[Matplotlib-users] problems with contourf & alpha

[Pablo R. <rom...@ho...>]

Im having an issue where contourf is producing visible defects in the shaded contours (within png output) with alpha values that are less then 1.0.

Ive attached two images.
- the first image,contourf_no_alpha.png, shows my contour plot with the alpha value left at its default
(i.e.,alpha is not set, so alpha=1.0).

- the second image, contourf_with_alpha.png, shows the same contoured data, yet with the alpha set to 0.75.
There are vertical lines visible where the contours are apparently being closed/joined?

I added pink contour lines in order to show that these vertical lines are NOT actually part of the contour.

these are the commands that I used:

Z=create_my_data()

...

# image 1 (contourf_no_alpha.png)
cs=m.contourf(X,Y,Z,lev)
cs=m.contour(X,Y,Z,lev,colors='pink'linewidths=1.5)

# image 2 (contourf_with_alpha.png)
cs=m.contourf(X,Y,Z,lev,alpha=0.75)
cs=m.contour(X,Y,Z,lev,colors='pink',linewidths=1.5)

Im running the latest versions of basemap&matplotlib.

How can I remove these vertical defects while still being able to use "semi-transparent" alpha values?

Please help,

Thanks,

P.Romero
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