Add function to guesstimate number of spatial dimensions

skimage/color/__init__.py

@@ -1,4 +1,5 @@
 from .colorconv import (convert_colorspace,
+                        guess_spatial_dimensions,
                         rgb2hsv,
                         hsv2rgb,
                         rgb2xyz,
@@ -45,6 +46,7 @@ from .colorlabel import color_dict, label2rgb
 
 
 __all__ = ['convert_colorspace',
+           'guess_spatial_dimensions',
            'rgb2hsv',
            'hsv2rgb',
            'rgb2xyz',

skimage/color/colorconv.py

@@ -49,6 +49,37 @@ from ..util import dtype
 from skimage._shared.utils import deprecated
 
 
+def guess_spatial_dimensions(image):
+    """Make an educated guess about whether an image has a channels dimension.
+
+    Parameters
+    ----------
+    image : ndarray
+        The input image.
+
+    Returns
+    -------
+    spatial_dims : int or None
+        The number of spatial dimensions of `image`. If ambiguous, the value
+        is `None`.
+
+    Raises
+    ------
+    ValueError
+        If the image array has less than two or more than four dimensions.
+    """
+    if image.ndim == 2:
+        return 2
+    if image.ndim == 3 and image.shape[-1] != 3:
+        return 3
+    if image.ndim == 3 and image.shape[-1] == 3:
+        return None
+    if image.ndim == 4 and image.shape[-1] == 3:
+        return 3
+    else:
+        raise ValueError("Expected 2D, 3D, or 4D array, got %iD." % image.ndim)
+
+
 @deprecated()
 def is_rgb(image):
     """Test whether the image is RGB or RGBA.