Hi,
I am working on a PyQt4 application with some embedded MPL figures, and am
also trying to save some figures as png's without displaying them. I am
observing huge memory increases (10s or 100s of Mb) the moment I try to save
a png. I reproduced the issue by combining two mpl examples,
http://matplotlib.sourceforge.net/examples/user_interfaces/embedding_in_qt4.htmland
http://matplotlib.sourceforge.net/examples/api/agg_oo.html. Full code is
attached. When pressing the "save figure" button, memory usage shoots up,
multiple clicks keep sending it higher (although not monotonically).
I tested on two different platforms
- Matplotlib 98.5.2 and Python 2.6.2 on Ubuntu.
- latest Enthought Python Distribution on Windows XP.
The function that does the png saving is:
def save_png():
"""Save an image as a png file"""
pngpath = 'test_mplsave.png'
fig = Figure()
canvas = FigureCanvas(fig)
ax = fig.add_subplot(111)
x = arange(5e3)
ax.plot(x, sin(x))
canvas.print_figure(pngpath)
## tried all things commented out below, all makes no difference ##
#fig.savefig(pngpath)
#del(fig)
#del(canvas)
#del(ax)
#import matplotlib.pyplot as plt
#plt.close(fig)
#import gc
#gc.collect()
Commenting out the canvas.print_figure line fixes the issue.
Am I doing something obviously wrong, or mixing two incompatible ways of
doing things?
Cheers,
Ralf
#!/usr/bin/env python
# embedding_in_qt4.py --- Simple Qt4 application embedding matplotlib canvases
#
# Copyright (C) 2005 Florent Rougon
# 2006 Darren Dale
#
# This file is an example program for matplotlib. It may be used and
# modified with no restriction; raw copies as well as modified versions
# may be distributed without limitation.
import sys, os, random
from PyQt4 import QtGui, QtCore
from numpy import arange, sin, pi
from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.figure import Figure
class MyMplCanvas(FigureCanvas):
"""Ultimately, this is a QWidget (as well as a FigureCanvasAgg, etc.)."""
def __init__(self, parent=None, width=5, height=4, dpi=100):
fig = Figure(figsize=(width, height), dpi=dpi)
self.axes = fig.add_subplot(111)
# We want the axes cleared every time plot() is called
self.axes.hold(False)
self.compute_initial_figure()
FigureCanvas.__init__(self, fig)
self.setParent(parent)
FigureCanvas.setSizePolicy(self,
QtGui.QSizePolicy.Expanding,
QtGui.QSizePolicy.Expanding)
FigureCanvas.updateGeometry(self)
def compute_initial_figure(self):
pass
class MyStaticMplCanvas(MyMplCanvas):
"""Simple canvas with a sine plot."""
def compute_initial_figure(self):
t = arange(0.0, 3.0, 0.01)
s = sin(2*pi*t)
self.axes.plot(t, s)
def save_png():
"""Save an image as a png file"""
pngpath = 'test_mplsave.png'
fig = Figure()
canvas = FigureCanvas(fig)
ax = fig.add_subplot(111)
x = arange(5e3)
ax.plot(x, sin(x))
#canvas.print_figure(pngpath)
## tried all things commented out below, all makes no difference ##
#fig.savefig(pngpath)
#del(fig)
#del(canvas)
#del(ax)
#import matplotlib.pyplot as plt
#plt.close(fig)
#import gc
#gc.collect()
class ApplicationWindow(QtGui.QMainWindow):
def __init__(self):
QtGui.QMainWindow.__init__(self)
self.setAttribute(QtCore.Qt.WA_DeleteOnClose)
self.setWindowTitle("application main window")
self.file_menu = QtGui.QMenu('&File', self)
self.file_menu.addAction('&Quit', self.fileQuit,
QtCore.Qt.CTRL + QtCore.Qt.Key_Q)
self.menuBar().addMenu(self.file_menu)
self.help_menu = QtGui.QMenu('&Help', self)
self.main_widget = QtGui.QWidget(self)
l = QtGui.QVBoxLayout(self.main_widget)
sc = MyStaticMplCanvas(self.main_widget, width=5, height=4, dpi=100)
dc = QtGui.QPushButton('Save image')
l.addWidget(sc)
l.addWidget(dc)
self.main_widget.setFocus()
self.setCentralWidget(self.main_widget)
self.statusBar().showMessage("All hail matplotlib!", 2000)
self.connect(dc, QtCore.SIGNAL("clicked()"), save_png)
def fileQuit(self):
self.close()
def closeEvent(self, ce):
self.fileQuit()
qApp = QtGui.QApplication(sys.argv)
aw = ApplicationWindow()
aw.setWindowTitle("Try saving a simple png image")
aw.show()
sys.exit(qApp.exec_())
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