[Matplotlib-users] Extending a plot outside of axes

[Einar M. Einarsson]

Hi all.

is it not possible to extend plot outside of a plot area? To  
illustrate what I want
to do take for example the wind barbs example from the matplotlib  
gallery.
(see below)

I only changed line 23 from ax.barbs(X, Y, U, V) to ax.barbs(X, Y, - 
U, -V)

But now we don't see the tail of the barbs in the first subplot.

So Is it possible to let matplotlib plot the tail, without extending  
the axes?

Best Regards
Einar M. Einarsson

'''
Demonstration of wind barb plots
'''
import matplotlib.pyplot as plt
import numpy as np

x = np.linspace(-5, 5, 5)
X,Y = np.meshgrid(x, x)
U, V = 12*X, 12*Y

data = [(-1.5, .5, -6, -6),
 (1, -1, -46, 46),
 (-3, -1, 11, -11),
 (1, 1.5, 80, 80),
 (0.5, 0.25, 25, 15),
 (-1.5, -0.5, -5, 40)]

data = np.array(data, dtype=[('x', np.float32), ('y', np.float32),
 ('u', np.float32), ('v', np.float32)])

#Default parameters, uniform grid
ax = plt.subplot(2,2,1)
ax.barbs(X, Y, -U, -V)

#Arbitrary set of vectors, make them longer and change the pivot point
#(point around which they're rotated) to be the middle
ax = plt.subplot(2,2,2)
ax.barbs(data['x'], data['y'], data['u'], data['v'], length=8,  
pivot='middle')

#Showing colormapping with uniform grid.  Fill the circle for an  
empty barb,
#don't round the values, and change some of the size parameters
ax = plt.subplot(2,2,3)
ax.barbs(X, Y, U, V, np.sqrt(U*U + V*V), fill_empty=True,  
rounding=False,
 sizes=dict(emptybarb=0.25, spacing=0.2, height=0.3))

#Change colors as well as the increments for parts of the barbs
ax = plt.subplot(2,2,4)
ax.barbs(data['x'], data['y'], data['u'], data['v'], flagcolor='r',
 barbcolor=['b','g'], barb_increments=dict(half=10, full=20,  
flag=100),
 flip_barb=True)

plt.show()


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[Matplotlib-users] PNG filesize

[Einar M. Einarsson]

Hi all,

I'm trying to find ways to make the file-size of my PNG images smaller.

When I generate my 660*440px image I get a big 168kb file.
(8bit RGB color model, has  an alpha channel (need that) but no
interlacing scheme)

Here it is:
http://metphys.org/eme/T05.png

I'm using the savefig method of-course.


To see how much I could compress it I used pngcrush (the best tool
according to the interwebs) and got it down to 128kb.

But thats still way to large for my intended use. (plotting results
from an operational weather model, see. www.belgingur.is
We are currently using IDL.)

 From what I've read about PNG files, which is supposed to be rather
compact image format, it seems to me that the most effective way is
to have an indexed color table.

So to cut it short:

Is there any way to save a PNG file with an indexed color table?

Or do you see any other way to shrink the files?


Best regards.
Einar M. Einarsson
www.belgingur.is

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