Add NTSC color space.

Also a typo in rgbcie fixed.

scikits/image/color/colorconv.py

@@ -18,6 +18,7 @@ Supported color spaces
 - HSV
 - RGB CIE
 - XYZ
+- NTSC
 
 Authors
 -------
@@ -31,7 +32,8 @@ Authors
 
 from __future__ import division
 
-__all__ = ['rgb2hsv', 'hsv2rgb', 'rgb2xyz', 'xyz2rgb']
+__all__ = ['rgb2hsv', 'hsv2rgb', 'rgb2xyz', 'xyz2rgb', 'rgb2rgbcie', 'rgbcie2rgb',
+           'rgb2ntsc', 'ntsc2rgb']
 __docformat__ = "restructuredtext en"
 
 import numpy as np
@@ -208,7 +210,19 @@ rgbcie_from_xyz = linalg.inv(xyz_from_rgbcie)
 
 # construct matrices to and from rgb:
 rgbcie_from_rgb = np.dot(rgbcie_from_xyz, xyz_from_rgb)
-rgb_from_rgbcie = np.dot(rgb_from_xyz, xyz_from_rgb)
+rgb_from_rgbcie = np.dot(rgb_from_xyz, xyz_from_rgbcie)
+
+# from Travis' code. "Matrices from Jain". TODO: find reference.
+ntsc_from_xyz = np.array([[1.910, -0.533, -0.288],
+                          [-0.985, 2.000, -0.028],
+                          [0.058, -0.118, 0.896]])
+
+xyz_from_ntsc = linalg.inv(ntsc_from_xyz)
+
+# construct matrices to and from rgb:
+ntsc_from_rgb = np.dot(ntsc_from_xyz, xyz_from_rgb)
+rgb_from_ntsc = np.dot(rgb_from_xyz, xyz_from_ntsc)
+
 
 #-------------------------------------------------------------
 # The conversion functions that make use of the matrices above
@@ -384,3 +398,70 @@ def rgbcie2rgb(rgbcie):
     """
     return _convert(rgb_from_rgbcie, rgbcie)
 
+def rgb2ntsc(rgb):
+    """RGB to NTSC color space conversion.
+
+    Parameters
+    ----------
+    rgb : ndarray
+        The image in RGB format, in a 3-D array of shape (.., .., 3).
+
+    Returns
+    -------
+    out : ndarray
+        The image in NTSC format, in a 3-D array of shape (.., .., 3).
+
+    Raises
+    ------
+    ValueError
+        If `rgb` is not a 3-D array of shape (.., .., 3).
+
+    References
+    ----------
+    .. [1] http://en.wikipedia.org/wiki/NTSC
+
+    Examples
+    --------
+    >>> import os
+    >>> from scikits.image import data_dir
+    >>> from scikits.image.io import imread
+
+    >>> lena = imread(os.path.join(data_dir, 'lena.png'))
+    >>> lena_ntsc = rgb2ntsc(lena)
+    """
+    return _convert(ntsc_from_rgb, rgb)
+
+def ntsc2rgb(ntsc):
+    """NTSC to RGB color space conversion.
+
+    Parameters
+    ----------
+    ntsc : ndarray
+        The image in NTSC format, in a 3-D array of shape (.., .., 3).
+
+    Returns
+    -------
+    out : ndarray
+        The image in RGB format, in a 3-D array of shape (.., .., 3).
+
+    Raises
+    ------
+    ValueError
+        If `ntsc` is not a 3-D array of shape (.., .., 3).
+
+    References
+    ----------
+    .. [1] http://en.wikipedia.org/wiki/NTSC
+
+    Examples
+    --------
+    >>> import os
+    >>> from scikits.image import data_dir
+    >>> from scikits.image.io import imread
+
+    >>> lena = imread(os.path.join(data_dir, 'lena.png'))
+    >>> lena_ntsc = rgb2ntsc(lena)
+    >>> lena_rgb = ntsc2rgb(lena_hsv)
+    """
+    return _convert(rgb_from_ntsc, ntsc)
+

scikits/image/color/tests/test_colorconv.py

@@ -18,10 +18,10 @@ from numpy.testing import *
 
 from scikits.image.io import imread
 from scikits.image.color import (
-    rgb2hsv,
-    hsv2rgb,
-    rgb2xyz,
-    xyz2rgb
+    rgb2hsv, hsv2rgb,
+    rgb2xyz, xyz2rgb,
+    rgb2rgbcie, rgbcie2rgb,
+    rgb2ntsc, ntsc2rgb
     )
 
 from scikits.image import data_dir
@@ -91,7 +91,6 @@ class TestColorconv(TestCase):
                         [ 0.35758 ,  0.71516 ,  0.119193],
                         [ 0.412453,  0.212671,  0.019334],
                         [ 0.      ,  0.      ,  0.      ]]])
-
         assert_almost_equal(rgb2xyz(self.colbars_array), gt)
 
     # stop repeating the "raises" checks for all other functions that are
@@ -113,6 +112,48 @@ class TestColorconv(TestCase):
                             self.colbars_array)
 
 
+    # RGB to RGB CIE
+    def test_rgb2rgbcie_conversion(self):
+        gt = np.array([[[ 0.1488856 ,  0.18288098,  0.19277574],
+                        [ 0.01163224,  0.16649536,  0.18948516],
+                        [ 0.12259182,  0.03308008,  0.17298223],
+                        [-0.01466154,  0.01669446,  0.16969164]],
+                       [[ 0.16354714,  0.16618652,  0.0230841 ],
+                        [ 0.02629378,  0.1498009 ,  0.01979351],
+                        [ 0.13725336,  0.01638562,  0.00329059],
+                        [ 0.        ,  0.        ,  0.        ]]])
+        assert_almost_equal(rgb2rgbcie(self.colbars_array), gt)
+
+
+    # RGB CIE to RGB
+    def test_rgbcie2rgb_conversion(self):
+        # only roundtrip test, we checked rgb2rgbcie above already
+        assert_almost_equal(rgbcie2rgb(rgb2rgbcie(self.colbars_array)),
+                            self.colbars_array)
+
+
+    # RGB to NTSC
+    def test_rgb2ntsc_conversion(self):
+        gt = np.array([[[ 0.96880981,  1.03331573,  0.91265003],
+                        [ 0.29994641,  1.01478128,  0.89649967],
+                        [ 0.70133987, -0.04145057,  0.86950234],
+                        [ 0.03247648, -0.05998501,  0.85335198]],
+                       [[ 0.93633333,  1.09330074,  0.05929805],
+                        [ 0.26746994,  1.0747663 ,  0.04314769],
+                        [ 0.66886339,  0.01853444,  0.01615036],
+                        [ 0.        ,  0.        ,  0.        ]]])
+        assert_almost_equal(rgb2ntsc(self.colbars_array), gt)
+
+
+    # NTSC to RGB
+    def test_ntsc2rgb_conversion(self):
+        # only roundtrip test, we checked rgb2ntsc above already
+        assert_almost_equal(ntsc2rgb(rgb2ntsc(self.colbars_array)),
+                            self.colbars_array)
+
+
+
+
 if __name__ == "__main__":
     run_module_suite()