Re: [Image-SIG] Remove Noise from a National Weather Service Radar Image (.gif)

[Christopher Barker]

David Berthelot wrote:

What I do is that I use numpy arrays to store images and perform all my math 
stuff on them.

numpy is good for this stuff, particularly if it gets more complicated, but a few comments"

Example:
import Image
import numpy as N
f = Image.open("image.gif")
g = N.array(N.asarray(f))

note: numpy.asarray returns a read-only array, so calling array() on it makes a copy, so that you can change it. You could use N.asarray(f).copy() as well. Since these are 8-bit palleted images, what you get is a uint8 array, not an rbg array.

for y in xrange(g.shape[0]):
  for x in xrange(g.shape[1]):

noise_color = 4
white = 0
g[g == noise_color] = white

and presto -- every noise pixel is now white.

Enclosed is a test script (and sample image) that demos some of this.

By the way, I tried setting the palette of the new image like so:

im2.putpalette(im.palette)





-Chris



--
Christopher Barker, Ph.D.
Oceanographer

Emergency Response Division
NOAA/NOS/OR&R            (206) 526-6959   voice
7600 Sand Point Way NE   (206) 526-6329   fax
Seattle, WA  98115       (206) 526-6317   main reception

chris.bar...@noaa.gov

the glory (or, one of the glories) or numpy is that you don't have to loop, you can operate in the whole array as a unit. As Fredrik said, You'd have to look at the Pallet to see which color is which, but you can do: and it mostly worked, but white can turned into magenta -- can anyone tell me why/ Also, the new gif is twice as big as the old -- is it not compressed the same way?

test_gif.py
Description: application/python

<<inline: ARX_N0R_0.gif>>

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