Drawing rectangles using matrices.

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Anvinder Singh
Anvinder Singh 2016-2-28
评论： Image Analyst 2018-8-1
Hi, I need to draw a figure as shown in the picture using 256x256 matrix. There should be two rectangles and the rest of the matrix values should be zero. Can you please help ?
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sudharsan V
sudharsan V 2018-8-1
how to draw a triangle instead of rectangle?
Image Analyst
Image Analyst 2018-8-1
Use plot() with 3 x values and 3 y values.

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回答（4 个）

Stephen23
Stephen23 2016-2-28
编辑：Stephen23 2016-2-28
You can use MATLAB's array indexing quite effectively for this:
>> X = ones(256,256,3);
>> X(40:140,[40,140],:) = 0;
>> X([40,140],40:140,:) = 0;
and to view the rectangle:
>> image(X)
creates this:
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Guillaume
Guillaume 2016-2-29
My answer is the same as Stephen's but applied to a 2D matrix.
However, I think you should pause and learn the basics of matrix indexing. If you're not able to understand Stephen's or my code you won't go very far.
In matlab's documentation follow the getting started tutorial.
Anvinder Singh
Anvinder Singh 2016-2-29
Guillaume you are right. I thought the rectangle function you defined was independent of the matrix and was it's values just based on the values given to it so it had nothing to do with the matrix (256*256) so got a little confused.

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Guillaume
Guillaume 2016-2-28
Considering your rectangles are aligned with the side of the image, all you have to do is fill two rows and two columns with 1:
function img = drawrectangle(img, xbounds, ybounds)
img(ybounds, xbounds(1):xbounds(2)) = 1;
img(ybounds(1):ybounds(2), xbounds) = 1;
end
And in your case, you use it like this:
img = zeros(256);
img = drawrectangle(img, [40, 140], [60, 80]); %you didn't show the y coordinates for the 1st rectangle
img = drawrectangle(img, [120, 200], [120, 200]);
imshow(img);
Image Analyst
Image Analyst 2016-2-28
If you want them on a graph, with the y increasing upwards, try this:
rectangle('Position', [40,40,100,100]);
hold on;
rectangle('Position', [120,120,80,80]);
axis([0,220, 0,220]);
Note, your rectangles will overlap/intersect given the coordinates you gave despite the fact that your picture incorrectly shows them not overlapping.
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Image Analyst
Image Analyst 2016-2-28
Then do it the way the other two people showed you. If you want to reverse the y axis direction, you can with something like this
set(gca, 'ydir', 'reverse'); % or 'normal'
Anvinder Singh
Anvinder Singh 2016-2-29
how do i set a given points in a row of matrix as 1 ? example- set x coordinate 40 to 120 as 1 etc..

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Anvinder Singh
Anvinder Singh 2016-3-1
The y axis of the graph is still reversed. I have tried axis([0,280, 0,280]); and set(gca, 'ydir', 'reverse'); % or 'normal'

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