This is a known issue with the contouring code. It's borrowed from an earlier plotting package called GIST, and assumes that the renderer can not handle compound polygons (for example, donut-shaped, with both an inner and outer edge). So instead, it draws "cuts" that go from the inner to the outer edge. When anti-aliasing is turned on, there is a slight overlap or "drawing twice" along this edge which creates what looks like a line. Unfortunately, this can't be remedied by plotting the contour fills and then plotting the contour edges over top (as is done is contourf_demo.py).
As of matplotlib 0.98.x, matplotlib itself can handle compound paths, so we no longer need the cuts. I've made a few attempts at updating the contouring code to avoid them, but got nowhere. The contouring code is very opaque, almost magical code, and most who've dared to go in have barely made it out alive... ;) That said, a fresh pair of eyes may have what it takes... As for a workaround, you could render your contour as opaque, save that out as an image and read it back in. The code to do that won't be pretty, but it just might work. Cheers, Mike kippertoffee wrote: > Hello, > > I am attempting to overlay a filled contour over a custom image. > > I have managed to get something basic working, but i have encountered a > problem: > > When the contourf plot is set to semi-transparent there are visible lines > joining the bottom of the plot and the filled contour edges. I have attached > an image of the plot. > > http://img232.imageshack.us/my.php?image=spambs6.png spam.png > > The code i have used is below; please bear in mind I am not a programmer, so > if the code seems botched, that's because it is. > > ############################### > > import matplotlib.pyplot as plt > from pylab import * > try: > import Image > except ImportError, exc: > raise SystemExit("PIL must be installed to run this example") > > lena = Image.open('lena.jpg') > dpi = rcParams['figure.dpi'] > figsize = lena.size[0]/dpi, lena.size[1]/dpi > > fig = plt.figure(figsize=figsize) > #fig.patch.set_alpha(0.5) > ax = fig.add_subplot(111) > #ax.patch.set_alpha(0.5) > > ax.imshow(lena, origin='lower') > > ax.contourf(z2,[10,15,20,25,30,35,40,45,50,55,60,65],alpha=0.7) > show() > ############################ > > > Can anyone help me with this problem? > > Thanks for reading, > Pete. > -- Michael Droettboom Science Software Branch Operations and Engineering Division Space Telescope Science Institute Operated by AURA for NASA ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
