python - Color values in imshow for matplotlib?

Question

I'd like to know the color value of a point I click on when I use imshow() in matplotlib. Is there a way to find this information through the event handler in matplotlib (the same way as the x,y coordinates of your click are available)? If not, how would I find this information?

Specifically I'm thinking about a case like this:

imshow(np.random.rand(10,10)*255, interpolation='nearest')

Thanks! --Erin

Answer 1

Here's a passable solution. It only works for interpolation = 'nearest'. I'm still looking for a cleaner way to retrieve the interpolated value from the image (rather than rounding the picked x,y and selecting from the original array.) Anyway:

from matplotlib import pyplot as plt
import numpy as np

im = plt.imshow(np.random.rand(10,10)*255, interpolation='nearest')
fig = plt.gcf()
ax = plt.gca()

class EventHandler:
    def __init__(self):
        fig.canvas.mpl_connect('button_press_event', self.onpress)

    def onpress(self, event):
        if event.inaxes!=ax:
            return
        xi, yi = (int(round(n)) for n in (event.xdata, event.ydata))
        value = im.get_array()[xi,yi]
        color = im.cmap(im.norm(value))
        print xi,yi,value,color

handler = EventHandler()

plt.show()