import numpy
from pylab import figure, show




class IndexTracker:
    def __init__(self, ax, X):
        self.ax = ax
        ax.set_title('use scroll wheen to navigate images')

        self.X = X
        rows,cols,self.slices = X.shape
        self.ind  = self.slices/2

        self.im = ax.imshow(self.X[:,:,self.ind])
        self.update()

    def onscroll(self, event):
        print event.button, event.step
        if event.button=='up':
            self.ind = numpy.clip(self.ind+1, 0, self.slices-1)
        else:
            self.ind = numpy.clip(self.ind-1, 0, self.slices-1)


        self.update()

    def update(self):
        self.im.set_data(self.X[:,:,self.ind])
        ax.set_ylabel('slice %s'%self.ind)        
        self.im.axes.figure.canvas.draw()


fig = figure()
ax = fig.add_subplot(111)

X = numpy.random.rand(20,20,40)

tracker = IndexTracker(ax, X)



fig.canvas.mpl_connect('scroll_event', tracker.onscroll)
show()