沿边缘的图像上的轮廓

Question

如何在由阈值定义但实际上遵循图像边缘而不是默认情况下的轮廓的图像上绘制轮廓？

通过运行以下命令，

a=50;
b=50;
sd=10;
G = gauss2d(a,b,sd,sd);
x = linspace(0,1,b);
y = linspace(5,20,a);
imagesc(x,y,G)
hold on;contour(x,y,G,mean(mean(G))*[1 1],'r','linewidth',3);
pbaspect([1 1 1])
saveas(gcf,'current.png','png')

我得到以下信息，

但我想拥有，

这个question 和他们的答案很接近并且非常有帮助，但仍然有点混乱。我猜有一个几乎内置的解决方案？

Answer 1

我没有找到任何内置解决方案，因此，我将发布我的版本，它不是特别优雅也不是特别高效，但可能对其他人有所帮助。

function contourEdges(x,y,u,varargin)
    %CONTOUREDGES Contour plot following pixel edges.
    %   CONTOUREDGES(X,Y,Z,V) draw a contour line for each
    %   level specified in vector V.  Use CONTOUREDGES(X,Y,Z,[v v]) to 
    %   draw contours for the single level v.
    %   X and Y must be rows (or column) vecors and Z must be a MxN matrix.
    %
    %   Example:
    %       
    %       data = gauss2d(23,37);
    %       x = linspace(0,1,37);
    %       y = linspace(5,20,23);
    %       imagesc(x,y,data)
    %       m = mean(mean(data));        
    %       %To plot only the level m
    %       contourEdges(x,y,data,[m m])
    %       %To plot more levels: contourEdges(x,y,data,[m/2 m 2*m])
if isempty(varargin) || numel(varargin{1}) < 2
    message = ['Automatic selection of levels is not supported yet. A'...
        'simple workaround is to run [~,C] = contour(x,y,Z,{n}) and then'...
        'use C.LevelList as the fourth parameter here.'];
    error(message);
else
    contourLevels = unique(varargin{1});
end
x = [x(1)-(x(2)-x(1)); x(:); x(end)+(x(2)-x(1))];
y = [y(1)-(y(2)-y(1)); y(:); y(end)+(y(2)-y(1))];
edgesx = mean([x(2:end)';x(1:end-1)']);
edgesy = mean([y(2:end)';y(1:end-1)']);
inputExist = find(cellfun(@(x) strcmpi(x, 'linewidth') , varargin));
if isempty(inputExist)
  varargin{end+1} = 'linewidth';
  varargin{end+1} = 3;
end
if length(varargin{2})>4 && isempty(inputExist)
    varargin{end+1} = 'color';
    varargin{end+1} = [1 0 0];
end
ax = gca;
for contIdx=1:length(contourLevels)
    idx = u > contourLevels(contIdx);
    [a,b] = find(idx);
    for i=1:length(a)
            if b(i) == 1
                ax.ColorOrderIndex = 1;
                hold on;plot([edgesx(b(i)) edgesx(b(i))],[edgesy(a(i)) edgesy(a(i)+1)],varargin{2:end});
            end
            if b(i) ~= size(idx,2)
                if isempty(find(a==a(i) & b==(b(i)+1),1))
                    ax.ColorOrderIndex = 1;
                    hold on;plot([edgesx(b(i)+1) edgesx(b(i)+1)],[edgesy(a(i)) edgesy(a(i)+1)],varargin{2:end});
                end
            end
            if b(i) == size(idx,2)
                ax.ColorOrderIndex = 1;
                hold on;plot([edgesx(b(i)+1) edgesx(b(i)+1)],[edgesy(a(i)) edgesy(a(i)+1)],varargin{2:end});
            end
            if b(i) ~= 1
                if isempty(find(a==a(i) & b==(b(i)-1),1))
                    ax.ColorOrderIndex = 1;
                    hold on;plot([edgesx(b(i)) edgesx(b(i))],[edgesy(a(i)) edgesy(a(i)+1)],varargin{2:end});
                end
            end

            if a(i) == 1
                ax.ColorOrderIndex = 1;
                hold on;plot([edgesx(b(i)) edgesx(b(i)+1)],[edgesy(a(i)) edgesy(a(i))],varargin{2:end});
            end
            if a(i) ~= size(idx,1)
                if isempty(find(b==b(i) & a==(a(i)+1),1))
                    ax.ColorOrderIndex = 1;
                    hold on;plot([edgesx(b(i)) edgesx(b(i)+1)] ,[edgesy(a(i)+1) edgesy(a(i)+1)],varargin{2:end});
                end
            end
            if a(i) == size(idx,1)
                ax.ColorOrderIndex = 1;
                hold on;plot([edgesx(b(i)) edgesx(b(i)+1)],[edgesy(a(i)+1) edgesy(a(i)+1)],varargin{2:end});
            end
            if a(i) ~= 1
                if isempty(find(b==b(i) & a==(a(i)-1),1))
                    ax.ColorOrderIndex = 1;
                    hold on;plot([edgesx(b(i)) edgesx(b(i)+1)],[edgesy(a(i)) edgesy(a(i))],varargin{2:end});
                end
            end
    end
end