Convert mesh to BW image?

Question

Ivan Shorokhov 2016-3-1

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/270896-convert-mesh-to-bw-image

评论： Image Analyst 2016-3-4

tr.mat

在 MATLAB Online 中打开

Hello everybody,

[Problem]: I want to convert triangulated mesh to bw image.

Original Images:

Code used:

close all; clc; clear all;  
load tr; % attached
triplot(tr.ConnectivityList,tr.Points(:,1),tr.Points(:,2)); grid on;

Wanted Output: I want to convert triangulated mesh to bw image by using ConnectivityList and Points?

Where
% ConnectivityList: list of faces #ConnectivityList x 3
% Points: vertex positions #V x 2

@Image Analyst

@Walter Roberson

I'll vote for all your answers and would gladly appreciate any comments.

Ivan

2 个评论
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Image Analyst 2016-3-1

Nothing is attached. Have you tried passing the coordinates into poly2mask()?

Ivan Shorokhov 2016-3-1

编辑：Ivan Shorokhov 2016-3-1

@Image Analyst Please check again. I will try poly2mask() now.

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Answer 1

Image Analyst 2016-3-1

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/270896-convert-mesh-to-bw-image#answer_211912

在 MATLAB Online 中打开

activecontour_demo.m

Poly2mask() won't work:

s=load('tr.mat')
tr = s.tr
x = tr.Points(:, 1);
y = tr.Points(:, 2);
subplot(1,2, 1);
scatter(x, y);
x = x - min(x) + 1;
y = y - min(y) + 1;
columns = ceil(max(x));
rows = ceil(max(y));
mask = poly2mask(x, y, rows, columns);
subplot(1,2,2);
imshow(mask);

You are going to have to use activecontour(). I don't have time now to make a demo for you with your data, but I've attached my generic demo below as an m-file.

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Ivan Shorokhov 2016-3-4

编辑：Ivan Shorokhov 2016-3-4

@Image Analyst, Elapsed time is 1.574048 seconds. Any ideas how I can speed it up?

Image Analyst 2016-3-4

在 MATLAB Online 中打开

That doesn't even look right. Are you sure you're using the correct triangles?

You can write the edges directly into the mask instead of summing whole images. It only takes .36 seconds:

s=load('tr.mat')
tr = s.tr
x = tr.Points(:, 1);
y = tr.Points(:, 2);
x = x - min(x) + 1;
y = y - min(y) + 1;
columns = ceil(max(x));
rows = ceil(max(y));
F=tr.ConnectivityList;
V = [tr.Points(:,1),tr.Points(:,2)]; 
x = V (:, 1);y = V (:, 2);
x = x(F)';y = y(F)'; nedges = size(x,2);
x = [x; NaN(1,nedges)]; y = [y; NaN(1,nedges)];
x = x(:); y = y(:); % nan separates triangles
x(x<1) = 1;
y(y<1) = 1;
columns = ceil(max(x)); 
rows = ceil(max(y));
mask = false(rows, columns);
tic
% k = 3:4:length(x);
k = 3:4:length(x);
for f = 1:length(k);
%   f
  x1 = x(k(f)-2);
  x2 = x(k(f));
  y1 = y(k(f)-2);
  y2 = y(k(f));
  numPointsAlongLine = 2.5 * sqrt((x2-x1)^2+(y2-y1)^2);
    xLine = linspace(x1, x2, numPointsAlongLine);
    yLine = linspace(y1, y2, numPointsAlongLine);
  % Round to integer rows and columns
  xLine = round(xLine);
  yLine = round(yLine);
  for p = 1 : length(xLine)
    mask(yLine(p), xLine(p)) = true;
%     imshow(mask, []);
  end
%   if mod(f, 500)
%     imshow(mask, []);
%     drawnow;
%   end
end
imshow(mask, []);
toc
% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Get rid of tool bar and pulldown menus that are along top of figure.
set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off')