added support for subtracting pedestal from np.array

python/src/pedestal.hpp

@@ -5,6 +5,7 @@
 
 #include <cstdint>
 #include <filesystem>
+#include <pybind11/numpy.h>
 #include <pybind11/pybind11.h>
 #include <pybind11/stl.h>
 
@@ -12,8 +13,10 @@ namespace py = pybind11;
 
 template <typename SUM_TYPE>
 void define_pedestal_bindings(py::module &m, const std::string &name) {
-    py::class_<Pedestal<SUM_TYPE>>(m, name.c_str())
-        .def(py::init<int, int, int>())
+    auto pedestal =
+        py::class_<Pedestal<SUM_TYPE>>(m, name.c_str(), py::buffer_protocol());
+
+    pedestal.def(py::init<int, int, int>())
         .def(py::init<int, int>())
         .def("mean",
              [](Pedestal<SUM_TYPE> &self) {
@@ -50,6 +53,23 @@ void define_pedestal_bindings(py::module &m, const std::string &name) {
                  *std = self.std();
                  return return_image_data(std);
              })
+        .def(
+            "__array_ufunc__",
+            [](py::object self, py::object ufunc, const std::string &method,
+               py::args inputs, py::kwargs kwargs) -> py::object {
+                if (method != "__call__" || inputs.size() != 2 ||
+                    inputs[1].ptr() != self.ptr() ||
+                    py::cast<std::string>(ufunc.attr("__name__")) !=
+                        "subtract") {
+                    return py::reinterpret_borrow<py::object>(
+                        Py_NotImplemented);
+                }
+
+                auto mean =
+                    py::module_::import("builtins").attr("memoryview")(self);
+                return ufunc(inputs[0], mean, **kwargs);
+            },
+            "Support subtracting a Pedestal from a NumPy array.")
         .def("clear", py::overload_cast<>(&Pedestal<SUM_TYPE>::clear))
         .def_property_readonly("rows", &Pedestal<SUM_TYPE>::rows)
         .def_property_readonly("cols", &Pedestal<SUM_TYPE>::cols)
@@ -84,5 +104,17 @@ void define_pedestal_bindings(py::module &m, const std::string &name) {
                 pedestal.push_no_update(v);
             },
             py::arg().noconvert())
-        .def("update_mean", &Pedestal<SUM_TYPE>::update_mean);
-}
+        .def("update_mean", &Pedestal<SUM_TYPE>::update_mean)
+        .def_buffer([](Pedestal<SUM_TYPE> &self) {
+            auto mean = self.view();
+            return py::buffer_info(
+                const_cast<SUM_TYPE *>(mean.data()), sizeof(SUM_TYPE),
+                py::format_descriptor<SUM_TYPE>::format(), 2,
+                {static_cast<py::ssize_t>(mean.shape(0)),
+                 static_cast<py::ssize_t>(mean.shape(1))},
+                {static_cast<py::ssize_t>(mean.strides()[0] * sizeof(SUM_TYPE)),
+                 static_cast<py::ssize_t>(mean.strides()[1] *
+                                          sizeof(SUM_TYPE))},
+                true);
+        });
+}

python/tests/test_Pedestal.py

@@ -0,0 +1,40 @@
+import numpy as np
+import pytest
+
+from aare import Pedestal_d, Pedestal_f
+
+
+@pytest.mark.parametrize(
+    ("pedestal_type", "expected_dtype"),
+    [(Pedestal_d, np.float64), (Pedestal_f, np.float32)],
+)
+def test_numpy_array_minus_pedestal(pedestal_type, expected_dtype):
+    pedestal = pedestal_type(2, 3)
+    pedestal.push(np.array([[2, 4, 6], [8, 10, 12]], dtype=np.uint16))
+    array = np.array([[12, 14, 16], [18, 20, 22]], dtype=np.uint16)
+
+    result = array - pedestal
+
+    np.testing.assert_array_equal(
+        result, np.array([[10, 10, 10], [10, 10, 10]], dtype=expected_dtype)
+    )
+    assert result.dtype == expected_dtype
+
+
+def test_numpy_array_minus_pedestal_rejects_incompatible_shape():
+    pedestal = Pedestal_d(2, 3)
+    array = np.zeros((2, 2), dtype=np.float64)
+
+    with pytest.raises(ValueError):
+        array - pedestal
+
+
+def test_pedestal_exposes_mean_as_read_only_buffer():
+    pedestal = Pedestal_d(2, 3)
+    pedestal.push(np.array([[2, 4, 6], [8, 10, 12]], dtype=np.uint16))
+
+    mean = np.asarray(pedestal)
+
+    np.testing.assert_array_equal(mean, pedestal.view())
+    assert np.shares_memory(mean, pedestal.view())
+    assert not mean.flags.writeable