Contourf: fill inside instead of outside

Question

Marco Sammito 2019-4-7

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https://ww2.mathworks.cn/matlabcentral/answers/454990-contourf-fill-inside-instead-of-outside

评论： DGM about 18 hours 前

Hi, how can I fill the area within the circle? At the moment Matlab fills the area outside. I would like the outside to be white and the inside to be filled. Thanks.

relamdt=-4:0.1:4;
imlamdt=-4:0.1:4;
[x,y]=meshgrid(relamdt,imlamdt);
axis square;
lamdt=x+i*y;
sig = (1 + lamdt);
v = [1,1];
contourf(x,y,abs(sig),v)

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Answer 1

Walter Roberson 2019-4-8

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https://ww2.mathworks.cn/matlabcentral/answers/454990-contourf-fill-inside-instead-of-outside#answer_369653

编辑：Walter Roberson 2019-4-8

在 MATLAB Online 中打开

contourf(x, y, -abs(sig), -v)

Alternately, possibly

[~,h] = contourf(x, y, abs(sig), v);
drawnow();     %seems to be needed to get NodeChildren created
bg = h.NodeChildren(2).ColorData;
h.NodeChildren(2).ColorData = uint8([255; 255; 255; 255]);
ax = ancestor(h,'axes');
ax.Color = bg;

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Answer 2

David Wilson 2019-4-8

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https://ww2.mathworks.cn/matlabcentral/answers/454990-contourf-fill-inside-instead-of-outside#answer_369519

在 MATLAB Online 中打开

A quick hack (following the essence of your code) is

cmap = colormap; cmap(end,:) = [1,1,1]; colormap(cmap); 
contourf(x,y,abs(sig),[0,1]);
axis square

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Marco Sammito 2019-4-8

It does not seem to affect anything. The area within the circle is still white: the outside is still green. I would like to invert these two. Inside=green, outside=white.

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Answer 3

Roberto Tumolo about 18 hours 前

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https://ww2.mathworks.cn/matlabcentral/answers/454990-contourf-fill-inside-instead-of-outside#answer_1491211

What if one wants to extract the values shown inside and outside (suppose you don't know them because they come from a contour?

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DGM about 18 hours 前

The way the question is posed makes it unclear what information we might have. From a contour()/contourf() object, we can know a set of discrete z-values associated with the given level curves, but unless we have access to the original zdata, we don't know the actual values between the level curves. If we don't have access to the object itself (e.g. if all we have is a saved figure as a raster image (a screenshot)), then things get more restricted.

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