How can I find all values that is over and under the iso-value and then visualize them?

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Apo
Apo 2022-10-5
评论： Image Analyst 2022-10-5
Trying some new things and wanted to do something like this
I've been trying for some time now but the closest i can get is the red circle. I figured I could use find() to find these values and then scatter() to visualize it. But I get errors that x and y is not the same length.
Here's the code:
x=linspace(-2,2,1000);
y=x';
z=exp(-(x.^2+y.^2));
a = find(z>0.2)
hold on
s = contour(x,y,z,[0.2 0.2], 'r')
scatter(z,a)

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回答（1 个）

Image Analyst
Image Analyst 2022-10-5
Try this:
x=linspace(-2,2,1000);
y=x';
z=exp(-(x.^2+y.^2));
subplot(2, 1, 1);
imshow(z, []);
colorbar
% Find elements with z > 0.2
mask = z > 0.2;
% Overlay it on the image
subplot(2, 1, 2);
rgbImage = imoverlay(z, mask, 'r');
imshow(rgbImage);
% Get boundaries and display over the original image.
subplot(2, 1, 1);
hold on;
b = bwboundaries(mask);
visboundaries(b);
  2 个评论
Image Analyst
Image Analyst 2022-10-5
Ran in:
But you have far too many points. You have a thousand x locations and a thousand y locations, so that's a million points. If you plotted them all as dots, they would be so close together that it would look essentially like an image. If you want far, far fewer points, like 30, you can do this:
x=linspace(-2,2,30);
y=x';
[X, Y] = meshgrid(x, y)
X = 30×30
-2.0000 -1.8621 -1.7241 -1.5862 -1.4483 -1.3103 -1.1724 -1.0345 -0.8966 -0.7586 -0.6207 -0.4828 -0.3448 -0.2069 -0.0690 0.0690 0.2069 0.3448 0.4828 0.6207 0.7586 0.8966 1.0345 1.1724 1.3103 1.4483 1.5862 1.7241 1.8621 2.0000 -2.0000 -1.8621 -1.7241 -1.5862 -1.4483 -1.3103 -1.1724 -1.0345 -0.8966 -0.7586 -0.6207 -0.4828 -0.3448 -0.2069 -0.0690 0.0690 0.2069 0.3448 0.4828 0.6207 0.7586 0.8966 1.0345 1.1724 1.3103 1.4483 1.5862 1.7241 1.8621 2.0000 -2.0000 -1.8621 -1.7241 -1.5862 -1.4483 -1.3103 -1.1724 -1.0345 -0.8966 -0.7586 -0.6207 -0.4828 -0.3448 -0.2069 -0.0690 0.0690 0.2069 0.3448 0.4828 0.6207 0.7586 0.8966 1.0345 1.1724 1.3103 1.4483 1.5862 1.7241 1.8621 2.0000 -2.0000 -1.8621 -1.7241 -1.5862 -1.4483 -1.3103 -1.1724 -1.0345 -0.8966 -0.7586 -0.6207 -0.4828 -0.3448 -0.2069 -0.0690 0.0690 0.2069 0.3448 0.4828 0.6207 0.7586 0.8966 1.0345 1.1724 1.3103 1.4483 1.5862 1.7241 1.8621 2.0000 -2.0000 -1.8621 -1.7241 -1.5862 -1.4483 -1.3103 -1.1724 -1.0345 -0.8966 -0.7586 -0.6207 -0.4828 -0.3448 -0.2069 -0.0690 0.0690 0.2069 0.3448 0.4828 0.6207 0.7586 0.8966 1.0345 1.1724 1.3103 1.4483 1.5862 1.7241 1.8621 2.0000 -2.0000 -1.8621 -1.7241 -1.5862 -1.4483 -1.3103 -1.1724 -1.0345 -0.8966 -0.7586 -0.6207 -0.4828 -0.3448 -0.2069 -0.0690 0.0690 0.2069 0.3448 0.4828 0.6207 0.7586 0.8966 1.0345 1.1724 1.3103 1.4483 1.5862 1.7241 1.8621 2.0000 -2.0000 -1.8621 -1.7241 -1.5862 -1.4483 -1.3103 -1.1724 -1.0345 -0.8966 -0.7586 -0.6207 -0.4828 -0.3448 -0.2069 -0.0690 0.0690 0.2069 0.3448 0.4828 0.6207 0.7586 0.8966 1.0345 1.1724 1.3103 1.4483 1.5862 1.7241 1.8621 2.0000 -2.0000 -1.8621 -1.7241 -1.5862 -1.4483 -1.3103 -1.1724 -1.0345 -0.8966 -0.7586 -0.6207 -0.4828 -0.3448 -0.2069 -0.0690 0.0690 0.2069 0.3448 0.4828 0.6207 0.7586 0.8966 1.0345 1.1724 1.3103 1.4483 1.5862 1.7241 1.8621 2.0000 -2.0000 -1.8621 -1.7241 -1.5862 -1.4483 -1.3103 -1.1724 -1.0345 -0.8966 -0.7586 -0.6207 -0.4828 -0.3448 -0.2069 -0.0690 0.0690 0.2069 0.3448 0.4828 0.6207 0.7586 0.8966 1.0345 1.1724 1.3103 1.4483 1.5862 1.7241 1.8621 2.0000 -2.0000 -1.8621 -1.7241 -1.5862 -1.4483 -1.3103 -1.1724 -1.0345 -0.8966 -0.7586 -0.6207 -0.4828 -0.3448 -0.2069 -0.0690 0.0690 0.2069 0.3448 0.4828 0.6207 0.7586 0.8966 1.0345 1.1724 1.3103 1.4483 1.5862 1.7241 1.8621 2.0000
Y = 30×30
-2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -2.0000 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.8621 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.7241 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.5862 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.4483 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.3103 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.1724 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -1.0345 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.8966 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586 -0.7586
X = X(:); % Turn into a column vector.
Y = Y(:); % Turn into a column vector.
z=exp(-(X .^ 2 + Y .^ 2));
% subplot(2, 1, 1);
scatter(X, Y);
% colorbar
% Find elements with z > 0.2
Z = reshape(z, length(x), length(y))
Z = 30×30
0.0003 0.0006 0.0009 0.0015 0.0022 0.0033 0.0046 0.0063 0.0082 0.0103 0.0125 0.0145 0.0163 0.0175 0.0182 0.0182 0.0175 0.0163 0.0145 0.0125 0.0103 0.0082 0.0063 0.0046 0.0033 0.0022 0.0015 0.0009 0.0006 0.0003 0.0006 0.0010 0.0016 0.0025 0.0038 0.0056 0.0079 0.0107 0.0140 0.0175 0.0212 0.0247 0.0277 0.0299 0.0311 0.0311 0.0299 0.0277 0.0247 0.0212 0.0175 0.0140 0.0107 0.0079 0.0056 0.0038 0.0025 0.0016 0.0010 0.0006 0.0009 0.0016 0.0026 0.0041 0.0063 0.0092 0.0129 0.0175 0.0229 0.0288 0.0348 0.0405 0.0454 0.0490 0.0509 0.0509 0.0490 0.0454 0.0405 0.0348 0.0288 0.0229 0.0175 0.0129 0.0092 0.0063 0.0041 0.0026 0.0016 0.0009 0.0015 0.0025 0.0041 0.0065 0.0099 0.0145 0.0204 0.0277 0.0362 0.0454 0.0550 0.0640 0.0717 0.0774 0.0804 0.0804 0.0774 0.0717 0.0640 0.0550 0.0454 0.0362 0.0277 0.0204 0.0145 0.0099 0.0065 0.0041 0.0025 0.0015 0.0022 0.0038 0.0063 0.0099 0.0151 0.0220 0.0311 0.0421 0.0550 0.0690 0.0835 0.0972 0.1090 0.1176 0.1222 0.1222 0.1176 0.1090 0.0972 0.0835 0.0690 0.0550 0.0421 0.0311 0.0220 0.0151 0.0099 0.0063 0.0038 0.0022 0.0033 0.0056 0.0092 0.0145 0.0220 0.0323 0.0454 0.0616 0.0804 0.1010 0.1222 0.1423 0.1595 0.1721 0.1788 0.1788 0.1721 0.1595 0.1423 0.1222 0.1010 0.0804 0.0616 0.0454 0.0323 0.0220 0.0145 0.0092 0.0056 0.0033 0.0046 0.0079 0.0129 0.0204 0.0311 0.0454 0.0640 0.0868 0.1132 0.1423 0.1721 0.2004 0.2246 0.2424 0.2518 0.2518 0.2424 0.2246 0.2004 0.1721 0.1423 0.1132 0.0868 0.0640 0.0454 0.0311 0.0204 0.0129 0.0079 0.0046 0.0063 0.0107 0.0175 0.0277 0.0421 0.0616 0.0868 0.1176 0.1535 0.1929 0.2333 0.2717 0.3045 0.3286 0.3413 0.3413 0.3286 0.3045 0.2717 0.2333 0.1929 0.1535 0.1176 0.0868 0.0616 0.0421 0.0277 0.0175 0.0107 0.0063 0.0082 0.0140 0.0229 0.0362 0.0550 0.0804 0.1132 0.1535 0.2004 0.2518 0.3045 0.3546 0.3974 0.4289 0.4455 0.4455 0.4289 0.3974 0.3546 0.3045 0.2518 0.2004 0.1535 0.1132 0.0804 0.0550 0.0362 0.0229 0.0140 0.0082 0.0103 0.0175 0.0288 0.0454 0.0690 0.1010 0.1423 0.1929 0.2518 0.3163 0.3826 0.4455 0.4994 0.5389 0.5598 0.5598 0.5389 0.4994 0.4455 0.3826 0.3163 0.2518 0.1929 0.1423 0.1010 0.0690 0.0454 0.0288 0.0175 0.0103
mask = Z > 0.2;
% Overlay it on the image
hold on;
scatter(X(mask), Y(mask), 'r', 'filled');

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