Matlab：掩饰/创建一个知道其原点的圆形roi，具有一定的半径 [英] Matlab: mask/create a circular roi knowing its origin point with a certain radius

问题描述

只是一个简单的问题。我有一个图像，我已经提取了某个点（特征），我知道每个帧中该点的坐标。

Just a quick question. I've an image and I've extracted a certain point (feature), I know the coordinates of that point in every frame.

说x1和y1。

我需要一个圆形ROI表格，指向图像上我选择的半径。

I need a circular ROI form that point on the image with a radius that I chose.

我尝试了impoly和roipoly - 当我知道图像中的点时，不知道如何使用其中任何一个。

I tried impoly and roipoly - not sure how to use either of these when I know the point in the image.

谢谢

推荐答案

由于您知道ROI中心的坐标以及半径，您可以修改一下@Jonas提供的代码此处以非常有效的方式创建圆形蒙版。

Since you know the coordinates of the center of the ROI along with the radius, you can modify a bit the code provided by @Jonas here to create a circular mask in a quite efficient way.

示例：

clc;clear

Im = imread('coins.png');

[rNum,cNum,~] = size(Im);

%// Define coordinates and radius
x1 = 60;
y1 = 100;
radius = 40;

%// Generate grid with binary mask representing the circle. Credit to Jonas for original code.
[xx,yy] = ndgrid((1:rNum)-y1,(1:cNum)-x1);
mask = (xx.^2 + yy.^2)<radius^2;

%// Mask the original image
Im(mask) = uint8(0);

imshow(Im)

输出：

编辑

如果您只想查看ROI的外边缘以查看中心，请添加一个具有一定容差的逻辑条件对于较小圆的半径。这样的事情：

If you want to see only the outer edge of the ROI to see the center, add a logical condition with some tolerance for the radius of a smaller circle. Something like this:

mask = (xx.^2 + yy.^2)<radius^2 & (xx.^2 + yy.^2)>(radius-tol)^2;

如果 tol 为2，它看起来像这个：

With a tol of 2 it looks like this:

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