How to filter out annular data from square matrix

Question

Bhowmik.U 2018-7-7

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/409228-how-to-filter-out-annular-data-from-square-matrix

评论： Bhowmik.U 2018-7-9

采纳的回答： Image Analyst

Have a square matrix...501 by 501...Z=501×501

Need to filter out an annular data 20 to 150 centered at (251,251)

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Answer 1

Image Analyst 2018-7-7

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/409228-how-to-filter-out-annular-data-from-square-matrix#answer_327877

在 MATLAB Online 中打开

See the FAQ for creating a circle:

https://matlab.wikia.com/wiki/FAQ#How_do_I_create_a_circle.3F

Then to get row and column indexes for your matrix, simply round, making sure that x is the second dimension, not the first because arrays are indexes as array(y, x) NOT array(x,y)

rows = round(y);
columns = round(x);
for k = 1 : length(rows)
  Z(rows(k), columns(k)) = 0; % Filter to have whatever value you want them to have.
end

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Bhowmik.U 2018-7-7

编辑：Image Analyst 2018-7-8

在 MATLAB Online 中打开

UU_avg.xls

Thanks a lot Sir, it works like cream! Problem solved

A last help I shall request in this thread

I converted the image to pixel format as in figure. I have a 20x20 matrix of UU_avg (attached Excel file) I am also sharing the code which I use to plot..and the resultant image (png).

*However, the resultant plot (in the same enclosed word file) shows only 2 axes..the other two seems to be non-existent

Is there a way out?*

code:

im=surf(UU_avg,'EdgeColor','none','LineStyle','none');
view(-90,90);
xtick = [0, 2.5, 7.5, 10, 12.5, 17.5, 20];
ytick = [0, 2.5, 7.5, 10, 12.5, 17.5, 20];
xticklabels = {'-150','-100', '-50', '0','50', '100', '150'};
yticklabels ={'-150','-100', '-50', '0','50', '100', '150'};
set(gca, 'XTick', xtick);
set(gca, 'YTick', ytick);
set(gca, 'YTickLabel', yticklabels);
set(gca, 'XTickLabel', xticklabels);
hh=colorbar;
title(hh,'%','FontSize',14,'fontweight','bold');
set(gca,'FontSize', 14,'fontweight','bold');
set(gca,'Linewidth',3);
axis tight;
box on;