[Numpy-discussion] Using where with tuples

Frank Peacock frank@gis4weather....
Fri Apr 10 19:28:13 CDT 2009


Hello

 

I am trying to use the where function on a numpy array which was obtained
from an image using the asarray function. The code is as follows:

 

from numpy import *

from Image import *

im=open("a.gif")

im2=im.convert("RGBA")

a2 = asarray(im2,uint8)

c = zeros((140,90,4),uint8)

c[:,:] = [0,0,0,255]

b=where(a2[:,:]==(255,0,0,255),c,a2)

c=fromarray(b,"RGBA")

c.save("c.gif")

 

I am trying to convert only red colours to black but although this works it
also converts other tuples as well. How do I ensure that the tuple condition
is enforced exactly, i.e. only on red colours?

 

Thanks

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