Add example script for gabor filter

doc/examples/plot_gabor.py

@@ -0,0 +1,114 @@
+"""
+=============================================
+Gabor filter banks for texture classification
+=============================================
+
+In this example, we will see how to classify textures based on Gabor filter
+banks. Frequency and orientation representations of the Gabor filter are similar
+to those of the human visual system.
+
+The images are filtered using the real parts of various different Gabor filter
+kernels. The mean and variance of the filtered images are then used as features
+for classification, which is based on the least squared error for simplicity.
+
+"""
+
+import matplotlib
+import matplotlib.pyplot as plt
+import numpy as np
+from scipy import ndimage as nd
+from skimage import data
+from skimage.util import img_as_float
+from skimage.filter import gabor_kernel
+
+
+matplotlib.rcParams['font.size'] = 9
+
+
+def compute_feats(image, kernels):
+    feats = np.zeros((len(kernels), 2), dtype=np.double)
+    for k, kernel in enumerate(kernels):
+        filtered = nd.convolve(image, kernel, mode='wrap')
+        feats[k, 0] = filtered.mean()
+        feats[k, 1] = filtered.var()
+    return feats
+
+
+def match(feats, ref_feats):
+    min_error = np.inf
+    min_i = None
+    for i in range(ref_feats.shape[0]):
+        error = np.sum((feats - ref_feats[i, :])**2)
+        if error < min_error:
+            min_error = error
+            min_i = i
+    return min_i
+
+
+# prepare filter bank kernels
+kernels = []
+kernel_params = []
+for theta in range(4):
+    theta = theta / 4. * np.pi
+    for sigma in (1, 3):
+        for frequency in (0.05, 0.25):
+            kernel = np.real(gabor_kernel(sigma, sigma, frequency, theta))
+            kernels.append(kernel)
+            params = 'theta=%d, sigma=%d,\nfrequency=%.2f' % (
+                      theta * 180 / np.pi, sigma, frequency)
+            kernel_params.append(params)
+
+
+brick = img_as_float(data.load('brick.png'))
+grass = img_as_float(data.load('grass.png'))
+wall = img_as_float(data.load('rough-wall.png'))
+image_names = ('brick', 'grass', 'wall')
+
+# prepare refernce features
+ref_feats = np.zeros((3, len(kernels), 2), dtype=np.double)
+ref_feats[0, :, :] = compute_feats(brick, kernels)
+ref_feats[1, :, :] = compute_feats(grass, kernels)
+ref_feats[2, :, :] = compute_feats(wall, kernels)
+
+
+print 'Rotated images matched against references using Gabor filter banks:'
+
+print 'original: brick, rotated: 30deg, match result:',
+feats = compute_feats(nd.rotate(brick, angle=190, reshape=False), kernels)
+print image_names[match(feats, ref_feats)]
+
+print 'original: brick, rotated: 70deg, match result:',
+feats = compute_feats(nd.rotate(brick, angle=70, reshape=False), kernels)
+print image_names[match(feats, ref_feats)]
+
+print 'original: grass, rotated: 145deg, match result:',
+feats = compute_feats(nd.rotate(grass, angle=145, reshape=False), kernels)
+print image_names[match(feats, ref_feats)]
+
+
+# plot a selection of the filter bank kernels
+
+kernels = []
+kernel_params = []
+for theta in (0, 1, 3):
+    theta = theta / 4. * np.pi
+    for frequency in (0.05, 0.1, 0.25):
+        kernel = np.real(gabor_kernel(10, 10, frequency, theta))
+        kernels.append(kernel)
+        params = 'theta=%d, frequency=%.2f' % (theta * 180 / np.pi, frequency)
+        kernel_params.append(params)
+
+
+fig, ((ax1, ax2, ax3), (ax4, ax5, ax6)) = plt.subplots(nrows=2, ncols=3,
+                                                       figsize=(9, 6))
+plt.gray()
+
+fig.text(.5, .95, 'Gabor filter bank kernels',
+         horizontalalignment='center', fontsize=15)
+
+for i, ax in enumerate((ax1, ax2, ax3, ax4, ax5, ax6)):
+    ax.imshow(kernels[i], interpolation='nearest')
+    ax.axis('off')
+    ax.set_title(kernel_params[i])
+
+plt.show()