problem of cm.get_cmap('gist_rainbow',256)

Community matplotlib-users
1

Hi Everyone,

I am trying the matplotlib. I have to say this is a powerful package for
scientific 2-D plotting. However, I encountered some problems when try
to generate several colormaps.

for example:
a=cm.get_cmap('gist_rainbow',256)(range(256))
will give a error:
Traceback (most recent call last):
File "<pyshell#82>", line 1, in <module>
a=cm.get_cmap('gist_rainbow',256)(range(256))
File "...\site-packages\matplotlib\colors.py", line 498, in __call__
if not self._isinit: self._init()
File "...\site-packages\matplotlib\colors.py", line 649, in _init
self._segmentdata['red'], self._gamma)
TypeError: tuple indices must be integers, not str

but other colormaps can actually work:
a=cm.get_cmap('gist_stern',256)(range(256))

a

array([[ 0. , 0. , 0. , 1. ],
[ 0.0716923 , 0.00392157, 0.00784314, 1. ],
[ 0.14338459, 0.00784314, 0.01568627, 1. ],
...,
[ 0.99215686, 0.99215686, 0.97040326, 1. ],
[ 0.99607843, 0.99607843, 0.98520163, 1. ],
[ 1. , 1. , 1. , 1. ]])

I tried all possible colormaps and found out: gist_rainbow, terrain,
bwr, brg, and seismic will generate the same error, all other colormaps
are OK. I wonder is this a bug or expected behavior?

···

###############################
##matplotlib verison : '1.0.svn'

maps=[m for m in cm.datad if not m.endswith("_r")]
for i in maps:

try:
a=cm.get_cmap(i,256)(range(256))
except:
(type, value, traceback) = sys.exc_info()
print "Problems to create %s" % (i,)
print "The error was --> %s: %s" % (type, value)

Problems to create gist_rainbow
The error was --> <type 'exceptions.TypeError'>: tuple indices must be
integers, not str
Problems to create terrain
The error was --> <type 'exceptions.TypeError'>: tuple indices must be
integers, not str
Problems to create bwr
The error was --> <type 'exceptions.TypeError'>: tuple indices must be
integers, not str
Problems to create brg
The error was --> <type 'exceptions.TypeError'>: tuple indices must be
integers, not str
Problems to create seismic
The error was --> <type 'exceptions.TypeError'>: tuple indices must be
integers, not str
##################################################################

2

Is there any particular reason why you are doing the “(range(256))”? Keep in mind that a colormap in matplotlib works differently than a colormap in Matlab. In Matlab, the colormap is a 2-D array of rgb values, while in matplotlib, it is an object that is used by the backends for color-rendering.

Often times, you will not need to do anything more than specify which colormap you want by name e.g., pcolor(X, Y, Z, cmap=‘gist_rainbow’), or by passing in a customized or self-made colormap object to the ‘cmap’ keyword argument.

What is happening in your code when you call ‘(range(256))’ is that the colormap is being called for an array of values ranging from 0 to 255 and is determining what the color will be for each of those values. What seems to be happening with those few colormaps is that the call is being made before those maps are properly self-initialized. So, there might be some sort of flaw here that you have exposed, but I would suggest taking another look at what you are trying to accomplish to see if there is a better way.

Thanks for giving matplotlib a try and I hope you continue to use it for your work!

Ben Root

···

On Sun, Oct 17, 2010 at 5:35 PM, braingateway <braingateway@…287…> wrote:

Hi Everyone,

I am trying the matplotlib. I have to say this is a powerful package for

scientific 2-D plotting. However, I encountered some problems when try

to generate several colormaps.

for example:

a=cm.get_cmap(‘gist_rainbow’,256)(range(256))

will give a error:

Traceback (most recent call last):

File “<pyshell#82>”, line 1, in

a=cm.get_cmap(‘gist_rainbow’,256)(range(256))

File “…\site-packages\matplotlib\colors.py”, line 498, in call

if not self._isinit: self._init()

File “…\site-packages\matplotlib\colors.py”, line 649, in _init

self._segmentdata[‘red’], self._gamma)

TypeError: tuple indices must be integers, not str

but other colormaps can actually work:

a=cm.get_cmap(‘gist_stern’,256)(range(256))

a

array([[ 0. , 0. , 0. , 1. ],

[ 0.0716923 , 0.00392157, 0.00784314, 1. ],

[ 0.14338459, 0.00784314, 0.01568627, 1. ],

…,

[ 0.99215686, 0.99215686, 0.97040326, 1. ],

[ 0.99607843, 0.99607843, 0.98520163, 1. ],

[ 1. , 1. , 1. , 1. ]])

I tried all possible colormaps and found out: gist_rainbow, terrain,

bwr, brg, and seismic will generate the same error, all other colormaps

are OK. I wonder is this a bug or expected behavior?

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

##matplotlib verison : ‘1.0.svn’

maps=[m for m in cm.datad if not m.endswith(“_r”)]

for i in maps:

try:

a=cm.get_cmap(i,256)(range(256))

except:

(type, value, traceback) = sys.exc_info()

print “Problems to create %s” % (i,)

print “The error was → %s: %s” % (type, value)

Problems to create gist_rainbow

The error was → <type ‘exceptions.TypeError’>: tuple indices must be

integers, not str

Problems to create terrain

The error was → <type ‘exceptions.TypeError’>: tuple indices must be

integers, not str

Problems to create bwr

The error was → <type ‘exceptions.TypeError’>: tuple indices must be

integers, not str

Problems to create brg

The error was → <type ‘exceptions.TypeError’>: tuple indices must be

integers, not str

Problems to create seismic

The error was → <type ‘exceptions.TypeError’>: tuple indices must be

integers, not str

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

3

Hi Ben,
Thanks a lot for answering my question! I am a newbie to matplotlib,
so please forgive me, if the question is stupid ;p
In my program I wanna know the exact RGBA value of a data point in the
figure, in order to plot a corresponding line with the same color in
another figure. That is why I need to call a(z) to get RGBA value of a
point at (x,y,z) (z is represented by color). If I understood it
correctly, you said I do not need to specify the 'lut' in
cm.get_cmap(name,lut)? I thought the colormap object is actually a
lookup table with a length specified by lut. It turns out I do not
need to specify anything here. But if I do not specify anything the
colormap.N is always 256. What will happen then, if I need more color
steps? I do notice a(2) and a(2.2) returns different values. So I am
very confused about the principle how the RGBA value is generated by
the colormaps.

LittleBigBrain

···

On Mon, Oct 18, 2010 at 12:54 AM, Benjamin Root <ben.root@...1304...> wrote:

On Sun, Oct 17, 2010 at 5:35 PM, braingateway <braingateway@...287...> > wrote:

Hi Everyone,

I am trying the matplotlib. I have to say this is a powerful package for
scientific 2-D plotting. However, I encountered some problems when try
to generate several colormaps.

for example:
a=cm.get_cmap('gist_rainbow',256)(range(256))
will give a error:
Traceback (most recent call last):
File "<pyshell#82>", line 1, in <module>
a=cm.get_cmap('gist_rainbow',256)(range(256))
File "...\site-packages\matplotlib\colors.py", line 498, in __call__
if not self._isinit: self._init()
File "...\site-packages\matplotlib\colors.py", line 649, in _init
self._segmentdata['red'], self._gamma)
TypeError: tuple indices must be integers, not str

but other colormaps can actually work:
a=cm.get_cmap('gist_stern',256)(range(256))
>>> a
array([[ 0. , 0. , 0. , 1. ],
[ 0.0716923 , 0.00392157, 0.00784314, 1. ],
[ 0.14338459, 0.00784314, 0.01568627, 1. ],
...,
[ 0.99215686, 0.99215686, 0.97040326, 1. ],
[ 0.99607843, 0.99607843, 0.98520163, 1. ],
[ 1. , 1. , 1. , 1. ]])

I tried all possible colormaps and found out: gist_rainbow, terrain,
bwr, brg, and seismic will generate the same error, all other colormaps
are OK. I wonder is this a bug or expected behavior?
###############################
##matplotlib verison : '1.0.svn'
>>> maps=[m for m in cm.datad if not m.endswith("_r")]
>>> for i in maps:
try:
a=cm.get_cmap(i,256)(range(256))
except:
(type, value, traceback) = sys.exc_info()
print "Problems to create %s" % (i,)
print "The error was --> %s: %s" % (type, value)

Problems to create gist_rainbow
The error was --> <type 'exceptions.TypeError'>: tuple indices must be
integers, not str
Problems to create terrain
The error was --> <type 'exceptions.TypeError'>: tuple indices must be
integers, not str
Problems to create bwr
The error was --> <type 'exceptions.TypeError'>: tuple indices must be
integers, not str
Problems to create brg
The error was --> <type 'exceptions.TypeError'>: tuple indices must be
integers, not str
Problems to create seismic
The error was --> <type 'exceptions.TypeError'>: tuple indices must be
integers, not str
##################################################################

Is there any particular reason why you are doing the "(range(256))"? Keep
in mind that a colormap in matplotlib works differently than a colormap in
Matlab. In Matlab, the colormap is a 2-D array of rgb values, while in
matplotlib, it is an object that is used by the backends for
color-rendering.

Often times, you will not need to do anything more than specify which
colormap you want by name e.g., pcolor(X, Y, Z, cmap='gist_rainbow'), or by
passing in a customized or self-made colormap object to the 'cmap' keyword
argument.

What is happening in your code when you call '(range(256))' is that the
colormap is being called for an array of values ranging from 0 to 255 and
is determining what the color will be for each of those values. What seems
to be happening with those few colormaps is that the call is being made
before those maps are properly self-initialized. So, there might be some
sort of flaw here that you have exposed, but I would suggest taking another
look at what you are trying to accomplish to see if there is a better way.

Thanks for giving matplotlib a try and I hope you continue to use it for
your work!

Ben Root

4

2010/10/18 脑关(BrainGateway)生命科学仪器 <braingateway@...287...>:

I tried all possible colormaps and found out: gist_rainbow, terrain,
bwr, brg, and seismic will generate the same error, all other colormaps
are OK. I wonder is this a bug or expected behavior?

Hi Ben,
Thanks a lot for answering my question! I am a newbie to matplotlib,
so please forgive me, if the question is stupid ;p

Questions are never stupid ...

In my program I wanna know the exact RGBA value of a data point in the
figure, in order to plot a corresponding line with the same color in
another figure. That is why I need to call a(z) to get RGBA value of a
point at (x,y,z) (z is represented by color). If I understood it
correctly, you said I do not need to specify the 'lut' in
cm.get_cmap(name,lut)? I thought the colormap object is actually a
lookup table with a length specified by lut.

Kind of, but it's initialised from a linear segmentation dictionary,
so you can get cmaps with a precision you want.

It turns out I do not
need to specify anything here.

Default param is 256.

But if I do not specify anything the
colormap.N is always 256. What will happen then, if I need more color
steps?

cm = get_cmap('...', 1024)

I do notice a(2) and a(2.2) returns different values. So I am
very confused about the principle how the RGBA value is generated by
the colormaps.

It's the "magic" to distinguish between integer (in the LUT range) and
float (in [0.0, 1.0]). 2 gives the LUT entry 2, 2.0 will give the
upper value since it's > 1, as will 2.2 do. Try 0.5, and 0.6, or 0.0
and 0.1.

Actually I cannot reproduce your error on a recently (some weeks ago)
checked-out GitHub repo version of mpl 1.0.0. Please provide
mpl.__version__ so that we check if that's the reason - as simple as
it might be.

MacBook-Pro-Friedrich:Report Friedrich$ python
Python 2.6.5 (r265:79063, Jul 18 2010, 12:14:53)
[GCC 4.2.1 (Apple Inc. build 5659)] on darwin
Type "help", "copyright", "credits" or "license" for more information.

import matplotlib.cm
cm = matplotlib.cm.get_cmap('gist_rainbow')
cm(range(256))

array([[ 1. , 0. , 0.16 , 1. ],
       [ 1. , 0. , 0.13908497, 1. ],
       [ 1. , 0. , 0.11816993, 1. ],
       ...,
       [ 1. , 0. , 0.79262575, 1. ],
       [ 1. , 0. , 0.77131287, 1. ],
       [ 1. , 0. , 0.75 , 1. ]])

print matplotlib.__version__

1.0.0

The attribute of the cm where the error occurs on your machine is set
to a valid value for me. I also cannot find any code path leading to
a wrong initialisation of the attribute. Might be that the data the
cm is init'ed from changed. There is a code path initialising the cm
from a tuple (your attribute was a tuple used like a dict), but this
works too: (terrain is such an example):

cm = matplotlib.cm.get_cmap('terrain')
cm(range(256))

array([[ 0.2 , 0.2 , 0.6 , 1. ],
       [ 0.19477124, 0.21045752, 0.61045752, 1. ],
       [ 0.18954248, 0.22091503, 0.62091503, 1. ],
       ...,
       [ 0.98431373, 0.97992157, 0.97898039, 1. ],
       [ 0.99215686, 0.98996078, 0.9894902 , 1. ],
       [ 1. , 1. , 1. , 1. ]])

Might be that there was 'red' misspelled in gist_rainbow in you mpl
version, this may explain the behaviour if we track it down. Can you
do the following to verify this:

import matplotlib._cm
print matplotlib._cm._gist_stern_data

? Thx,
Friedrich

···

On Mon, Oct 18, 2010 at 12:54 AM, Benjamin Root <ben.root@...1304...> wrote:

On Sun, Oct 17, 2010 at 5:35 PM, braingateway <braingateway@...287...> >> wrote:

5

2010/10/18 Friedrich Romstedt <friedrichromstedt@...287...>:

2010/10/18 脑关(BrainGateway)生命科学仪器 <braingateway@...287...>:

I tried all possible colormaps and found out: gist_rainbow, terrain,
bwr, brg, and seismic will generate the same error, all other colormaps
are OK. I wonder is this a bug or expected behavior?

Hi Ben,
Thanks a lot for answering my question! I am a newbie to matplotlib,
so please forgive me, if the question is stupid ;p

Questions are never stupid ...

In my program I wanna know the exact RGBA value of a data point in the
figure, in order to plot a corresponding line with the same color in
another figure. That is why I need to call a(z) to get RGBA value of a
point at (x,y,z) (z is represented by color). If I understood it
correctly, you said I do not need to specify the 'lut' in
cm.get_cmap(name,lut)? I thought the colormap object is actually a
lookup table with a length specified by lut.

Kind of, but it's initialised from a linear segmentation dictionary,
so you can get cmaps with a precision you want.

It turns out I do not
need to specify anything here.

Default param is 256.

But if I do not specify anything the
colormap.N is always 256. What will happen then, if I need more color
steps?

cm = get_cmap('...', 1024)

I do notice a(2) and a(2.2) returns different values. So I am
very confused about the principle how the RGBA value is generated by
the colormaps.

It's the "magic" to distinguish between integer (in the LUT range) and
float (in [0.0, 1.0]). 2 gives the LUT entry 2, 2.0 will give the
upper value since it's > 1, as will 2.2 do. Try 0.5, and 0.6, or 0.0
and 0.1.

Actually I cannot reproduce your error on a recently (some weeks ago)
checked-out GitHub repo version of mpl 1.0.0. Please provide
mpl.__version__ so that we check if that's the reason - as simple as
it might be.

MacBook-Pro-Friedrich:Report Friedrich$ python
Python 2.6.5 (r265:79063, Jul 18 2010, 12:14:53)
[GCC 4.2.1 (Apple Inc. build 5659)] on darwin
Type "help", "copyright", "credits" or "license" for more information.

import matplotlib.cm
cm = matplotlib.cm.get_cmap('gist_rainbow')
cm(range(256))

array([[ 1. , 0. , 0.16 , 1. ],
[ 1. , 0. , 0.13908497, 1. ],
[ 1. , 0. , 0.11816993, 1. ],
...,
[ 1. , 0. , 0.79262575, 1. ],
[ 1. , 0. , 0.77131287, 1. ],
[ 1. , 0. , 0.75 , 1. ]])

print matplotlib.__version__

1.0.0

The attribute of the cm where the error occurs on your machine is set
to a valid value for me. I also cannot find any code path leading to
a wrong initialisation of the attribute. Might be that the data the
cm is init'ed from changed. There is a code path initialising the cm
from a tuple (your attribute was a tuple used like a dict), but this
works too: (terrain is such an example):

cm = matplotlib.cm.get_cmap('terrain')
cm(range(256))

array([[ 0.2 , 0.2 , 0.6 , 1. ],
[ 0.19477124, 0.21045752, 0.61045752, 1. ],
[ 0.18954248, 0.22091503, 0.62091503, 1. ],
...,
[ 0.98431373, 0.97992157, 0.97898039, 1. ],
[ 0.99215686, 0.98996078, 0.9894902 , 1. ],
[ 1. , 1. , 1. , 1. ]])

Might be that there was 'red' misspelled in gist_rainbow in you mpl
version, this may explain the behaviour if we track it down. Can you
do the following to verify this:

import matplotlib._cm
print matplotlib._cm._gist_stern_data

? Thx,
Friedrich

Thanks a lot for your detailed response!
In previous posts I did give the version: '1.0.svn'. Then I installed
the latest stable version. Here is the version info:

print matplotlib.__version__

1.0.0

However, the error is still there.

You could not reproduce the error in your code, because you did not
specify 'lut' when you call get_cmap
try this:
maps=[m for m in matplotlib.cm.datad if not m.endswith("_r")]
for i in maps:
  try:
    a=matplotlib.cm.get_cmap(i,256)(range(256))
  except:
    (type, value, traceback) = sys.exc_info()
    print "Problems to create %s" % (i,)
    print "The error was --> %s: %s" % (type, value)
u will reproduce the error.

Thanks very much to point out I could actually print the colormap
definition-data.
I printed all of them, and found out the colormaps invoking errors are
all tuples but not dictionaries and all other colormaps are actually
dictionaries.
###Examples without Errors###
###They are all dictionaries###
print matplotlib._cm._gist_stern_data
{'blue': ((0.0, 0.0, 0.0), (0.5, 1.0, 1.0), (0.73499999999999999, 0.0,
0.0), (1.0, 1.0, 1.0)), 'green': ((0, 0, 0), (1, 1, 1)), 'red': ((0.0,
0.0, 0.0), (0.054699999999999999, 1.0, 1.0), (0.25, 0.027, 0.25),
(1.0, 1.0, 1.0))}
print matplotlib._cm._jet_data
{'blue': ((0.0, 0.5, 0.5), (0.11, 1, 1), (0.34000000000000002, 1, 1),
(0.65000000000000002, 0, 0), (1, 0, 0)), 'green': ((0.0, 0, 0),
(0.125, 0, 0), (0.375, 1, 1), (0.64000000000000001, 1, 1),
(0.91000000000000003, 0, 0), (1, 0, 0)), 'red': ((0.0, 0, 0),
(0.34999999999999998, 0, 0), (0.66000000000000003, 1, 1),
(0.89000000000000001, 1, 1), (1, 0.5, 0.5))}
###Colormaps invoking Errors###
###They are all Tuples###
Problems to create gist_rainbow
((0.0, (1.0, 0.0, 0.16)), (0.029999999999999999, (1.0, 0.0, 0.0)),
(0.215, (1.0, 1.0, 0.0)), (0.40000000000000002, (0.0, 1.0, 0.0)),
(0.58599999999999997, (0.0, 1.0, 1.0)), (0.77000000000000002, (0.0,
0.0, 1.0)), (0.95399999999999996, (1.0, 0.0, 1.0)), (1.0, (1.0, 0.0,
0.75)))
The error was --> <type 'exceptions.TypeError'>: tuple indices must be
integers, not str
Problems to create terrain
((0.0, (0.20000000000000001, 0.20000000000000001,
0.59999999999999998)), (0.14999999999999999, (0.0,
0.59999999999999998, 1.0)), (0.25, (0.0, 0.80000000000000004,
0.40000000000000002)), (0.5, (1.0, 1.0, 0.59999999999999998)), (0.75,
(0.5, 0.35999999999999999, 0.33000000000000002)), (1.0, (1.0, 1.0,
1.0)))
The error was --> <type 'exceptions.TypeError'>: tuple indices must be
integers, not str
Problems to create bwr
((0.0, 0.0, 1.0), (1.0, 1.0, 1.0), (1.0, 0.0, 0.0))
The error was --> <type 'exceptions.TypeError'>: tuple indices must be
integers, not str
Problems to create brg
((0.0, 0.0, 1.0), (1.0, 0.0, 0.0), (0.0, 1.0, 0.0))
The error was --> <type 'exceptions.TypeError'>: tuple indices must be
integers, not str
Problems to create seismic
((0.0, 0.0, 0.29999999999999999), (0.0, 0.0, 1.0), (1.0, 1.0, 1.0),
(1.0, 0.0, 0.0), (0.5, 0.0, 0.0))
The error was --> <type 'exceptions.TypeError'>: tuple indices must be
integers, not str

···

On Mon, Oct 18, 2010 at 12:54 AM, Benjamin Root <ben.root@...1304...> wrote:

On Sun, Oct 17, 2010 at 5:35 PM, braingateway <braingateway@...287...> >>> wrote: