Merge pull request #30369 from ternaus:codex/python-native-byte-order

fix(python): handle non-native NumPy byte order 🤖🤖🤖 - #30369

Python bindings can read non-native-endian NumPy inputs as native bytes, producing incorrect values or NaN. Mark swapped arrays for the existing cast path before constructing `Mat`; this also rejects incompatible output/in-place destinations before writes.

Closes #30368. Targets 4.x so the common bridge fix can be merged into 5.x.

Validation on macOS ARM64, Python 3.11.11, NumPy 2.4.6:
- Built current 4.x and 5.x. Three regression tests cover 20 dtype/layout/output cases; 18 fail before and all pass after. Read-only inputs and rejected destinations remain unchanged.
- 21 native-input timing cells on 4.x, 101 alternating pairs: fixed/baseline median time 0.957–1.005×, identical results. The 5.x check also stayed within 0.971–1.004×.
- Draft: Linux/hosted CI validation remains pending.

### Pull Request Readiness Checklist

- [x] I agree to contribute to the project under Apache 2 License.
- [x] The patch is not based on GPL or other incompatible code.
- [x] The PR targets the appropriate branch.
- [x] The original bug report is linked.
- [x] Regression tests and native-input performance checks are included; no external test data is needed.
- [x] No public API, feature documentation or sample changes are needed.

modules/python/src2/cv2_convert.cpp

@@ -127,7 +127,7 @@ bool pyopencv_to(PyObject* o, Mat& m, const ArgInfo& info)
         return false;
     }
 
-    bool needcopy = false, needcast = false;
+    bool needcopy = !PyArray_ISNOTSWAPPED(oarr), needcast = needcopy;
     int typenum = PyArray_TYPE(oarr), new_typenum = typenum;
     int type = typenum == NPY_UBYTE ? CV_8U :
                typenum == NPY_BYTE ? CV_8S :

modules/python/test/test_numpy_byte_order.py

@@ -0,0 +1,44 @@
+import unittest
+
+import cv2 as cv
+import numpy as np
+
+
+class NumpyByteOrderTest(unittest.TestCase):
+
+    def test_numpy_non_native_byte_order_input(self):
+        for dtype in (np.int16, np.uint16, np.int32, np.int64, np.float16, np.float32, np.float64):
+            for strided in (False, True):
+                native = np.arange(120, dtype=dtype).reshape(10, 12)
+                foreign = native.astype(native.dtype.newbyteorder('S'))
+                if strided:
+                    native = native[:, ::2]
+                    foreign = foreign[:, ::2]
+                foreign.setflags(write=False)
+                before = foreign.tobytes()
+                expected = cv.copyTo(native, None)
+                actual = cv.copyTo(foreign, None)
+                self.assertEqual(actual.dtype, expected.dtype)
+                np.testing.assert_array_equal(actual, expected)
+                self.assertEqual(foreign.tobytes(), before)
+                self.assertFalse(foreign.flags.writeable)
+
+    def test_numpy_non_native_byte_order_normalize(self):
+        for dtype in (np.float32, np.float64):
+            native = np.linspace(0, 1, 120, dtype=dtype).reshape(10, 12)
+            foreign = native.astype(native.dtype.newbyteorder('S'))
+            expected = cv.normalize(native, None, 0, 1, cv.NORM_MINMAX, dtype=cv.CV_32F)
+            actual = cv.normalize(foreign, None, 0, 1, cv.NORM_MINMAX, dtype=cv.CV_32F)
+            np.testing.assert_array_equal(actual, expected)
+
+    def test_numpy_non_native_byte_order_output_rejected(self):
+        for dtype in (np.int16, np.float16, np.float32, np.float64):
+            output = np.full((10, 12), 137, dtype=np.dtype(dtype).newbyteorder('S'))
+            before = output.tobytes()
+            with self.assertRaises(cv.error):
+                cv.utils.dumpInputOutputArray(output)
+            self.assertEqual(output.tobytes(), before)
+
+
+if __name__ == '__main__':
+    unittest.main()