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TST: Calculate RMS and diff image in C++ #29102

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13 changes: 4 additions & 9 deletions lib/matplotlib/testing/compare.py
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,7 @@
from PIL import Image

import matplotlib as mpl
from matplotlib import cbook
from matplotlib import cbook, _image
from matplotlib.testing.exceptions import ImageComparisonFailure

_log = logging.getLogger(__name__)
Expand Down Expand Up @@ -398,7 +398,7 @@ def compare_images(expected, actual, tol, in_decorator=False):

The two given filenames may point to files which are convertible to
PNG via the `.converter` dictionary. The underlying RMS is calculated
with the `.calculate_rms` function.
in a similar way to the `.calculate_rms` function.

Parameters
----------
Expand Down Expand Up @@ -469,17 +469,12 @@ def compare_images(expected, actual, tol, in_decorator=False):
if np.array_equal(expected_image, actual_image):
return None

# convert to signed integers, so that the images can be subtracted without
# overflow
expected_image = expected_image.astype(np.int16)
actual_image = actual_image.astype(np.int16)

rms = calculate_rms(expected_image, actual_image)
rms, abs_diff = _image.calculate_rms_and_diff(expected_image, actual_image)

if rms <= tol:
return None

save_diff_image(expected, actual, diff_image)
Image.fromarray(abs_diff).save(diff_image, format="png")

results = dict(rms=rms, expected=str(expected),
actual=str(actual), diff=str(diff_image), tol=tol)
Expand Down
75 changes: 75 additions & 0 deletions src/_image_wrapper.cpp
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Original file line number Diff line number Diff line change
@@ -1,6 +1,8 @@
#include <pybind11/pybind11.h>
#include <pybind11/numpy.h>

#include <algorithm>

#include "_image_resample.h"
#include "py_converters.h"

Expand Down Expand Up @@ -200,6 +202,76 @@
}


// This is used by matplotlib.testing.compare to calculate RMS and a difference image.
static py::tuple
calculate_rms_and_diff(py::array_t<unsigned char> expected_image,
py::array_t<unsigned char> actual_image)
{
if (expected_image.ndim() != 3) {
auto exceptions = py::module_::import("matplotlib.testing.exceptions");

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auto ImageComparisonFailure = exceptions.attr("ImageComparisonFailure");
py::set_error(
ImageComparisonFailure,
"Expected image must be 3-dimensional, but is {ndim}-dimensional"_s.format(
"ndim"_a=expected_image.ndim()));
throw py::error_already_set();
}

if (actual_image.ndim() != 3) {
auto exceptions = py::module_::import("matplotlib.testing.exceptions");

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auto ImageComparisonFailure = exceptions.attr("ImageComparisonFailure");
py::set_error(
ImageComparisonFailure,
"Actual image must be 3-dimensional, but is {ndim}-dimensional"_s.format(
"ndim"_a=actual_image.ndim()));
throw py::error_already_set();
}

auto height = expected_image.shape(0);
auto width = expected_image.shape(1);
auto depth = expected_image.shape(2);

if (height != actual_image.shape(0) || width != actual_image.shape(1) ||
depth != actual_image.shape(2)) {
auto exceptions = py::module_::import("matplotlib.testing.exceptions");

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auto ImageComparisonFailure = exceptions.attr("ImageComparisonFailure");
py::set_error(
ImageComparisonFailure,
"Image sizes do not match expected size: {expected_image.shape} "_s
"actual size {actual_image.shape}"_s.format(
"expected_image"_a=expected_image, "actual_image"_a=actual_image));
throw py::error_already_set();
}
auto expected = expected_image.unchecked<3>();
auto actual = actual_image.unchecked<3>();

py::ssize_t diff_dims[3] = {height, width, 3};
py::array_t<unsigned char> diff_image(diff_dims);
auto diff = diff_image.mutable_unchecked<3>();

double total = 0.0;
for (auto i = 0; i < height; i++) {
for (auto j = 0; j < width; j++) {
for (auto k = 0; k < depth; k++) {
auto pixel_diff = static_cast<double>(expected(i, j, k)) -
static_cast<double>(actual(i, j, k));

total += pixel_diff*pixel_diff;

if (k != 3) { // Hard-code a fully solid alpha channel by omitting it.
diff(i, j, k) = static_cast<unsigned char>(std::clamp(
abs(pixel_diff) * 10, // Expand differences in luminance domain.
0.0, 255.0));
}
}
}
}
total = total / (width * height * depth);

return py::make_tuple(sqrt(total), diff_image);
}


PYBIND11_MODULE(_image, m, py::mod_gil_not_used())
{
py::enum_<interpolation_e>(m, "_InterpolationType")
Expand Down Expand Up @@ -232,4 +304,7 @@
"norm"_a = false,
"radius"_a = 1,
image_resample__doc__);

m.def("calculate_rms_and_diff", &calculate_rms_and_diff,
"expected_image"_a, "actual_image"_a);
}
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