'Estimate the min/max values of *data* by subsampling.'

def quickMinMax(self, data):

    while (data.size > 1000000.0):
        ax = np.argmax(data.shape)
        sl = ([slice(None)] * data.ndim)
        sl[ax] = slice(None, None, 2)
        data = data[sl]
    return (nanmin(data), nanmax(data))
