[Matplotlib-users] Luts in matplotlib ...

[Eric E. <ems...@ob...>]

HI again,

I have questions of how to generate new LUTs outside matplotlib.

3 main issues:

1/ how to create a new lut in the same way that cm.py/colors.py is doing it
   in matplotlib
2/ how to create a new lut which is given by a set of e.g., 256 colours 
levels (R, G, B)
  but not as a segmented array as in cm/colors
3/ How do you rescale a lut without rescaling the array itself?
(so an equivalent to load/itt log for example in Midas for those who know).
   For example I would like to use the jet lut but with a log increase
  of the lut so that e.g. displaying the color bar shows it is in ''log''

For 1, I am not so sure what to do, and for 2/ I give below
what I am doing at the moment. To be frank, it looks quite ugly
(mainly because I am a bad programmer and don't know so much about
python/matplotlib).

I got inspired by cm and colors.py and Midas lut
but really this is probably not the way to go.
In order to change the lut I just then do:

lut('mylut')

where 'mylut.lasc' is then the ascii file where the 256 colours are 
given in 3 columns
(R G B) of 256 rows

The problem is that since I do not have the corresponding segmented 
array for each
lut (and I don't want it to be that way) I need to define a ''dummy'' array.
Then each time I use imshow I must reload the lut (otherwise it uses 
this dummy segmented
array which is here a gray lut).

I am not sure this is all clear, but basically what I am trying to do 
here is to just
answer questions 1, 2, 3  above and below is an ugly solution for 2 (but 
incomplete).

Any help is welcome. Thanks.

Eric
#########################################################################################
"""######################################
   # MIDAS-LIKE LUT and ITT ??
   ######################################"""
_dummy_data =  {'red':   ((0., 0, 0), (1., 1, 1)),
               'green': ((0., 0, 0), (1., 1, 1)),
               'blue':  ((0., 0, 0), (1., 1, 1))}

class myMidasLut(colors.LinearSegmentedColormap):
   """   Definition of luts a la Midas, with R, G, and B levels
   """
   def __init__(self, name='grey', alpha=1.0):
      self.LUT_PATH = '/softwares/python/pycral/midaslut/'
      self._red_lut = arange(256)/255.
      self._green_lut = arange(256)/255.
      self._blue_lut = arange(256)/255.
      self._isinit = True
      self.name = name
      self.N = 256
      cm.datad[name] = _dummy_data

   def new(self,name, alpha=1.0):  
      sname = str(name)
      sname = self.LUT_PATH+sname+".lasc"
      if os.path.isfile(sname):
         f = open(sname)
         list = f.readlines()
         for i in range(256):
            self._red_lut[i] = float(list[i].split()[0])
            self._green_lut[i] = float(list[i].split()[1])
            self._blue_lut[i] = float(list[i].split()[2])
         f.close
         self.name = name
      else :
         print 'ERROR: Lut file', name,'does not exist'

      rc('image', cmap=name)
      im = gci()
      if im is not None:
         im.set_cmap(self)
         im.set_alpha(alpha)
         draw_if_interactive()

      cm.datad[name] = _dummy_data
   
################ Default Lut initialisation ##
pglut = myMidasLut()

################ Function to change the lut ##
def lut (name, alpha=1.0) :
   pglut.new(name, alpha)

#########################################################################################

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