Add example for hough_peaks function

doc/examples/plot_hough_transform.py

@@ -59,7 +59,7 @@ References
 
 '''
 
-from skimage.transform import hough, probabilistic_hough
+from skimage.transform import hough, hough_peaks, probabilistic_hough
 from skimage.filter import canny
 from skimage import data
 
@@ -81,11 +81,11 @@ h, theta, d = hough(image)
 
 plt.figure(figsize=(8, 4))
 
-plt.subplot(121)
+plt.subplot(131)
 plt.imshow(image, cmap=plt.cm.gray)
 plt.title('Input image')
 
-plt.subplot(122)
+plt.subplot(132)
 plt.imshow(np.log(1 + h),
            extent=[np.rad2deg(theta[-1]), np.rad2deg(theta[0]),
                    d[-1], d[0]],
@@ -94,6 +94,14 @@ plt.title('Hough transform')
 plt.xlabel('Angles (degrees)')
 plt.ylabel('Distance (pixels)')
 
+plt.subplot(133)
+plt.imshow(image, cmap=plt.cm.gray)
+rows, cols = image.shape
+for _, angle, dist in zip(*hough_peaks(h, theta, d)):
+    y0 = (dist - 0 * np.cos(angle)) / np.sin(angle)
+    y1 = (dist - cols * np.cos(angle)) / np.sin(angle)
+    plt.plot((0, cols), (y0, y1), '-r')
+plt.axis((0, cols, rows, 0))
 
 # Line finding, using the Probabilistic Hough Transform
 
@@ -121,4 +129,3 @@ for line in lines:
 plt.title('Lines found with PHT')
 plt.axis('image')
 plt.show()
-