Merge pull request #373 from luispedro/imread_io_plugin

ENH: Add imread io plugin.

CONTRIBUTORS.txt

@@ -119,4 +119,7 @@
   Perimeter calculation in regionprops.
 
 - Olivier Debeir
-  Rank filters (8- and 16-bits) using sliding window.
+  Rank filters (8- and 16-bits) using sliding window.
+
+- Luis Pedro Coelho
+  imread plugin

skimage/io/_plugins/imread_plugin.ini

@@ -0,0 +1,3 @@
+[imread]
+description = Image reading and writing via imread
+provides = imread, imsave

skimage/io/_plugins/imread_plugin.py

@@ -0,0 +1,44 @@
+__all__ = ['imread', 'imsave']
+
+import numpy as np
+from skimage.utils.dtype import convert
+
+try:
+    import imread as _imread
+except ImportError:
+    raise ImportError("Imread could not be found"
+                      "Please refer to http://pypi.python.org/pypi/imread/ "
+                      "for further instructions.")
+
+def imread(fname, dtype=None):
+    """Load an image from file.
+
+    Parameters
+    ----------
+    fname : str
+        Name of input file
+
+    """
+    im = _imread.imread(fname)
+    if dtype is not None:
+        im = convert(im, dtype)
+    return im
+
+def imsave(fname, arr, format_str=None):
+    """Save an image to disk.
+
+    Parameters
+    ----------
+    fname : str
+        Name of destination file.
+    arr : ndarray of uint8 or uint16
+        Array (image) to save.
+    format_str: str,optional
+        Format to save as. 
+
+    Notes
+    -----
+    Currently, only 8-bit precision is supported.
+    """
+    return _imread.imsave(fname, arr, formatstr=format_str)
+

skimage/io/tests/test_imread.py

@@ -0,0 +1,73 @@
+import os.path
+import numpy as np
+from numpy.testing import *
+from numpy.testing.decorators import skipif
+
+from tempfile import NamedTemporaryFile
+
+from skimage import data_dir
+from skimage.io import imread, imsave, use_plugin, reset_plugins
+
+try:
+    import imread as _imread
+    use_plugin('imread')
+except ImportError:
+    imread_available = False
+else:
+    imread_available = True
+
+
+def teardown():
+    reset_plugins()
+
+
+@skipif(not imread_available)
+def test_imread_flatten():
+    # a color image is flattened
+    img = imread(os.path.join(data_dir, 'color.png'), flatten=True)
+    assert img.ndim == 2
+    assert img.dtype == np.float64
+    img = imread(os.path.join(data_dir, 'camera.png'), flatten=True)
+    # check that flattening does not occur for an image that is grey already.
+    assert np.sctype2char(img.dtype) in np.typecodes['AllInteger']
+
+
+@skipif(not imread_available)
+def test_imread_palette():
+    img = imread(os.path.join(data_dir, 'palette_color.png'))
+    assert img.ndim == 3
+
+
+@skipif(not imread_available)
+def test_bilevel():
+    expected = np.zeros((10, 10), bool)
+    expected[::2] = 1
+
+    img = imread(os.path.join(data_dir, 'checker_bilevel.png'))
+    assert_array_equal(img, expected)
+
+
+class TestSave:
+    def roundtrip(self, x, scaling=1):
+        f = NamedTemporaryFile(suffix='.png')
+        fname = f.name
+        f.close()
+        imsave(fname, x)
+        y = imread(fname)
+
+        assert_array_almost_equal((x * scaling).astype(np.int32), y)
+
+    @skipif(not imread_available)
+    def test_imsave_roundtrip(self):
+        dtype = np.uint8
+        for shape in [(10, 10), (10, 10, 3), (10, 10, 4)]:
+            x = np.ones(shape, dtype=dtype) * np.random.random(shape)
+
+            if np.issubdtype(dtype, float):
+                yield self.roundtrip, x, 255
+            else:
+                x = (x * 255).astype(dtype)
+                yield self.roundtrip, x
+
+if __name__ == "__main__":
+    run_module_suite()