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_png extension loads 16-bit PNGs as 8-bit #915

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Merged
merged 2 commits into from
Jun 5, 2012
Merged

_png extension loads 16-bit PNGs as 8-bit #915

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0e4f3cc
Add 16-bit PNG support to _png module.
mdboom Jun 1, 2012
c2872fa
Fix some problems in the last commit. Use a grayscale image, since m…
mdboom Jun 5, 2012
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4 changes: 2 additions & 2 deletions lib/matplotlib/testing/compare.py
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Original file line number Diff line number Diff line change
Expand Up @@ -210,8 +210,8 @@ def compare_images( expected, actual, tol, in_decorator=False ):
expected = convert(expected)

# open the image files and remove the alpha channel (if it exists)
expectedImage = _png.read_png_uint8( expected )
actualImage = _png.read_png_uint8( actual )
expectedImage = _png.read_png_int( expected )
actualImage = _png.read_png_int( actual )

actualImage, expectedImage = crop_to_same(actual, actualImage, expected, expectedImage)

Expand Down
Binary file added lib/matplotlib/tests/baseline_images/test_png/uint16.png
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10 changes: 10 additions & 0 deletions lib/matplotlib/tests/test_png.py
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Expand Up @@ -3,6 +3,7 @@
import matplotlib.cm as cm
import glob
import os
import numpy as np

@image_comparison(baseline_images=['pngsuite'], extensions=['png'])
def test_pngsuite():
Expand All @@ -25,3 +26,12 @@ def test_pngsuite():

plt.gca().get_frame().set_facecolor("#ddffff")
plt.gca().set_xlim(0, len(files))


def test_imread_png_uint16():
from matplotlib import _png
img = _png.read_png_int(os.path.join(os.path.dirname(__file__),
'baseline_images/test_png/uint16.png'))

assert (img.dtype == np.uint16)
assert np.sum(img.flatten()) == 134184960
54 changes: 45 additions & 9 deletions src/_png.cpp
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Expand Up @@ -48,6 +48,8 @@ class _png_module : public Py::ExtensionModule<_png_module>
"read_png_float(fileobj)");
add_varargs_method("read_png_uint8", &_png_module::read_png_uint8,
"read_png_uint8(fileobj)");
add_varargs_method("read_png_int", &_png_module::read_png_int,
"read_png_int(fileobj)");
initialize("Module to write PNG files");
}

Expand All @@ -57,7 +59,8 @@ class _png_module : public Py::ExtensionModule<_png_module>
Py::Object write_png(const Py::Tuple& args);
Py::Object read_png_uint8(const Py::Tuple& args);
Py::Object read_png_float(const Py::Tuple& args);
PyObject* _read_png(const Py::Object& py_fileobj, const bool float_result);
Py::Object read_png_int(const Py::Tuple& args);
PyObject* _read_png(const Py::Object& py_fileobj, const bool float_result, int result_bit_depth = -1);
};

static void write_png_data(png_structp png_ptr, png_bytep data, png_size_t length)
Expand Down Expand Up @@ -297,7 +300,8 @@ static void read_png_data(png_structp png_ptr, png_bytep data, png_size_t length
}

PyObject*
_png_module::_read_png(const Py::Object& py_fileobj, const bool float_result)
_png_module::_read_png(const Py::Object& py_fileobj, const bool float_result,
int result_bit_depth)
{
png_byte header[8]; // 8 is the maximum size that can be checked
FILE* fp = NULL;
Expand Down Expand Up @@ -502,7 +506,18 @@ _png_module::_read_png(const Py::Object& py_fileobj, const bool float_result)
}
}
} else {
A = (PyArrayObject *) PyArray_SimpleNew(num_dims, dimensions, NPY_UBYTE);
if (result_bit_depth < 0) {
result_bit_depth = bit_depth;
}

if (result_bit_depth == 8) {
A = (PyArrayObject *) PyArray_SimpleNew(num_dims, dimensions, NPY_UBYTE);
} else if (result_bit_depth == 16) {
A = (PyArrayObject *) PyArray_SimpleNew(num_dims, dimensions, NPY_UINT16);
} else {
throw Py::RuntimeError(
"_image_module::readpng: image has unknown bit depth");
}

if (A == NULL)
{
Expand All @@ -518,17 +533,32 @@ _png_module::_read_png(const Py::Object& py_fileobj, const bool float_result)
if (bit_depth == 16)
{
png_uint_16* ptr = &reinterpret_cast<png_uint_16*>(row)[x * dimensions[2]];
for (png_uint_32 p = 0; p < (png_uint_32)dimensions[2]; p++)
{
*(png_byte*)(A->data + offset + p*A->strides[2]) = ptr[p] >> 8;

if (result_bit_depth == 16) {
for (png_uint_32 p = 0; p < (png_uint_32)dimensions[2]; p++)
{
*(png_uint_16*)(A->data + offset + p*A->strides[2]) = ptr[p];
}
} else {
for (png_uint_32 p = 0; p < (png_uint_32)dimensions[2]; p++)
{
*(png_byte*)(A->data + offset + p*A->strides[2]) = ptr[p] >> 8;
}
}
}
else
{
png_byte* ptr = &(row[x * dimensions[2]]);
for (png_uint_32 p = 0; p < (png_uint_32)dimensions[2]; p++)
{
*(png_byte*)(A->data + offset + p*A->strides[2]) = ptr[p];
if (result_bit_depth == 16) {
for (png_uint_32 p = 0; p < (png_uint_32)dimensions[2]; p++)
{
*(png_uint_16*)(A->data + offset + p*A->strides[2]) = ptr[p];
}
} else {
for (png_uint_32 p = 0; p < (png_uint_32)dimensions[2]; p++)
{
*(png_byte*)(A->data + offset + p*A->strides[2]) = ptr[p];
}
}
}
}
Expand Down Expand Up @@ -569,6 +599,12 @@ _png_module::read_png_float(const Py::Tuple& args)

Py::Object
_png_module::read_png_uint8(const Py::Tuple& args)
{
throw Py::RuntimeError("read_png_uint8 is deprecated. Use read_png_int instead.");
}

Py::Object
_png_module::read_png_int(const Py::Tuple& args)
{
args.verify_length(1);
return Py::asObject(_read_png(args[0], false));
Expand Down