Make stitching panoramas reusable after estimating transform once

Stitcher will now make a working copy of the CameraParams object to avoid side effects when composing Panorama.
Makes it possible to estimate transform once and then compose multiple panoramas. Useful for setup with fixed cameras.

modules/stitching/src/stitcher.cpp

@@ -261,6 +261,8 @@ Stitcher::Status Stitcher::composePanorama(InputArrayOfArrays images, OutputArra
     double compose_scale = 1;
     bool is_compose_scale_set = false;
 
+    std::vector<detail::CameraParams> cameras_scaled(cameras_);
+
     UMat full_img, img;
     for (size_t img_idx = 0; img_idx < imgs_.size(); ++img_idx)
     {
@@ -282,16 +284,16 @@ Stitcher::Status Stitcher::composePanorama(InputArrayOfArrays images, OutputArra
             compose_work_aspect = compose_scale / work_scale_;
 
             // Update warped image scale
-            warped_image_scale_ *= static_cast<float>(compose_work_aspect);
-            w = warper_->create((float)warped_image_scale_);
+            float warp_scale = static_cast<float>(warped_image_scale_ * compose_work_aspect);
+            w = warper_->create(warp_scale);
 
             // Update corners and sizes
             for (size_t i = 0; i < imgs_.size(); ++i)
             {
                 // Update intrinsics
-                cameras_[i].focal *= compose_work_aspect;
-                cameras_[i].ppx *= compose_work_aspect;
-                cameras_[i].ppy *= compose_work_aspect;
+                cameras_scaled[i].ppx *= compose_work_aspect;
+                cameras_scaled[i].ppy *= compose_work_aspect;
+                cameras_scaled[i].focal *= compose_work_aspect;
 
                 // Update corner and size
                 Size sz = full_img_sizes_[i];
@@ -302,8 +304,8 @@ Stitcher::Status Stitcher::composePanorama(InputArrayOfArrays images, OutputArra
                 }
 
                 Mat K;
-                cameras_[i].K().convertTo(K, CV_32F);
-                Rect roi = w->warpRoi(sz, K, cameras_[i].R);
+                cameras_scaled[i].K().convertTo(K, CV_32F);
+                Rect roi = w->warpRoi(sz, K, cameras_scaled[i].R);
                 corners[i] = roi.tl();
                 sizes[i] = roi.size();
             }
@@ -324,7 +326,7 @@ Stitcher::Status Stitcher::composePanorama(InputArrayOfArrays images, OutputArra
         LOGLN(" after resize time: " << ((getTickCount() - compositing_t) / getTickFrequency()) << " sec");
 
         Mat K;
-        cameras_[img_idx].K().convertTo(K, CV_32F);
+        cameras_scaled[img_idx].K().convertTo(K, CV_32F);
 
 #if ENABLE_LOG
         int64 pt = getTickCount();