I have a matrix in matlab of the following form:
A=[1 1 1 -1 -1
0 1 0 1 0
0 1 1 1 1
2 2 0 1 2
2 2 2 2 -1]
This matrix represents a map in the plane. Every A(i, j) is a cell in this map. I want to give color to each cell according to its number. So:
If(A(i, j)<=0)
color(A(i, j)) with black
Elseif(A(i, j)==k)
color(A(i, j)) with color k other than black
end
How to do this in matlab? Any suggestions please?
You can define a number of colours that you want using hsv or manually.
hsv(3)
ans =
1 0 0
0 1 0
0 0 1
Then use colormap to specify the color map.
colormap(hsv(3))
and then use imagesc
imagesc(A)
If you want to specify the colour also it is easy:
a = hsv(3)
a(1,:) = 1; % make the first color white
a(3,:) = 0; % make the last color black
a =
1 1 1
0 1 0
0 0 0
colormap(a)
imagesc(A)
Related
In Matlab, I have a matrix M, say:
M=[0 0 2 2 0 0
0 0 2 2 0 3
1 1 2 2 3 3
1 1 0 0 0 0
1 1 0 0 0 0];
with some connected components labeled 1,2 and 3.
I need to discriminate the components (1, 2 and 3) by using different colors (red, green and blue for example). Any help to do this. Thanks in advance
You can use image and colormap. From the documentation of the former,
image(C) displays the data in array C as an image. Each element of C
specifies the color for 1 pixel of the image.
When C is a 2-dimensional m-by-n matrix, the elements of C are used as
indices into the current colormap to determine the color. For 'direct' CDataMapping (the default),
values in C are treated as colormap indices (1-based if double, 0-based
if uint8 or uint16).
Thererfore, you only need to call image(M+1), so that the values start at 1; and then define a suitable colormap. The colormap is a 3-column matrix, where each row defines a color in terms of its R, G, B components.
M = [0 0 2 2 0 0;0 0 2 2 0 3;1 1 2 2 3 3;1 1 0 0 0 0;1 1 0 0 0 0];
imagesc(M+1) % add 1 so that values start at 1, not 0
cmap = [1 1 1; % white
.7 0 0; % dark red
0 .7 0; % dark green
0 0 .7]; % dark blue
colormap(cmap) % set colormap
axis tight % avoid white space around the values
axis equal % aspect ratio 1:1
I want to add legend in a graph G according to different highlighted edges. Is it possible to do it with only one graph G?
Here is a toy example to play with. I have a plot G.
adj =[0 0 1 1 1; % adjacency matrix
1 0 1 0 1;
0 1 0 1 1;
1 1 1 0 1;
0 0 1 0 0]
G = digraph(adj);
I highlighted all edges with 3 colors according to types of edges. 3 types of edges indicate there are 3 different relation between nodes in my case.
This is how I highlighted all edges:
M(:,:,1)=[0 0 1 0 0;1 0 0 0 1;0 0 0 0 0;1 0 0 0 0;0 0 1 0 0];
M(:,:,2)=[0 0 0 1 0; 0 0 1 0 0;0 1 0 0 1;0 0 0 0 0;0 0 0 0 0];
M(:,:,3)=[0 0 0 0 1; 0 0 0 0 0; 0 0 0 1 0;0 1 1 0 1;0 0 0 0 0];
The difficulty in my problem is that I have to remove vertices whose out-degree is less than some integel (say it's 2). Thus I can't plot 3 graphs independently.
rmvNode=find(outdegree(G)<2); % outdegree is the reason why single G is neccesary
adj(rmvNode,:)=[]; adj(:,rmvNode)=[];
M(:,rmvNode,:)=[]; M(rmvNode,:,:)=[];
G=digraph(adj);
Then we can plot it.
for k=1:3 %Looping depending on the third dimension
[r,c]= find(M(:,:,k)); %Finding non-zero elements
s{k}=r; t{k}=c;
end
h=plot(G);
highlight(h,s{1},t{1},'EdgeColor','r');
highlight(h,s{2},t{2},'EdgeColor','g');
highlight(h,s{3},t{3},'EdgeColor','b');
My ideal situation would be a legend like this: assign red edges to label 'type 1', assign blue edges to 'type 2', and assign green ones to 'type 3'. I want something like this:
Once more: I can't plot 3 graphs independently according to 3 pages in M, combine 3 plots together and then add a legend. Because as you can see, outdegree requires a whole graph G as input, it's not viable to divide G into G1, G2 and G3.
One way would be to manipulate the legend function by adding an invisible plot like this:
%put this at the end of your code
hold on; %to retain current plot
ax=plot(NaN,NaN,'r',NaN,NaN,'g',NaN,NaN,'b'); %plotting invisible points of desired colors
legend(ax,'Type 1','Type 2','Type 3'); %adding the legend
which gives:
I'm writing a MATLAB code, I encountered a problem: I have a (2N+1)*(2N+1) matrix for example 7*7. I want to assign coordinate system to it such that the matrix center is the origin of coordinate system. I mean I want to assign (0,0) to row 4 and column 4 of matrix, (1,0) to row 4 and column 5 of matrix and so on. please help me
Thank you in advance
I want to generate a line of ones in all possible directions in a square matrix like this:
0 0 0 0 0 0 0
0 0 0 0 0 0 1
0 0 0 0 0 1 0
0 0 0 1 0 0 0
0 1 0 0 0 0 0
1 0 0 0 0 0 0
0 0 0 0 0 0 0
center of matrix is the origin. this line has 30 degree from horizontal axis.
What you want is a simple mapping from the original matrix counting system to a customized one. Here I have built two cell matrices, representing the coordinates of the elements in the matrix.
Here I have done a simple mapping as follows:
for ii = 1:7
for jj=1:7
D{ii,jj} = C{ii,jj} - [4,4];
end
end
Generally, for matrix of size 2*N+1, you will do the following:
for ii = 1:2*N+1
for jj = 1:2*N+1
D{ii,jj} = C{ii,jj} - [N+1,N+1];
end
end
where C is the original matrix and D is the mapped matrix. After you well-understood what I have done here, you can then replace the for-loops with more efficient functions such as bsxfun.
Good day,
In Matlab I have got a matrix which is very sparse. Now I would like to plot the 'density' of the matrix. Let's say I have a matrix A:
A = [3 0 0
0 2 0
0 0 1];
Now the plot should look something like:
x
x
x
So there should be a dot (or something else) at each location (row, column) in which matrix A has got a nonzero value.
Any ideas?
spy is what you need:
% taken from MatLab documentation
B = bucky;
spy(B)
Consider something like this:
subs = zeros(0,2);
for ind = [find(A)']
[r,c] = ind2sub(size(A), ind);
subs = [subs; [r,c]];
end
scatter(subs(:,2), subs(:,1));
set(gca,'YDir','Reverse')
xlim([1 size(A,2)])
ylim([1 size(A,1)])
Which, for the matrix A:
0 1 0 1 1
0 0 0 0 0
0 1 0 0 0
0 1 0 1 1
0 0 1 1 0
Gives you the following scatter plot:
What about this :
A=[3 0 0; 0 2 0; 0 0 1];
imagesc(A)
Say I have an boundary image in a logical matrix where true means boundary and false means region interior. The image encodes a tessellation of a 2D domain.
I was wondering if there is a compact way in MATLAB to "fix" those pixel neighborhoods where the separation between adjacent regions is only 4-connected and transform them into 8-connected in a manner that preserves the topology of the tessellation.
I believe this can be done with LUTs, but I'm not sure how to proceed. Do I have to, and if so, how do I exactly evaluate all the 3x3 pixel regions where the connectivity is only 4-wise to fill-in the corresponding pixels?
My proposed solution: use BWHITMISS to find the pixels whose neighborhood is at least 4-connected, dilate the result with a rectangular-shaped structuring element to convert those neighborhoods to 8-connected, finally we combine with the original image using logical-OR.
Example:
bw = [
0 0 0 1 0 1 0
0 0 1 1 1 1 1
0 1 1 1 0 1 0
0 0 1 0 1 0 0
0 1 1 0 0 0 0
0 0 1 0 1 1 1
0 0 1 0 0 1 0
];
hm = bwhitmiss(bw, [0 1 0; 1 1 1; 0 1 0]); %# [-1 1 -1; 1 1 1; -1 1 -1]
bw2 = imdilate(hm,ones(3)) | bw;
We can visualize the result:
[r c] = find(hm);
subplot(121), imshow(bw), hold on, plot(c(:),r(:),'o')
subplot(122), imshow(bw2)