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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OpenSolaris 2009.06 is a cutting edge operating system for enterprises
looking to deploy the next generation of Solaris that includes the latest
innovations from Sun and the OpenSource community. Download a copy and
enjoy capabilities such as Networking, Storage and Virtualization.
Go to: http://p.sf.net/sfu/opensolaris-get
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