Re: [Matplotlib-users] how to save pseudo-colorized images as 8-bit PNG files
Eric Firing wrote: You can post-process the image with something like ImageMagick. Another alternative is to use PIL -- you can grab the matplotlib buffer, make a PIL image out of it, and use PIL to convert to an 8-bit palleted image. For that matter, you could probably bypass MPL, and use numpy to create the 8-bit image you want, and PIL to save it as a PNG. -Chris Thanks much for the helpful information. I will revisit PIL; I tried matplotlib because of other requirements (colorbar, various figure annotations) which did not appear to be readily available in PIL. At this stage, it depends on how important the requirement is to reduce the size of the PNG images. -- jv Try optipng: http://optipng.sourceforge.net/ Here I am running it on a gray-scale image created by mpl; it was generated in such a way that there are only 100 distinct shades of gray. You can see that it reduces the file size by quite a bit, converting it from RGBA to grayscale. This is lossless. For this to work, you have to make sure you have no more than 256 distinct colors--they don't have to be gray. -rw-rw-r-- 1 efiring efiring 8458 2010-07-22 16:26 grayfig.png efir...@manini:~$ optipng grayfig.png OptiPNG 0.6.3: Advanced PNG optimizer. Copyright (C) 2001-2009 Cosmin Truta. ** Processing: grayfig.png 800x600 pixels, 4x8 bits/pixel, RGB+alpha Reducing image to 8 bits/pixel, grayscale Input IDAT size = 8352 bytes Input file size = 8458 bytes Trying: zc = 9 zm = 8 zs = 0 f = 0IDAT size = 3721 zc = 9 zm = 8 zs = 0 f = 5IDAT size = 3301 zc = 9 zm = 8 zs = 1 f = 5IDAT size = 3286 Selecting parameters: zc = 9 zm = 8 zs = 1 f = 5IDAT size = 3286 Output IDAT size = 3286 bytes (5066 bytes decrease) Output file size = 3377 bytes (5081 bytes = 60.07% decrease) efir...@manini:~$ ll grayfig.png -rw-rw-r-- 1 efiring efiring 3377 2010-07-22 16:26 grayfig.png Eric -- Thanks much for this information and also for taking the additional time to try the optipng tool. It is very helpful. Since the above mentioned PNG generation is one step in a near real-time products generation system, I was hoping to avoid the addition of another component (i.e., PNG compression) in the stream, but it appears unavoidable. -- jv -- This SF.net email is sponsored by Sprint What will you do first with EVO, the first 4G phone? Visit sprint.com/first -- http://p.sf.net/sfu/sprint-com-first___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
Re: [Matplotlib-users] how to save pseudo-colorized images as 8-bit PNG files
Christopher Barker wrote: Jim Vickroy wrote: The attachment is a simple script that creates a 2D array of unsigned, 8-bit integers and uses matplotlib to save it as a PNG file. Unfortunately, the PNG file is much larger than expected -- apparently because it is True-Color; on my MS Windows machine, bit depth, for the file, is listed as 32 rather than the expected 8. Can matplotlib be used to accomplish this? If so, could someone direct me to where this is discussed? I don't think so directly. MPL uses a 32 bit image buffer internally, and that's what gets saved out in the PNG. You can post-process the image with something like ImageMagick. Another alternative is to use PIL -- you can grab the matplotlib buffer, make a PIL image out of it, and use PIL to convert to an 8-bit palleted image. For that matter, you could probably bypass MPL, and use numpy to create the 8-bit image you want, and PIL to save it as a PNG. -Chris Thanks much for the helpful information. I will revisit PIL; I tried matplotlib because of other requirements (colorbar, various figure annotations) which did not appear to be readily available in PIL. At this stage, it depends on how important the requirement is to reduce the size of the PNG images. -- jv -- This SF.net email is sponsored by Sprint What will you do first with EVO, the first 4G phone? Visit sprint.com/first -- http://p.sf.net/sfu/sprint-com-first___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
[Matplotlib-users] how to erase items in figures
Hello users,
I wish to repeatedly re-plot labels and contour data on a figure since
redrawing the figure is temporally expensive. The attached script (I
apologize for its length), hopefully, illustrates a simplified version
of what I'm trying to do -- contour temporally-varying data on a map
projection.
I do not understand how to erase the plot label each time the figure is
to be reused. I also do not know how to erase the contour-fill
although, based on the generated PNG files, it does not, for unknown
reasons , appear to be necessary. From some postings, it seems that I
have to employ collections attributes, but I have not been able to find
documentation or examples that illustrate this.
My system:
* matplotlib.__version__: '0.91.2'
* sys.version: '2.5.1 (r251:54863, Apr 18 2007, 08:51:08) [MSC
v.1310 32 bit (Intel)]'
Thanks,
-- jv
'''
PURPOSE
Discover a procedure for eliminating the need to redraw each map projection
from scratch each there is new data to be plotted.
Redrawing each map is time-consuming!
AUTHOR
[EMAIL PROTECTED]
'''
import pylab
from matplotlib.toolkits.basemap import Basemap
import numpy
import os
parameters = dict(projection='merc', llcrnrlon=-180,urcrnrlon=180,
llcrnrlat=-80,urcrnrlat=85, lon_0=100,lat_ts=20, resolution='c')
map= Basemap(**parameters)
map.drawcoastlines()
map.drawmapboundary()
map.drawmeridians(pylab.arange(0,360,30))
map.drawparallels(pylab.arange(-90,90,30))
parameters = dict(num=1, figsize=(8, 8), dpi=80, facecolor='w', edgecolor='k',
frameon=False)
figure = pylab.figure(**parameters)
pylab.title('Figure-reuse Trial')
def render(data):
timestamp, longitudes, latitudes, values = data['timestamp'],
data['longitudes'], data['latitudes'], data['values']
longitudes, latitudes = pylab.meshgrid(longitudes, latitudes)
pylab.figure(num=1) # set current figure
parameters = dict(alpha=1, color='white', fontsize=12, fontweight='heavy',
horizontalalignment='left', verticalalignment='center',
transform=pylab.gca().transAxes)
pylab.text(0.01,0.98, timestamp, **parameters)
x, y = map(longitudes, latitudes)
map.contourf(x, y, values)
filename = os.extsep.join(('Reuse-trial',str(data['timestamp'])[:10],'png'))
pylab.savefig(filename)
##pylab.show()
#~ _restore_(figure) TBD: how to erase current label and contour fill colors
although the latter erasure surprisingly does not seem to be required !
def timeline():
''' a generator for fabricated, planet-wide, data for testing purposes '''
data = dict()
delta_x, delta_y = 1.0, 0.5
data['longitudes'] = numpy.arange(-180.0, 180.0+delta_x, delta_x)
data['latitudes'] = numpy.arange(-90.0, 90.0+delta_y, delta_y)
computations = dict(yesterday=horizontal(data['longitudes'],
data['latitudes']), today=vertical(data['longitudes'], data['latitudes']))
for timestamp,values in computations.items():
data['timestamp'] = timestamp
data['values']= values
yield data
def horizontal(longitudes,latitudes):
data = numpy.empty(shape=(longitudes.size, latitudes.size), dtype=float,
order='C')
for index,longitude in enumerate(longitudes):
data[index] = longitude
return data
def vertical(longitudes,latitudes):
data = numpy.empty(shape=(longitudes.size, latitudes.size), dtype=float,
order='C')
for index,latitude in enumerate(latitudes):
data[:,index] = latitude
return data
for data in timeline():
render(data)
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[Matplotlib-users] IOError: [Errno 2] No such file or directory: 'etopo20data.gz'
Hello, I am a first-time user of matplotlib.
When trying to run the plotmap.py example, the following traceback is
generated:
plotmap.py
Traceback (most recent call last):
File C:\Documents and Settings\jim.vickroy\My
Documents\Projects\High-latitudes D-region\plotmap.py, line 13, in
module
topoin = load('etopo20data.gz')
File C:\Python25\Lib\site-packages\matplotlib\mlab.py, line 1252, in
load
fh = cbook.to_filehandle(fname)
File C:\Python25\Lib\site-packages\matplotlib\cbook.py, line 236, in
to_filehandle
fh = gzip.open(fname, flag)
File C:\Python25\lib\gzip.py, line 49, in open
return GzipFile(filename, mode, compresslevel)
File C:\Python25\lib\gzip.py, line 95, in __init__
fileobj = self.myfileobj = __builtin__.open(filename, mode or 'rb')
IOError: [Errno 2] No such file or directory: 'etopo20data.gz'
How do I obtain this file and where should it reside?
I have downloaded proj446_win32_bin.zip and unzipped it, but I do not
see any such file.
I have also attempted to search this user-group archive for references
to etopo20data.gz but repeatedly get an Unable to connect to Search
Server error so I do not know what I'm doing incorrectly.
I have installed:
- matplotlib-0.91.2.win32-py2.5.exe
- basemap-0.9.9.1.win32-py2.5.exe
- httplib2-0.4.0.zip
for use with Python 2.5.1.
I apologize if this has been previously addressed.
Thanks,
-- jv
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