Q:

noise remains after applying median filter

So I'm apply the median filter to an image, but at the output, there's blue semi-dots appearing. What are they?
This is the output

And the python code for anyone interested
from scipy.ndimage.filters import median_filter
from matplotlib.pylab import imread, imshow, subplot, title, show, get_cmap

img = imread('images/speckle.gif')
new = median_filter(img, 3)

subplot(121); imshow(img, cmap=get_cmap('gray'));
title('The original')
subplot(122); imshow(new, cmap=get_cmap('gray'));
title('Filtered with the median_filter')

show()

A:

Convert the image to gray scale before applying the median filter.

