Assign values outside a circle in an image to zero

Question

Nilesh 2022-11-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1860688-assign-values-outside-a-circle-in-an-image-to-zero

评论： Nilesh 2022-11-25

Hello everyone,

I have this image generated from a camera, which is a 2048 by 2048 matrix, called meanB. Each cell in the matrix has its own value, but I have to set the values outside the circle, as shown in the diagram to zero.

I know the centre coordinate of the image (1024,1024), and I know the radius of the circle (1024).

Does any one have any suggestion?

Kind regards,

Nilesh

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Answer 1

Image Analyst 2022-11-23

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1860688-assign-values-outside-a-circle-in-an-image-to-zero#answer_1109633

编辑：Image Analyst 2022-11-23

在 MATLAB Online 中打开

That's answered in the FAQ:

https://matlab.fandom.com/wiki/FAQ#How_do_I_create_a_circle?

% Create a logical image of a circle with specified
% diameter, center, and image size.
% First create the image.
imageSizeX = 2048;
imageSizeY = 2048;
[columnsInImage rowsInImage] = meshgrid(1:imageSizeX, 1:imageSizeY);
% Next create the circle in the image.
centerX = 1024;
centerY = 1024;
radius = 1024;
circlePixels = (rowsInImage - centerY).^2 ...
    + (columnsInImage - centerX).^2 <= radius.^2;
% circlePixels is a 2D "logical" array.
% Now, display it.
image(circlePixels) ;
colormap([0 0 0; 1 1 1]);
title('Binary image of a circle');

Now that you have the circle mask, you can use it to blacken outside of the original RGB or gray scale image.

% Mask image by multiplying each channel by the mask.
maskedRgbImage = rgbImage .* cast(~mask, 'like', rgbImage); % R2016b or later. Works for gray scale as well as RGB Color images.