Plugin framework for image I/O.

scikits/image/io/__init__.py

@@ -1,7 +1,9 @@
 """Utilities to read and write images in various formats."""
 
+import pil_plugin
+import matplotlib_plugin
 
-from pil_imread import *
+from io import *
+from plugin import register as register_plugin
 from sift import *
 from collection import *
-

scikits/image/io/io.py

@@ -0,0 +1,107 @@
+from scikits.image.io.plugin import plugin_store
+
+def _call_plugin(kind, *args, **kwargs):
+    if not kind in plugin_store:
+        raise ValueError('Invalid function (%s) requested.' % kind)
+
+    plugin_funcs = plugin_store[kind]
+    if len(plugin_funcs) == 0:
+        raise RuntimeError('No suitable plugin registered for %s' % kind)
+
+    plugin = kwargs.pop('plugin', None)
+    if plugin is None:
+        _, func = plugin_funcs[0]
+    else:
+        try:
+            func = [f for (p,f) in plugin_funcs if p == plugin][0]
+        except IndexError:
+            raise RuntimeError('Could not find the plugin "%s" for %s.' % \
+                               (plugin, kind))
+
+    return func(*args, **kwargs)
+
+def imread(fname, as_grey=False, dtype=None, plugin=None, flatten=None,
+           **plugin_args):
+    """Load an image from file.
+
+    Parameters
+    ----------
+    fname : string
+        Image file name, e.g. ``test.jpg``.
+    as_grey : bool
+        If True, convert color images to grey-scale. If `dtype` is not given,
+        converted color images are returned as 32-bit float images.
+        Images that are already in grey-scale format are not converted.
+    dtype : dtype, optional
+        NumPy data-type specifier. If given, the returned image has this type.
+        If None (default), the data-type is determined automatically.
+    plugin : str
+        Name of plugin to use.  By default, the different plugins are
+        tried (starting with the Python Imaging Library) until a suitable
+        candidate is found.
+
+    Other Parameters
+    ----------------
+    flatten : bool
+        Backward compatible keyword, superseded by `as_grey`.
+
+    Returns
+    -------
+    img_array : ndarray
+        The different colour bands/channels are stored in the
+        third dimension, such that a grey-image is MxN, an
+        RGB-image MxNx3 and an RGBA-image MxNx4.
+
+    Other parameters
+    ----------------
+    plugin_args : keywords
+        Passed to the given plugin.
+
+    """
+    # Backward compatibility
+    if flatten is not None:
+        as_grey = flatten
+
+    _call_plugin('read', as_grey, dtype, plugin=plugin, **plugin_args)
+
+def imsave(fname, arr, plugin=None, **plugin_args):
+    """Save an image to file.
+
+    Parameters
+    ----------
+    fname : str
+        Target filename.
+    arr : ndarray of shape (M,N) or (M,N,3) or (M,N,4)
+        Image data.
+    plugin : str
+        Name of plugin to use.  By default, the different plugins are
+        tried (starting with the Python Imaging Library) until a suitable
+        candidate is found.
+
+    Other parameters
+    ----------------
+    plugin_args : keywords
+        Passed to the given plugin.
+
+    """
+    _call_plugin('save', fname, arr, plugin=plugin, **plugin_args)
+
+def imshow(arr, plugin=None, **plugin_args):
+    """Display an image.
+
+    Parameters
+    ----------
+    arr : ndarray
+        Image data.
+    plugin : str
+        Name of plugin to use.  By default, the different plugins are
+        tried (starting with the Python Imaging Library) until a suitable
+        candidate is found.
+
+    Other parameters
+    ----------------
+    plugin_args : keywords
+        Passed to the given plugin.
+
+    """
+    _call_plugin('show', arr, plugin=None, **plugin_args)

scikits/image/io/matplotlib_plugin.py

@@ -0,0 +1,8 @@
+import plugin
+
+try:
+    import matplotlib.pyplot as plt
+except ImportError:
+    pass
+else:
+    plugin.register('matplotlib', show=plt.imshow, save=plt.imsave)

scikits/image/io/pil_imread.py

@@ -1,39 +0,0 @@
-__all__ = ['imread']
-
-import numpy as np
-
-def imread(fname, flatten=False, dtype=None):
-    """Load an image from file.
-
-    Parameters
-    ----------
-    fname : string
-        Image file name, e.g. ``test.jpg``.
-    flatten : bool
-        If True, convert color images to grey-scale. If `dtype` is not given,
-        converted color images are returned as 32-bit float images.
-        Images that are already in grey-scale format are not converted.
-    dtype : dtype, optional
-        NumPy data-type specifier. If given, the returned image has this type.
-        If None (default), the data-type is determined automatically.
-
-    Returns
-    -------
-    img_array : ndarray
-        The different colour bands/channels are stored in the
-        third dimension, such that a grey-image is MxN, an
-        RGB-image MxNx3 and an RGBA-image MxNx4.
-
-    """
-    try:
-        from PIL import Image
-    except ImportError:
-        raise ImportError("Could not import the Python Imaging Library (PIL)"
-                          " required to load image files.  Please refer to"
-                          " http://pypi.python.org/pypi/PIL/ for installation"
-                          " instructions.")
-
-    im = Image.open(fname)
-    if flatten and not im.mode in ('1', 'L', 'I', 'F', 'I;16', 'I;16L', 'I;16B'):
-        im = im.convert('F')
-    return np.array(im, dtype=dtype)

scikits/image/io/pil_plugin.py

@@ -0,0 +1,23 @@
+__all__ = ['imread']
+
+import numpy as np
+import plugin
+
+try:
+    from PIL import Image
+    has_pil = True
+except ImportError:
+    has_pil = False
+
+def imread(fname, as_grey=False, dtype=None):
+    """Load an image from file.
+
+    """
+    im = Image.open(fname)
+    if as_grey and \
+           not im.mode in ('1', 'L', 'I', 'F', 'I;16', 'I;16L', 'I;16B'):
+        im = im.convert('F')
+    return np.array(im, dtype=dtype)
+
+if has_pil:
+    plugin.register('PIL', read=imread)

scikits/image/io/plugin.py

@@ -0,0 +1,37 @@
+"""Handle image reading, writing and plotting plugins.
+
+"""
+
+plugin_store = {'read': [],
+                'save': [],
+                'show': []}
+
+def register(name, **kwds):
+    """Register an image I/O plugin.
+
+    Parameters
+    ----------
+    name : str
+        Name of this plugin.
+    read : callable, optional
+        Function with signature
+        ``read(filename, as_grey=False, dtype=None, **plugin_specific_args)``
+        that reads images.
+    save : callable, optional
+        Function with signature
+        ``write(filename, arr, **plugin_specific_args)``
+        that writes an image to disk.
+    show : callable, optional
+        Function with signature
+        ``show(X, **plugin_specific_args)`` that displays an image.
+
+    """
+    for kind in kwds:
+        if kind not in plugin_store.keys():
+            raise ValueError('Tried to register invalid plugin method.')
+
+        func = kwds[kind]
+        if not callable(func):
+            raise ValueError('Can only register functions as plugins.')
+
+        plugin_store[kind].append((name, func))