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Resample RGB images in C++ #29453

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0e0e71c
Remove unused pixfmt_pre_type
QuLogic Jan 10, 2025
2aca299
Remove unused fixed_blender_rgba_pre
QuLogic Jan 10, 2025
2b73e7e
Resample RGB images in C++
QuLogic Jan 10, 2025
769f7a4
Avoid another copy when RGBA is resampled as RGB
QuLogic Jan 17, 2025
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30 changes: 9 additions & 21 deletions lib/matplotlib/image.py
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Original file line number Diff line number Diff line change
Expand Up @@ -160,8 +160,7 @@ def flush_images():
flush_images()


def _resample(
image_obj, data, out_shape, transform, *, resample=None, alpha=1):
def _resample(image_obj, data, out_shape, transform, *, resample=None, alpha=1):
"""
Convenience wrapper around `._image.resample` to resample *data* to
*out_shape* (with a third dimension if *data* is RGBA) that takes care of
Expand Down Expand Up @@ -204,7 +203,10 @@ def _resample(
interpolation = 'nearest'
else:
interpolation = 'hanning'
out = np.zeros(out_shape + data.shape[2:], data.dtype) # 2D->2D, 3D->3D.
if len(data.shape) == 3:
# Always output RGBA.
out_shape += (4, )
out = np.zeros(out_shape, data.dtype)
if resample is None:
resample = image_obj.get_resample()
_image.resample(data, out, transform,
Expand All @@ -216,20 +218,6 @@ def _resample(
return out


def _rgb_to_rgba(A):
"""
Convert an RGB image to RGBA, as required by the image resample C++
extension.
"""
rgba = np.zeros((A.shape[0], A.shape[1], 4), dtype=A.dtype)
rgba[:, :, :3] = A
if rgba.dtype == np.uint8:
rgba[:, :, 3] = 255
else:
rgba[:, :, 3] = 1.0
return rgba


class _ImageBase(mcolorizer.ColorizingArtist):
"""
Base class for images.
Expand Down Expand Up @@ -508,10 +496,10 @@ def _make_image(self, A, in_bbox, out_bbox, clip_bbox, magnification=1.0,
# alpha channel below.
output_alpha = (255 * alpha) if A.dtype == np.uint8 else alpha
else:
output_alpha = _resample( # resample alpha channel
self, A[..., 3], out_shape, t, alpha=alpha)
output = _resample( # resample rgb channels
self, _rgb_to_rgba(A[..., :3]), out_shape, t, alpha=alpha)
# resample alpha channel
output_alpha = _resample(self, A[..., 3], out_shape, t, alpha=alpha)
# resample rgb channels
output = _resample(self, A[..., :3], out_shape, t, alpha=alpha)
output[..., 3] = output_alpha # recombine rgb and alpha

# output is now either a 2D array of normed (int or float) data
Expand Down
4 changes: 2 additions & 2 deletions lib/matplotlib/tests/test_image.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1577,8 +1577,8 @@ def test__resample_valid_output():
resample(np.zeros((9, 9)), np.zeros((9, 9, 4)))
with pytest.raises(ValueError, match="different dimensionalities"):
resample(np.zeros((9, 9, 4)), np.zeros((9, 9)))
with pytest.raises(ValueError, match="3D input array must be RGBA"):
resample(np.zeros((9, 9, 3)), np.zeros((9, 9, 4)))
with pytest.raises(ValueError, match="3D input array must be RGB"):
resample(np.zeros((9, 9, 2)), np.zeros((9, 9, 4)))
with pytest.raises(ValueError, match="3D output array must be RGBA"):
resample(np.zeros((9, 9, 4)), np.zeros((9, 9, 3)))
with pytest.raises(ValueError, match="mismatched types"):
Expand Down
90 changes: 55 additions & 35 deletions src/_image_resample.h
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@
#include "agg_image_accessors.h"
#include "agg_path_storage.h"
#include "agg_pixfmt_gray.h"
#include "agg_pixfmt_rgb.h"
#include "agg_pixfmt_rgba.h"
#include "agg_renderer_base.h"
#include "agg_renderer_scanline.h"
Expand All @@ -16,6 +17,7 @@
#include "agg_span_allocator.h"
#include "agg_span_converter.h"
#include "agg_span_image_filter_gray.h"
#include "agg_span_image_filter_rgb.h"
#include "agg_span_image_filter_rgba.h"
#include "agg_span_interpolator_adaptor.h"
#include "agg_span_interpolator_linear.h"
Expand Down Expand Up @@ -496,16 +498,39 @@ typedef enum {
} interpolation_e;


// T is rgba if and only if it has an T::r field.
// T is rgb(a) if and only if it has an T::r field.
template<typename T, typename = void> struct is_grayscale : std::true_type {};
template<typename T> struct is_grayscale<T, std::void_t<decltype(T::r)>> : std::false_type {};
template<typename T> constexpr bool is_grayscale_v = is_grayscale<T>::value;


template<typename color_type>
// rgb_step is only used if input_has_alpha=false.
template<typename color_type, bool input_has_alpha, int rgb_step=3>
struct type_mapping
{
using blender_type = std::conditional_t<
using input_blender_type = std::conditional_t<
is_grayscale_v<color_type>,
agg::blender_gray<color_type>,
std::conditional_t<
input_has_alpha,
std::conditional_t<
std::is_same_v<color_type, agg::rgba8>,
fixed_blender_rgba_plain<color_type, agg::order_rgba>,
agg::blender_rgba_plain<color_type, agg::order_rgba>
>,
agg::blender_rgb<color_type, agg::order_rgb>
>
>;
using input_pixfmt_type = std::conditional_t<
is_grayscale_v<color_type>,
agg::pixfmt_alpha_blend_gray<input_blender_type, agg::rendering_buffer>,
std::conditional_t<
input_has_alpha,
agg::pixfmt_alpha_blend_rgba<input_blender_type, agg::rendering_buffer>,
agg::pixfmt_alpha_blend_rgb<input_blender_type, agg::rendering_buffer, rgb_step>
>
>;
using output_blender_type = std::conditional_t<
is_grayscale_v<color_type>,
agg::blender_gray<color_type>,
std::conditional_t<
Expand All @@ -514,36 +539,37 @@ struct type_mapping
agg::blender_rgba_plain<color_type, agg::order_rgba>
>
>;
using pixfmt_type = std::conditional_t<
using output_pixfmt_type = std::conditional_t<
is_grayscale_v<color_type>,
agg::pixfmt_alpha_blend_gray<blender_type, agg::rendering_buffer>,
agg::pixfmt_alpha_blend_rgba<blender_type, agg::rendering_buffer>
>;
using pixfmt_pre_type = std::conditional_t<
is_grayscale_v<color_type>,
pixfmt_type,
agg::pixfmt_alpha_blend_rgba<
std::conditional_t<
std::is_same_v<color_type, agg::rgba8>,
fixed_blender_rgba_pre<color_type, agg::order_rgba>,
agg::blender_rgba_pre<color_type, agg::order_rgba>
>,
agg::rendering_buffer>
agg::pixfmt_alpha_blend_gray<output_blender_type, agg::rendering_buffer>,
agg::pixfmt_alpha_blend_rgba<output_blender_type, agg::rendering_buffer>
>;
template<typename A> using span_gen_affine_type = std::conditional_t<
is_grayscale_v<color_type>,
agg::span_image_resample_gray_affine<A>,
agg::span_image_resample_rgba_affine<A>
std::conditional_t<
input_has_alpha,
agg::span_image_resample_rgba_affine<A>,
agg::span_image_resample_rgb_affine<A>
>
>;
template<typename A, typename B> using span_gen_filter_type = std::conditional_t<
is_grayscale_v<color_type>,
agg::span_image_filter_gray<A, B>,
agg::span_image_filter_rgba<A, B>
std::conditional_t<
input_has_alpha,
agg::span_image_filter_rgba<A, B>,
agg::span_image_filter_rgb<A, B>
>
>;
template<typename A, typename B> using span_gen_nn_type = std::conditional_t<
is_grayscale_v<color_type>,
agg::span_image_filter_gray_nn<A, B>,
agg::span_image_filter_rgba_nn<A, B>
std::conditional_t<
input_has_alpha,
agg::span_image_filter_rgba_nn<A, B>,
agg::span_image_filter_rgb_nn<A, B>
>
>;
};

Expand Down Expand Up @@ -697,16 +723,17 @@ static void get_filter(const resample_params_t &params,
}


template<typename color_type>
// rgb_step is only used if input_has_alpha=false.
template<typename color_type, bool input_has_alpha = true, int rgb_step = 3>
void resample(
const void *input, int in_width, int in_height,
void *output, int out_width, int out_height,
const void *input, int in_width, int in_height, int in_stride,
void *output, int out_width, int out_height, int out_stride,
resample_params_t &params)
{
using type_mapping_t = type_mapping<color_type>;
using type_mapping_t = type_mapping<color_type, input_has_alpha, rgb_step>;

using input_pixfmt_t = typename type_mapping_t::pixfmt_type;
using output_pixfmt_t = typename type_mapping_t::pixfmt_type;
using input_pixfmt_t = typename type_mapping_t::input_pixfmt_type;
using output_pixfmt_t = typename type_mapping_t::output_pixfmt_type;

using renderer_t = agg::renderer_base<output_pixfmt_t>;
using rasterizer_t = agg::rasterizer_scanline_aa<agg::rasterizer_sl_clip_dbl>;
Expand All @@ -722,11 +749,6 @@ void resample(
using arbitrary_interpolator_t =
agg::span_interpolator_adaptor<agg::span_interpolator_linear<>, lookup_distortion>;

size_t itemsize = sizeof(color_type);
if (is_grayscale<color_type>::value) {
itemsize /= 2; // agg::grayXX includes an alpha channel which we don't have.
}

if (params.interpolation != NEAREST &&
params.is_affine &&
fabs(params.affine.sx) == 1.0 &&
Expand All @@ -743,14 +765,12 @@ void resample(
span_conv_alpha_t conv_alpha(params.alpha);

agg::rendering_buffer input_buffer;
input_buffer.attach(
(unsigned char *)input, in_width, in_height, in_width * itemsize);
input_buffer.attach((unsigned char *)input, in_width, in_height, in_stride);
input_pixfmt_t input_pixfmt(input_buffer);
image_accessor_t input_accessor(input_pixfmt);

agg::rendering_buffer output_buffer;
output_buffer.attach(
(unsigned char *)output, out_width, out_height, out_width * itemsize);
output_buffer.attach((unsigned char *)output, out_width, out_height, out_stride);
output_pixfmt_t output_pixfmt(output_buffer);
renderer_t renderer(output_pixfmt);

Expand Down
79 changes: 57 additions & 22 deletions src/_image_wrapper.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -106,14 +106,30 @@ image_resample(py::array input_array,
throw std::invalid_argument("Input array must be a 2D or 3D array");
}

if (ndim == 3 && input_array.shape(2) != 4) {
throw std::invalid_argument(
"3D input array must be RGBA with shape (M, N, 4), has trailing dimension of {}"_s.format(
input_array.shape(2)));
py::ssize_t ncomponents = 0;
int rgb_step = 0;
if (ndim == 3) {
ncomponents = input_array.shape(2);
if (ncomponents == 3) {
// We special-case a few options in order to avoid copying in the common case.
auto rgb_stride = input_array.strides(1);
auto item_stride = input_array.strides(2);
if (rgb_stride == 3 * item_stride) {
rgb_step = 3;
} else if (rgb_stride == 4 * item_stride) {
rgb_step = 4;
}
} else if (ncomponents != 4) {
throw std::invalid_argument(
"3D input array must be RGB with shape (M, N, 3) or RGBA with shape (M, N, 4), "
"has trailing dimension of {}"_s.format(ncomponents));
}
}

// Ensure input array is contiguous, regardless of dtype
input_array = py::array::ensure(input_array, py::array::c_style);
if (rgb_step == 0) {
// Ensure input array is contiguous, regardless of dtype
input_array = py::array::ensure(input_array, py::array::c_style);
}

// Validate output array
auto out_ndim = output_array.ndim();
Expand Down Expand Up @@ -173,25 +189,44 @@ image_resample(py::array input_array,

if (auto resampler =
(ndim == 2) ? (
(dtype.equal(py::dtype::of<std::uint8_t>())) ? resample<agg::gray8> :
(dtype.equal(py::dtype::of<std::int8_t>())) ? resample<agg::gray8> :
(dtype.equal(py::dtype::of<std::uint16_t>())) ? resample<agg::gray16> :
(dtype.equal(py::dtype::of<std::int16_t>())) ? resample<agg::gray16> :
(dtype.equal(py::dtype::of<float>())) ? resample<agg::gray32> :
(dtype.equal(py::dtype::of<double>())) ? resample<agg::gray64> :
dtype.equal(py::dtype::of<std::uint8_t>()) ? resample<agg::gray8> :
dtype.equal(py::dtype::of<std::int8_t>()) ? resample<agg::gray8> :
dtype.equal(py::dtype::of<std::uint16_t>()) ? resample<agg::gray16> :
dtype.equal(py::dtype::of<std::int16_t>()) ? resample<agg::gray16> :
dtype.equal(py::dtype::of<float>()) ? resample<agg::gray32> :
dtype.equal(py::dtype::of<double>()) ? resample<agg::gray64> :
nullptr) : (
// ndim == 3
(dtype.equal(py::dtype::of<std::uint8_t>())) ? resample<agg::rgba8> :
(dtype.equal(py::dtype::of<std::int8_t>())) ? resample<agg::rgba8> :
(dtype.equal(py::dtype::of<std::uint16_t>())) ? resample<agg::rgba16> :
(dtype.equal(py::dtype::of<std::int16_t>())) ? resample<agg::rgba16> :
(dtype.equal(py::dtype::of<float>())) ? resample<agg::rgba32> :
(dtype.equal(py::dtype::of<double>())) ? resample<agg::rgba64> :
nullptr)) {
// ndim == 3
(ncomponents == 4) ? (
dtype.equal(py::dtype::of<std::uint8_t>()) ? resample<agg::rgba8, true> :
dtype.equal(py::dtype::of<std::int8_t>()) ? resample<agg::rgba8, true> :
dtype.equal(py::dtype::of<std::uint16_t>()) ? resample<agg::rgba16, true> :
dtype.equal(py::dtype::of<std::int16_t>()) ? resample<agg::rgba16, true> :
dtype.equal(py::dtype::of<float>()) ? resample<agg::rgba32, true> :
dtype.equal(py::dtype::of<double>()) ? resample<agg::rgba64, true> :
nullptr
) : (
(rgb_step == 4) ? (
dtype.equal(py::dtype::of<std::uint8_t>()) ? resample<agg::rgba8, false, 4> :
dtype.equal(py::dtype::of<std::int8_t>()) ? resample<agg::rgba8, false, 4> :
dtype.equal(py::dtype::of<std::uint16_t>()) ? resample<agg::rgba16, false, 4> :
dtype.equal(py::dtype::of<std::int16_t>()) ? resample<agg::rgba16, false, 4> :
dtype.equal(py::dtype::of<float>()) ? resample<agg::rgba32, false, 4> :
dtype.equal(py::dtype::of<double>()) ? resample<agg::rgba64, false, 4> :
nullptr
) : (
dtype.equal(py::dtype::of<std::uint8_t>()) ? resample<agg::rgba8, false, 3> :
dtype.equal(py::dtype::of<std::int8_t>()) ? resample<agg::rgba8, false, 3> :
dtype.equal(py::dtype::of<std::uint16_t>()) ? resample<agg::rgba16, false, 3> :
dtype.equal(py::dtype::of<std::int16_t>()) ? resample<agg::rgba16, false, 3> :
dtype.equal(py::dtype::of<float>()) ? resample<agg::rgba32, false, 3> :
dtype.equal(py::dtype::of<double>()) ? resample<agg::rgba64, false, 3> :
nullptr))))
{
Py_BEGIN_ALLOW_THREADS
resampler(
input_array.data(), input_array.shape(1), input_array.shape(0),
output_array.mutable_data(), output_array.shape(1), output_array.shape(0),
input_array.data(), input_array.shape(1), input_array.shape(0), input_array.strides(0),
output_array.mutable_data(), output_array.shape(1), output_array.shape(0), output_array.strides(0),
params);
Py_END_ALLOW_THREADS
} else {
Expand Down
40 changes: 0 additions & 40 deletions src/agg_workaround.h
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Original file line number Diff line number Diff line change
Expand Up @@ -8,46 +8,6 @@
blending of RGBA32 pixels does not preserve enough precision
*/

template<class ColorT, class Order>
struct fixed_blender_rgba_pre : agg::conv_rgba_pre<ColorT, Order>
{
typedef ColorT color_type;
typedef Order order_type;
typedef typename color_type::value_type value_type;
typedef typename color_type::calc_type calc_type;
typedef typename color_type::long_type long_type;
enum base_scale_e
{
base_shift = color_type::base_shift,
base_mask = color_type::base_mask
};

//--------------------------------------------------------------------
static AGG_INLINE void blend_pix(value_type* p,
value_type cr, value_type cg, value_type cb,
value_type alpha, agg::cover_type cover)
{
blend_pix(p,
color_type::mult_cover(cr, cover),
color_type::mult_cover(cg, cover),
color_type::mult_cover(cb, cover),
color_type::mult_cover(alpha, cover));
}

//--------------------------------------------------------------------
static AGG_INLINE void blend_pix(value_type* p,
value_type cr, value_type cg, value_type cb,
value_type alpha)
{
alpha = base_mask - alpha;
p[Order::R] = (value_type)(((p[Order::R] * alpha) >> base_shift) + cr);
p[Order::G] = (value_type)(((p[Order::G] * alpha) >> base_shift) + cg);
p[Order::B] = (value_type)(((p[Order::B] * alpha) >> base_shift) + cb);
p[Order::A] = (value_type)(base_mask - ((alpha * (base_mask - p[Order::A])) >> base_shift));
}
};


template<class ColorT, class Order>
struct fixed_blender_rgba_plain : agg::conv_rgba_plain<ColorT, Order>
{
Expand Down
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