ENH: Add color histogram plugin

skimage/viewer/plugins/color_histogram.py

@@ -0,0 +1,68 @@
+import numpy as np
+import matplotlib.pyplot as plt
+
+from skimage import color
+from skimage import exposure
+from .plotplugin import PlotPlugin
+from ..canvastools import RectangleTool
+
+
+class ColorHistogram(PlotPlugin):
+    name = 'Color Histogram'
+
+    def __init__(self, **kwargs):
+        super(ColorHistogram, self).__init__(height=400, **kwargs)
+
+        print self.help()
+
+    def attach(self, image_viewer):
+        super(ColorHistogram, self).attach(image_viewer)
+
+        self.rect_tool = RectangleTool(self.ax, on_release=self.ab_selected)
+        self.lab_image = color.rgb2lab(image_viewer.image)
+
+        # Calculate color histogram in the Lab colorspace:
+        L, a, b = self.lab_image.T
+        left, right = -100, 100
+        ab_extents = [left, right, right, left]
+        bins = np.arange(left, right)
+        hist, x_edges, y_edges = np.histogram2d(a.flatten(), b.flatten(), bins,
+                                                normed=True)
+
+        # Clip bin heights that dominate a-b histogram
+        max_val = pct_total_area(hist, percentile=99)
+        hist = exposure.rescale_intensity(hist, in_range=(0, max_val))
+        self.ax.imshow(hist, extent=ab_extents, cmap=plt.cm.gray)
+
+        self.ax.set_title('Color Histogram')
+        self.ax.set_xlabel('b')
+        self.ax.set_ylabel('a')
+
+    def help(self):
+        helpstr = ("Color Histogram tool:",
+                   "Select region of a-b colorspace to highlight on image.")
+        return '\n'.join(helpstr)
+
+    def ab_selected(self, extents):
+        x0, x1, y0, y1 = extents
+
+        lab_masked = self.lab_image.copy()
+        L, a, b = lab_masked.T
+
+        mask = ((a > y0) & (a < y1)) & ((b > x0) & (b < x1))
+        lab_masked[..., 1:][~mask.T] = 0
+
+        self.image_viewer.image = color.lab2rgb(lab_masked)
+
+
+def pct_total_area(image, percentile=80):
+    """Return threshold value based on percentage of total area.
+
+    The specified percent of pixels less than the given intensity threshold.
+    """
+    idx = int((image.size - 1) * percentile / 100.0)
+    sorted_pixels = np.sort(image.flat)
+    return sorted_pixels[idx]
+
+
+

viewer_examples/plugins/color_histogram.py

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+from skimage.viewer import ImageViewer
+from skimage.viewer.plugins.color_histogram import ColorHistogram
+from skimage import data
+
+
+image = data.load('color.png')
+viewer = ImageViewer(image)
+viewer += ColorHistogram()
+viewer.show()