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Eric Firing wrote:
> Xavier Gnata wrote:
>> Hi,
>>
>> I'm trying to modify the imshow colormapping on the flight:
>>
>> http://matplotlib.sourceforge.net/api/colors_api.html?highlight=linearsegmentedcolormap#matplotlib.colors.Normalize 
>>
>> "Colormapping typically involves two steps: a data array is first 
>> mapped onto the range 0-1 using an instance of Normalize 
>> <http://matplotlib.sourceforge.net/api/colors_api.html?highlight=linearsegmentedcolormap#matplotlib.colors.Normalize> 
>> or of a subclass; then this number in the 0-1 range is mapped to a 
>> color using an instance of a subclass of Colormap 
>> <http://matplotlib.sourceforge.net/api/colors_api.html?highlight=linearsegmentedcolormap#matplotlib.colors.Colormap>" 
>>
>>
>> How should I modify the way "data array is first mapped onto the 
>> range 0-1"?
>> I would like to map all the values <T1 to 0, all the values>T1 to 1 
>> and use an affine function to map all the others values into ]0,1[. 
>> In a more generic way, how should I modify the way the normalization 
>> step is 
>> <http://matplotlib.sourceforge.net/api/colors_api.html?highlight=linearsegmentedcolormap#matplotlib.colors.Normalize> 
>> performed?
>> I could modify the values to be displayed but it is ugly.
>
> Functions and methods that take cmap kwargs also take norm kwargs; 
> they work together. The Normalize subclass instance passed in via the 
> norm kwarg is what does the mapping of the original data to the 0-1 
> range. For examples, see lib/matplotlib/colors.py, which has the 
> Normalize base class and the LogNorm, BoundaryNorm, and NoNorm 
> subclasses.
>
> Eric
Ok. So I just create class MyNorm(matplotlib.colors.Normalize) and call 
imshow(A,cmap=cmap_xmap(lambda x:x,get_cmap("hot")),norm=MyNorm)
That looks easy :)
Thanks.
Xavier

Xavier Gnata wrote:
> Hi,
> 
> I'm trying to modify the imshow colormapping on the flight:
> 
> http://matplotlib.sourceforge.net/api/colors_api.html?highlight=linearsegmentedcolormap#matplotlib.colors.Normalize
> "Colormapping typically involves two steps: a data array is first mapped 
> onto the range 0-1 using an instance of Normalize 
> <http://matplotlib.sourceforge.net/api/colors_api.html?highlight=linearsegmentedcolormap#matplotlib.colors.Normalize> 
> or of a subclass; then this number in the 0-1 range is mapped to a color 
> using an instance of a subclass of Colormap 
> <http://matplotlib.sourceforge.net/api/colors_api.html?highlight=linearsegmentedcolormap#matplotlib.colors.Colormap>" 
> 
> 
> How should I modify the way "data array is first mapped onto the range 0-1"?
> I would like to map all the values <T1 to 0, all the values>T1 to 1 and 
> use an affine function to map all the others values into ]0,1[. In a 
> more generic way, how should I modify the way the normalization step is 
> <http://matplotlib.sourceforge.net/api/colors_api.html?highlight=linearsegmentedcolormap#matplotlib.colors.Normalize> 
> performed?
> I could modify the values to be displayed but it is ugly.
Functions and methods that take cmap kwargs also take norm kwargs; they 
work together. The Normalize subclass instance passed in via the norm 
kwarg is what does the mapping of the original data to the 0-1 range. 
For examples, see lib/matplotlib/colors.py, which has the Normalize base 
class and the LogNorm, BoundaryNorm, and NoNorm subclasses.
Eric
> 
> 
> It is easy to modify the values of the second step of Colormapping:
> from pylab import *
> from numpy import *
> 
> def G(i,j):
> return exp(-((i-100)**2+(j-100)**2)/50.)
> 
> def cmap_xmap(function,cmapInput):
> cdict = cmapInput._segmentdata.copy()
> function_to_map = lambda x : (function(x[0]), x[1], x[2])
> for key in ('red','green','blue'):
> cdict[key] = map(function_to_map, cdict[key])
> cdict[key].sort()
> return matplotlib.colors.LinearSegmentedColormap('MyMap',cdict,1024)
> 
> A=fromfunction(G,(200,200))
> imshow(A,cmap=cmap_xmap(lambda x:x**60,get_cmap("hot")))
> 
> but it does no help.
> 
> Xavier
> 
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Hi,
I'm trying to modify the imshow colormapping on the flight:
http://matplotlib.sourceforge.net/api/colors_api.html?highlight=linearsegmentedcolormap#matplotlib.colors.Normalize
"Colormapping typically involves two steps: a data array is first mapped 
onto the range 0-1 using an instance of Normalize 
<http://matplotlib.sourceforge.net/api/colors_api.html?highlight=linearsegmentedcolormap#matplotlib.colors.Normalize> 
or of a subclass; then this number in the 0-1 range is mapped to a color 
using an instance of a subclass of Colormap 
<http://matplotlib.sourceforge.net/api/colors_api.html?highlight=linearsegmentedcolormap#matplotlib.colors.Colormap>" 
How should I modify the way "data array is first mapped onto the range 0-1"?
I would like to map all the values <T1 to 0, all the values>T1 to 1 and 
use an affine function to map all the others values into ]0,1[. In a 
more generic way, how should I modify the way the normalization step is 
<http://matplotlib.sourceforge.net/api/colors_api.html?highlight=linearsegmentedcolormap#matplotlib.colors.Normalize> 
performed?
I could modify the values to be displayed but it is ugly.
It is easy to modify the values of the second step of Colormapping:
from pylab import *
from numpy import *
def G(i,j):
 return exp(-((i-100)**2+(j-100)**2)/50.)
def cmap_xmap(function,cmapInput):
 cdict = cmapInput._segmentdata.copy()
 function_to_map = lambda x : (function(x[0]), x[1], x[2])
 for key in ('red','green','blue'):
 cdict[key] = map(function_to_map, cdict[key])
 cdict[key].sort()
 return matplotlib.colors.LinearSegmentedColormap('MyMap',cdict,1024)
A=fromfunction(G,(200,200))
imshow(A,cmap=cmap_xmap(lambda x:x**60,get_cmap("hot")))
but it does no help.
Xavier