1 #!/usr/bin/env python2.4
 2 
 3 """
 4 This is a small demo file that helps teach how to adjust figure sizes
 5 for matplotlib
 6 
 7 First a little introduction:
 8 
 9 There are three parameters define an image size (this is not MPL specific):
 10 
 11 Size in length units (inches, cm, pt, etc): i.e. 5"x7"
 12 Size in pixels: i.e. 800x600 pixels
 13 Dots per inch (dpi) i.e. 100 dpi
 14 
 15 Only two of these are independent, so if you define two of them, the
 16 third can be calculated from the others.
 17 
 18 When displaying on a computer screen (or saved to a PNG), the size in
 19 length units is irrelevant, the pixels are simply displayed. When
 20 printed, or saved to PS, EPS or PDF (all designed to support printing),
 21 then the Size or dpi is used to determine how to scale the image.
 22 
 23 Now I'm getting into how MPL works:
 24 
 25 1) The size of a figure is defined in length units (inches), and can be
 26 set by:
 27 
 28 Figure.set_figsize_inches( (w,h) )
 29 
 30 2) The layout of the figure is defined in 'figure units' so that as the
 31 figure size is changed, the layout (eg axes positions) will update.
 32 
 33 3) Size of text, width of lines, etc is defined in terms of length units
 34 (points?).
 35 
 36 4) When displaying to the screen, or creating an image (PNG) the pixel
 37 size of text and line widths, etc is determined by the dpi setting,
 38 which is set by:
 39 
 40 Figure.set_dpi( val )
 41 
 42 The trick here is that when printing, it's natural to think in terms of
 43 inches, but when creating an image (for a web page, for instance), it is
 44 natural to think in terms of pixel size. However, as of 0.84, pixel size
 45 can only be set directly in the GTK* back-ends, with the
 46 canvas.resize(w,h) method. (remember that you can only set two of the
 47 three size parameters, the third must be calculated from the other
 48 two).
 49 
 50 Another trick:
 51 
 52 Figure.savefig() overrides the ppi setting in figure, and uses a default
 53 (which on my system at least is 100ppi). I you want to overide it, you
 54 can specify the ppi in the savefig call:
 55 
 56 Figure.savefig(filename, ppi=value)
 57 
 58 The following code will hopefully make this more clear, at least for
 59 generating PNGs for web pages and the like.
 60 
 61 """
 62 
 63 import matplotlib
 64 print "using MPL version:", matplotlib.__version__
 65 matplotlib.use("WXAgg") # do this before pylab so you don'tget the default back end.
 66 
 67 import pylab
 68 import matplotlib.numerix as N
 69 
 70 # Generate and plot some simple data:
 71 x = N.arange(0, 2*N.pi, 0.1)
 72 y = N.sin(x)
 73 
 74 pylab.plot(x,y)
 75 F = pylab.gcf()
 76 
 77 # Now check everything with the defaults:
 78 DPI = F.get_dpi()
 79 print "DPI:", DPI
 80 DefaultSize = F.get_size_inches()
 81 print "Default size in Inches", DefaultSize
 82 print "Which should result in a %i x %i Image"%(DPI*DefaultSize[0], DPI*DefaultSize[1])
 83 # the default is 100dpi for savefig:
 84 F.savefig("test1.png")
 85 # this gives me a 797 x 566 pixel image, which is about 100 DPI
 86 
 87 # Now make the image twice as big, while keeping the fonts and all the
 88 # same size
 89 F.set_figsize_inches( (DefaultSize[0]*2, DefaultSize[1]*2) )
 90 Size = F.get_size_inches()
 91 print "Size in Inches", Size
 92 F.savefig("test2.png")
 93 # this results in a 1595x1132 image
 94 
 95 # Now make the image twice as big, making all the fonts and lines
 96 # bigger too.
 97 
 98 F.set_figsize_inches( DefaultSize )# resetthe size
 99 Size = F.get_size_inches()
 100 print "Size in Inches", Size
 101 F.savefig("test3.png", dpi = (200)) # change the dpi
 102 # this also results in a 1595x1132 image, but the fonts are larger.