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Add rescale_intensity function with test and example.

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This commit is contained in:
Tony S Yu
2011-12-27 10:49:20 -08:00
parent 111a3c1584
commit f5037203f2
4 changed files with 148 additions and 12 deletions
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doc/examples/plot_equalize.py
+29 -11
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@@ -8,10 +8,14 @@ histogram equalization. Histogram equalization enhances contrast by "spreading
out the most frequent intensity values" in an image [1]_. The equalized image
has a roughly linear cumulative distribution function, as shown in this example.
For comparison, this example also shows an image after its intensity levels are
uniformly stretched.
.. [1] http://en.wikipedia.org/wiki/Histogram_equalization
"""
import matplotlib.pyplot as plt
from matplotlib import ticker
from skimage import data
from skimage.util.dtype import dtype_range
@@ -22,35 +26,49 @@ def plot_hist(img, bins=256):
"""Plot histogram and cumulative histogram for image"""
img_cdf, bins = exposure.cumulative_distribution(img, bins)
plt.hist(img.ravel(), bins=bins)
plt.ylabel('Number of pixels')
plt.xlabel('Pixel intensiy')
# Shorten y-tick labels using scientific notation
y_formatter = ticker.ScalarFormatter(useOffset=True)
y_formatter.set_powerlimits((0, 0)) # force use of scientific notation
ax = plt.gca()
ax.yaxis.set_major_formatter(y_formatter)
ax_cdf = plt.twinx()
ax_cdf.plot(bins, img_cdf, 'r')
xmin, xmax = dtype_range[img.dtype.type]
plt.xlim(xmin, xmax)
ax_cdf.set_ylabel('Fraction of total intensity')
img_orig = data.camera()
# squeeze image intensities to lower image contrast
img = img_orig / 5 + 100
img_rescale = exposure.rescale_intensity(img)
img_eq = exposure.equalize(img)
plt.subplot(2, 2, 1)
plt.subplot(2, 3, 1)
plt.imshow(img, cmap=plt.cm.gray, vmin=0, vmax=255)
plt.title('Low contrast input image')
plt.title('Low contrast image')
plt.axis('off')
plt.subplot(2, 2, 2)
plt.subplot(2, 3, 4)
plt.ylabel('Number of pixels')
plot_hist(img)
plt.subplot(2, 2, 3)
plt.imshow(img_eq, cmap=plt.cm.gray, vmin=0, vmax=1)
plt.title('After\nhistogram equalization')
plt.subplot(2, 3, 2)
plt.imshow(img_rescale, cmap=plt.cm.gray, vmin=0, vmax=255)
plt.title('Rescale intensities')
plt.axis('off')
plt.subplot(2, 2, 4)
plot_hist(img_eq)
plt.subplot(2, 3, 5)
plot_hist(img_rescale)
plt.subplots_adjust(left=0.05, hspace=0.25, wspace=0.3, top=0.95, bottom=0.1)
plt.subplot(2, 3, 3)
plt.imshow(img_eq, cmap=plt.cm.gray, vmin=0, vmax=1)
plt.title('Histogram equalization')
plt.axis('off')
plt.subplot(2, 3, 6)
plot_hist(img_eq)
plt.ylabel('Fraction of total intensity')
# prevent overlap of y-axis labels
plt.subplots_adjust(wspace=0.4)
plt.show()