ensure single graph input

* address comment from Dmitry M regarding unused variable

modules/gapi/samples/face_detection_mtcnn.cpp

@@ -596,7 +596,6 @@ int main(int argc, char* argv[]) {
     cv::GMat scores[MAX_PYRAMID_LEVELS];
     cv::GArray<custom::Face> nms_p_faces[MAX_PYRAMID_LEVELS];
     cv::GArray<custom::Face> total_faces[MAX_PYRAMID_LEVELS];
-    cv::GArray<custom::Face> faces_init(std::vector<custom::Face>{});
 
     //The very first PNet pyramid layer to init total_faces[0]
     in_resized[0] = cv::gapi::resize(in_originalRGB, level_size[0]);
@@ -605,8 +604,7 @@ int main(int argc, char* argv[]) {
     cv::GArray<custom::Face> faces0 = custom::BuildFaces::on(scores[0], regressions[0], static_cast<float>(scales[0]), conf_thresh_p);
     cv::GArray<custom::Face> final_p_faces_for_bb2squares = custom::ApplyRegression::on(faces0, true);
     cv::GArray<custom::Face> final_faces_pnet0 = custom::BBoxesToSquares::on(final_p_faces_for_bb2squares);
-    nms_p_faces[0] = custom::RunNMS::on(final_faces_pnet0, 0.5f, false);
-    total_faces[0] = custom::AccumulatePyramidOutputs::on(faces_init, nms_p_faces[0]);
+    total_faces[0] = custom::RunNMS::on(final_faces_pnet0, 0.5f, false);
     //The rest PNet pyramid layers to accumlate all layers result in total_faces[PYRAMID_LEVELS - 1]]
     for (int i = 1; i < pyramid_levels; ++i)
     {