Why do image coordinate switches when using getpts function?

Question

Arbol 2017-12-1

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https://ww2.mathworks.cn/matlabcentral/answers/370494-why-do-image-coordinate-switches-when-using-getpts-function

评论： Arbol 2017-12-2

I have a 96x256x256 data, and I try to pick a pixel from the 256x256 to get data. When I use the getpts function, I get different x and y coordinates. Here is my approach to my data: 1. I have data that contain x and y coordinates, and data set(size of 96) at x-y coordinate. 2. I re-edited the data so I can put it into a matrix called tissue_map by doing a for loop:

for i = 1:length(xcoord)
    tissue_map(:,xcoord(i),ycoord(i)) = tissueData(:,i);
end

After this, I use getpts to get a coordinate on one slice of the matrix, say tissue_map(1,120,130):

fig = imagesc(tissue_map(1,:,:));
[x, y] = getpts(fig);
where I get:
x = 130
y = 120

What is it that I'm doing wrong? I couldn't figure out why.

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Answer 1

Walter Roberson 2017-12-1

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I do not see a problem?

In matrix indexing, "up/down" is row indexing, the first index. Up/down corresponds to Y coordinates. So x = 130, y = 120 is row 120 column 130, index (120,130)

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Walter Roberson 2017-12-2

How are you constructing xcoord and ycoord ?

Arbol 2017-12-2

在 MATLAB Online 中打开

1. I have raw data that give x and y coordinate with size of 1x(256*256). Where each row of x increases by 1, each column of y increases by 1. I noticed that this is opposite than MATLAB's indexing. So:

2. I do some data processing to get my region of interest (xvec and yvec) to then put it in:

fit_xcoord = zeros(256,256);
fit_ycoord = zeros(256,256);
fit_intensity = zeros(length(time),256,256);
for i=1:length(xvec)
    IPx = xvec(i); IPy = yvec(i);
    fit_zcoord = zcoord;
    %-- Flip x and y coordinates
    fit_xcoord(IPx,IPy)= ycoord(IPx,IPy); 
    fit_ycoord(IPx,IPy)= xcoord(IPx,IPy);
    fit_intensity(:,IPx,IPy) = intensity_subtracted(:,IPx,IPy);
end

Where I flipped the xvec and yvec in the fit_xcoord and fit_ycoord so the indexing are similar to MATLAB's.

3. I use what I asked above to get my coordinate of interest by using getpts:

for i = 1:length(xcoord)
    tissue_map(:,xcoord(i),ycoord(i)) = tissueData(:,i);
end
fig = imagesc(tissue_map(1,:,:));
[x, y] = getpts(fig);
where I get:
x = 130
y = 120