build: fix MSVS2017 warning

modules/calib3d/src/fisheye.cpp

@@ -928,7 +928,7 @@ double cv::fisheye::stereoCalibrate(InputArrayOfArrays objectPoints, InputArrayO
     intrinsicRight_errors.isEstimate = intrinsicRight.isEstimate;
 
     std::vector<uchar> selectedParams;
-    std::vector<int> tmp(6 * (n_images + 1), 1);
+    std::vector<uchar> tmp(6 * (n_images + 1), 1);
     selectedParams.insert(selectedParams.end(), intrinsicLeft.isEstimate.begin(), intrinsicLeft.isEstimate.end());
     selectedParams.insert(selectedParams.end(), intrinsicRight.isEstimate.begin(), intrinsicRight.isEstimate.end());
     selectedParams.insert(selectedParams.end(), tmp.begin(), tmp.end());

modules/core/src/command_line_parser.cpp

@@ -69,9 +69,14 @@ static const char* get_type_name(int type)
     return "unknown";
 }
 
+// std::tolower is int->int
+static char char_tolower(char ch)
+{
+    return (char)std::tolower((int)ch);
+}
 static bool parse_bool(std::string str)
 {
-    std::transform(str.begin(), str.end(), str.begin(), ::tolower);
+    std::transform(str.begin(), str.end(), str.begin(), char_tolower);
     std::istringstream is(str);
     bool b;
     is >> (str.size() > 1 ? std::boolalpha : std::noboolalpha) >> b;

modules/core/src/ocl.cpp

@@ -993,6 +993,11 @@ static cl_device_id selectOpenCLDevice()
     return NULL;
 }
 #else
+// std::tolower is int->int
+static char char_tolower(char ch)
+{
+    return (char)std::tolower((int)ch);
+}
 static cl_device_id selectOpenCLDevice()
 {
     std::string platform, deviceName;
@@ -1077,7 +1082,7 @@ static cl_device_id selectOpenCLDevice()
     {
         int deviceType = 0;
         std::string tempStrDeviceType = deviceTypes[t];
-        std::transform( tempStrDeviceType.begin(), tempStrDeviceType.end(), tempStrDeviceType.begin(), tolower );
+        std::transform(tempStrDeviceType.begin(), tempStrDeviceType.end(), tempStrDeviceType.begin(), char_tolower);
 
         if (tempStrDeviceType == "gpu" || tempStrDeviceType == "dgpu" || tempStrDeviceType == "igpu")
             deviceType = Device::TYPE_GPU;

modules/stitching/src/exposure_compensate.cpp

@@ -63,7 +63,7 @@ void ExposureCompensator::feed(const std::vector<Point> &corners, const std::vec
 {
     std::vector<std::pair<UMat,uchar> > level_masks;
     for (size_t i = 0; i < masks.size(); ++i)
-        level_masks.push_back(std::make_pair(masks[i], 255));
+        level_masks.push_back(std::make_pair(masks[i], (uchar)255));
     feed(corners, images, level_masks);
 }