Aliasing with Makie contourf

General Usage
1

Is there a way to get rid of the aliasing in the contourf! lines in the following example?

using CairoMakie

function testcontourf()
    xs = LinRange(0, 10, 100)
    ys = LinRange(0, 10, 100)
    zs = [cos(x) * sin(y) for x in xs, y in ys]

    f = Figure()
    ax = Axis(f[1, 1])

    c = contourf!(ax, xs, ys, zs, levels = 50)
    Colorbar(f[1, 2], c)
    display(f)
end

testcontourf()

image
image800×600 165 KB

In actuality, I’d prefer to get the plot to look the way it does if I double the contourf! call, and eliminated the lines that show up.

function testcontourf_double()
    xs = LinRange(0, 10, 100)
    ys = LinRange(0, 10, 100)
    zs = [cos(x) * sin(y) for x in xs, y in ys]

    f = Figure()
    ax = Axis(f[1, 1])

    c = contourf!(ax, xs, ys, zs, levels = 50)
    c = contourf!(ax, xs, ys, zs, levels = 50)
    Colorbar(f[1, 2], c)
    
    display(f)
end

testcontourf_double()

Which results in this image without the lines.

image
image800×600 92.7 KB

2

So, you maybe just want a heatmap? there is also the option of interpolate=true, to get smooth interpolation between data points

3

Neat, I didn’t know about the interpolate option for heatmap!. That helps. I’m guessing the lines are just a result of the way Makie plots each level?

4

Well, if you plot lines too closely together they will alias… You would need some global anti aliasing pre-processing filter on top of that, which usually isn’t used in e.g. CairoMakie, which aliases each object (e.g. the lines) separately for optimal quality.

A global aliasing filter is usually not preferred if possible, since it has much less information and introduces new artifacts that way.

5

Ok, that makes sense. Either way, thanks for your work on Makie! It’s my go-to plotting library in julia

1 Like