如何在MATLAB中在图像上绘制圆?

你可以用普通的 PLOT 命令 circular marker point

[x_p,y_p] = find(points);
imshow(im);         %# Display your image
hold on;            %# Add subsequent plots to the image
plot(y_p,x_p,'o');  %# NOTE: x_p and y_p are switched (see note below)!
hold off;           %# Any subsequent plotting will overwrite the image!

还可以调整打印标记的这些其他特性: MarkerEdgeColor , MarkerFaceColor MarkerSize .

如果要保存新图像及其上绘制的标记,可以查看 this answer I gave 有关保存图形中的图像时保持图像尺寸的问题。

注: 使用打印图像数据时 IMSHOW (或 IMAGE 等),行和列的正常解释基本上会发生翻转。通常情况下,数据的第一维度(即行)被认为是位于x轴上的数据,这可能就是您使用 x_p 作为 FIND y轴 ,因此FIND返回的第一个值是 在这种情况下。

This file 由Matlab Central的Wang Zhenhai编写的文件交换实现了这一技巧。

%----------------------------------------------------------------
% H=CIRCLE(CENTER,RADIUS,NOP,STYLE)
% This routine draws a circle with center defined as
% a vector CENTER, radius as a scaler RADIS. NOP is 
% the number of points on the circle. As to STYLE,
% use it the same way as you use the rountine PLOT.
% Since the handle of the object is returned, you
% use routine SET to get the best result.
%
%   Usage Examples,
%
%   circle([1,3],3,1000,':'); 
%   circle([2,4],2,1000,'--');
%
%   Zhenhai Wang <zhenhai@ieee.org>
%   Version 1.00
%   December, 2002
%----------------------------------------------------------------

rectangle 功能。

documentation

通过将“曲率”属性设置为[1]来绘制圆。绘制圆,使其填充点(2,4)和(4,6)之间的矩形区域。Position属性定义包含圆的最小矩形。

pos = [2 4 2 2];
rectangle('Position',pos,'Curvature',[1 1])
axis equal

imshow(im)
hold on
[y, x] = find(points);
for ii=1:length(x)
  pos = [x(ii),y(ii)];
  pos = [pos-0.5,1,1];
  rectangle('position',pos,'curvature',[1 1])
end

与公认的答案相反,这些圆圈将随图像缩放,您可以放大,它们将始终标记整个像素。

嗯,我不得不在这次通话中重新切换:

k = convhull(x,y);
figure;
imshow(image);         %# Display your image
hold on;            %# Add subsequent plots to the image
plot(x,y,'o');  %# NOTE: x_p and y_p are switched (see note below)!
hold off;           %# Any subsequent plotting will overwrite the image!

答复评论:

x和y是使用以下代码创建的:

temp_hull = stats_single_object(k).ConvexHull;
for k2 = 1:length(temp_hull)
   i = i+1;
     [x(i,1)] = temp_hull(k2,1);    
     [y(i,1)] = temp_hull(k2,2);    
 end;

这可能是因为ConvexHull是另一种方式,因此绘图是不同的。或者我犯了一个错误,应该是这样的

[x(i,1)] = temp_hull(k2,2);    
[y(i,1)] = temp_hull(k2,1);

引用:“矩阵的每一行包含多边形一个顶点的x坐标和y坐标。”

我读这篇文章是因为x是第一列,y是第二列。

vision.ShapeInserter System object 可用于在图像上绘制形状。以下是从文档中绘制黄色圆圈的示例:

yellow = uint8([255 255 0]); %// [R G B]; class of yellow must match class of I
shapeInserter = vision.ShapeInserter('Shape','Circles','BorderColor','Custom','CustomBorderColor',yellow);
I = imread('cameraman.tif'); 
circles = int32([30 30 20; 80 80 25]); %// [x1 y1 radius1;x2 y2 radius2]
RGB = repmat(I,[1,1,3]); %// convert I to an RGB image
J = step(shapeInserter, RGB, circles);
imshow(J);

使用MATLAB和图像处理工具箱R2012a或更新版本,您可以使用 viscircles

% Plot 5 circles at random locations
X = rand(5,1);
Y = rand(5,1);
% Keep the radius 0.1 for all of them
R = 0.1*ones(5,1);
% Make them blue
viscircles([X,Y],R,'EdgeColor','b');

另外,请查看 imfindcircles 实现Hough循环变换的函数。这两个函数的联机文档(上面的链接)都有示例,说明如何在图像中查找圆以及如何在图像上显示检测到的圆。

% Read the image into the workspace and display it.
A = imread('coins.png');
imshow(A)

% Find all the circles with radius r such that 15 ≤ r ≤ 30.
[centers, radii, metric] = imfindcircles(A,[15 30]);

% Retain the five strongest circles according to the metric values.
centersStrong5 = centers(1:5,:);
radiiStrong5 = radii(1:5);
metricStrong5 = metric(1:5);

% Draw the five strongest circle perimeters.
viscircles(centersStrong5, radiiStrong5,'EdgeColor','b');

以下是我认为您需要的方法:

[x_p, y_p] = find (points); 

% convert the subscripts to indicies, but transposed into a row vector
a = sub2ind(size(im), x_p, y_p)';

% assign all the values in the image that correspond to the points to a value of zero
im([a]) = 0; 

% show the new image
imshow(im)