diff --git a/modules/imgcodecs/src/grfmt_pam.cpp b/modules/imgcodecs/src/grfmt_pam.cpp
index d3d2f90ef0..3dd4605588 100644
--- a/modules/imgcodecs/src/grfmt_pam.cpp
+++ b/modules/imgcodecs/src/grfmt_pam.cpp
@@ -487,7 +487,7 @@ bool  PAMDecoder::readData( Mat& img )
     bool res = false, funcout;
     PaletteEntry palette[256];
     const struct pam_format *fmt = NULL;
-    struct channel_layout layout;
+    struct channel_layout layout = { 0, 0, 0, 0 }; // normalized to 1-channel grey format
 
     /* setting buffer to max data size so scaling up is possible */
     AutoBuffer<uchar> _src(src_elems_per_row * 2);
@@ -506,9 +506,7 @@ bool  PAMDecoder::readData( Mat& img )
             layout.bchan = 0;
             layout.gchan = 1;
             layout.rchan = 2;
-        } else
-            layout.bchan = layout.gchan = layout.rchan = 0;
-        layout.graychan = 0;
+        }
     }
 
     CV_TRY
diff --git a/modules/imgproc/src/thresh.cpp b/modules/imgproc/src/thresh.cpp
index 8cf17aebb1..b25c495f42 100644
--- a/modules/imgproc/src/thresh.cpp
+++ b/modules/imgproc/src/thresh.cpp
@@ -1483,14 +1483,14 @@ double cv::threshold( InputArray _src, OutputArray _dst, double thresh, double m
         imaxval = saturate_cast<ushort>(imaxval);
 
         int ushrt_min = 0;
-        if (ithresh < ushrt_min || ithresh >= USHRT_MAX)
+        if (ithresh < ushrt_min || ithresh >= (int)USHRT_MAX)
         {
             if (type == THRESH_BINARY || type == THRESH_BINARY_INV ||
                ((type == THRESH_TRUNC || type == THRESH_TOZERO_INV) && ithresh < ushrt_min) ||
-               (type == THRESH_TOZERO && ithresh >= USHRT_MAX))
+               (type == THRESH_TOZERO && ithresh >= (int)USHRT_MAX))
             {
-                int v = type == THRESH_BINARY ? (ithresh >= USHRT_MAX ? 0 : imaxval) :
-                        type == THRESH_BINARY_INV ? (ithresh >= USHRT_MAX ? imaxval : 0) :
+                int v = type == THRESH_BINARY ? (ithresh >= (int)USHRT_MAX ? 0 : imaxval) :
+                        type == THRESH_BINARY_INV ? (ithresh >= (int)USHRT_MAX ? imaxval : 0) :
                   /*type == THRESH_TRUNC ? imaxval :*/ 0;
                 dst.setTo(v);
             }
diff --git a/modules/python/bindings/CMakeLists.txt b/modules/python/bindings/CMakeLists.txt
index 037cb9a39d..4226dd853e 100644
--- a/modules/python/bindings/CMakeLists.txt
+++ b/modules/python/bindings/CMakeLists.txt
@@ -38,15 +38,12 @@ ocv_list_filterout(opencv_hdrs "modules/.*_inl\\\\.h*")
 ocv_list_filterout(opencv_hdrs "modules/.*\\\\.details\\\\.h*")
 ocv_list_filterout(opencv_hdrs "modules/.*/detection_based_tracker\\\\.hpp") # Conditional compilation
 
-set(cv2_generated_hdrs
+set(cv2_generated_files
     "${CMAKE_CURRENT_BINARY_DIR}/pyopencv_generated_include.h"
     "${CMAKE_CURRENT_BINARY_DIR}/pyopencv_generated_funcs.h"
     "${CMAKE_CURRENT_BINARY_DIR}/pyopencv_generated_types.h"
     "${CMAKE_CURRENT_BINARY_DIR}/pyopencv_generated_type_reg.h"
     "${CMAKE_CURRENT_BINARY_DIR}/pyopencv_generated_ns_reg.h"
-)
-
-set(cv2_generated_files ${cv2_generated_hdrs}
     "${OPENCV_PYTHON_SIGNATURES_FILE}"
 )
 
@@ -54,18 +51,29 @@ string(REPLACE ";" "\n" opencv_hdrs_ "${opencv_hdrs}")
 file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/headers.txt" "${opencv_hdrs_}")
 add_custom_command(
     OUTPUT ${cv2_generated_files}
-    COMMAND ${PYTHON_DEFAULT_EXECUTABLE} "${PYTHON_SOURCE_DIR}/src2/gen2.py" ${CMAKE_CURRENT_BINARY_DIR} "${CMAKE_CURRENT_BINARY_DIR}/headers.txt"
-    DEPENDS ${PYTHON_SOURCE_DIR}/src2/gen2.py
-    DEPENDS ${PYTHON_SOURCE_DIR}/src2/hdr_parser.py
-    DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/headers.txt
-    DEPENDS ${opencv_hdrs}
+    COMMAND "${PYTHON_DEFAULT_EXECUTABLE}" "${PYTHON_SOURCE_DIR}/src2/gen2.py" "${CMAKE_CURRENT_BINARY_DIR}" "${CMAKE_CURRENT_BINARY_DIR}/headers.txt"
+    DEPENDS "${PYTHON_SOURCE_DIR}/src2/gen2.py"
+            "${PYTHON_SOURCE_DIR}/src2/hdr_parser.py"
+            # not a real build dependency (file(WRITE) result): ${CMAKE_CURRENT_BINARY_DIR}/headers.txt
+            ${opencv_hdrs}
     COMMENT "Generate files for Python bindings and documentation"
 )
 
 add_custom_target(gen_opencv_python_source DEPENDS ${cv2_generated_files})
 
 set(cv2_custom_hdr "${CMAKE_CURRENT_BINARY_DIR}/pyopencv_custom_headers.h")
-file(WRITE ${cv2_custom_hdr} "//user-defined headers\n")
+set(cv2_custom_hdr_str "//user-defined headers\n")
 foreach(uh ${opencv_userdef_hdrs})
-    file(APPEND ${cv2_custom_hdr} "#include \"${uh}\"\n")
+    set(cv2_custom_hdr_str "${cv2_custom_hdr_str}#include \"${uh}\"\n")
 endforeach(uh)
+if(EXISTS "${cv2_custom_hdr}")
+  file(READ "${cv2_custom_hdr}" __content)
+else()
+  set(__content "")
+endif()
+if("${__content}" STREQUAL "${cv2_custom_hdr_str}")
+  # Up-to-date
+else()
+  file(WRITE "${cv2_custom_hdr}" "${cv2_custom_hdr_str}")
+endif()
+unset(__content)