Merge pull request #1670 from odebeir/sprint_example_gamma

Sprint example gamma

doc/examples/plot_log_gamma.py

@@ -0,0 +1,77 @@
+"""
+=================================
+Gamma and log contrast adjustment
+=================================
+
+This example adjusts image contrast by performing a Gamma and a Logarithmic
+correction on the input image.
+
+"""
+import matplotlib
+import matplotlib.pyplot as plt
+import numpy as np
+
+from skimage import data, img_as_float
+from skimage import exposure
+
+matplotlib.rcParams['font.size'] = 8
+
+
+def plot_img_and_hist(img, axes, bins=256):
+    """Plot an image along with its histogram and cumulative histogram.
+
+    """
+    img = img_as_float(img)
+    ax_img, ax_hist = axes
+    ax_cdf = ax_hist.twinx()
+
+    # Display image
+    ax_img.imshow(img, cmap=plt.cm.gray)
+    ax_img.set_axis_off()
+
+    # Display histogram
+    ax_hist.hist(img.ravel(), bins=bins, histtype='step', color='black')
+    ax_hist.ticklabel_format(axis='y', style='scientific', scilimits=(0, 0))
+    ax_hist.set_xlabel('Pixel intensity')
+    ax_hist.set_xlim(0, 1)
+    ax_hist.set_yticks([])
+
+    # Display cumulative distribution
+    img_cdf, bins = exposure.cumulative_distribution(img, bins)
+    ax_cdf.plot(bins, img_cdf, 'r')
+    ax_cdf.set_yticks([])
+
+    return ax_img, ax_hist, ax_cdf
+
+
+# Load an example image
+img = data.moon()
+
+# Gamma
+gamma_corrected = exposure.adjust_gamma(img, 2)
+
+# Logarithmic
+logarithmic_corrected = exposure.adjust_log(img, 1)
+
+# Display results
+fig, axes = plt.subplots(nrows=2, ncols=3, figsize=(8, 5))
+
+ax_img, ax_hist, ax_cdf = plot_img_and_hist(img, axes[:, 0])
+ax_img.set_title('Low contrast image')
+
+y_min, y_max = ax_hist.get_ylim()
+ax_hist.set_ylabel('Number of pixels')
+ax_hist.set_yticks(np.linspace(0, y_max, 5))
+
+ax_img, ax_hist, ax_cdf = plot_img_and_hist(gamma_corrected, axes[:, 1])
+ax_img.set_title('Gamma correction')
+
+ax_img, ax_hist, ax_cdf = plot_img_and_hist(logarithmic_corrected, axes[:, 2])
+ax_img.set_title('Logarithmic correction')
+
+ax_cdf.set_ylabel('Fraction of total intensity')
+ax_cdf.set_yticks(np.linspace(0, 1, 5))
+
+# prevent overlap of y-axis labels
+fig.subplots_adjust(wspace=0.4)
+plt.show()