border of random colour around grey image

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Oscar Tsang 2019-3-3

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https://ww2.mathworks.cn/matlabcentral/answers/448010-border-of-random-colour-around-grey-image

编辑： DGM 2022-7-16

owl.jpg

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Hi,

I was wondering how would you put a border of random colour (50 mpixels wide) around the grey image?? Just stuck on how to approach it. I have attached the iamge I have used.

An image in what it suppose to look like:

The code i have done so far:

owl = imread('owl.jpg');
owl_eye=owl;
owl_eye=owl_eye(350:450,600:710,:)
figure
imshow(owl_eye,'InitialMagnification', 'fit');
owleye_gray=rgb2gray(owl_eye);
figure
imshow(owleye_gray,'InitialMagnification', 'fit');

回答（2 个）

Image Analyst 2019-3-3

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Use the color thresholder app on the Apps tab of the tool ribbon to create a mask for the yellow owl eyes. Use hsv color space. Then use bwareafilt() to get only the two eyes

mask = bwareafilt(mask, 2); % Extract 2 largest blobs.

Then use bwconvhull to get the convex hull of them and then use regionprops to get the bounding box:

mask = bwconvhull(mask); % Combine two eyes into one blob.
props = regionprops(mask, 'BoundingBox'); % Get bounding box of the single blob.
hold on;
% Put random colored box in the overlay above the image.
rectangle('Position', props.BoundingBox, 'Color', rand(1, 3)); % Box in random color over image.

Post your code with any problems.

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Image Analyst 2019-3-5

testRGBImage.m

Oscar:

Yes, that's weird. Same for me. Maybe I'll call the Mathworks tomorrow and ask them about it. Meanwhile, my code is attached.

DGM 2022-7-16

The length of padsize defines which dimensions get padded; padarray() does not expand padsize if it's specified as a scalar. As a consequence, only the first dimension will get padded.

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DGM 2022-7-16

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https://ww2.mathworks.cn/matlabcentral/answers/448010-border-of-random-colour-around-grey-image#answer_1008675

编辑：DGM 2022-7-16

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While this answer covers a number of ways to get a border on an image, it also demonstrates that getting a colored border is a bit inconvenient using MATLAB/IPT tools. Considering that, I'm going to use MIMT addborder() as described therein.

A = imread('peppers.png');
bcolor = rand(1,3); % random color
B = addborder(A,10,bcolor,'normalized');

Of course, instead of an entirely random color, you could draw colors randomly from a color table:

A = imread('peppers.png');
cmap = parula(64);
bcolor = cmap(randi([1 size(cmap,1)],1,1),:);
B = addborder(A,10,bcolor,'normalized');

... that would at least keep everything within a specified color scheme:

A = imread('peppers.png');
A = imresize(A,0.5); % don't need a bunch of big images for a demo
cmap = parula(64);
B = cell(4,1);
for f = 1:numel(B)
    bcolor = cmap(randi([1 size(cmap,1)],1,1),:);
    B{f} = addborder(A,5,bcolor,'normalized');
end
montage(B)