如何在图像中获取对象的像素位置

Question

假设我有一个如下所示的二进制图像.我想得到所有矩形形状和圆形形状的位置(X,Y坐标的像素值).如何检测那里有多少个矩形和圆形.我想在Matlab中获得解决方案.矩形和圆形可以具有不同的尺寸.这里的小圆圈是噪音.提前致谢.

Answer 1

你需要:

1. 找到连接的组件(bwconncomp)
2. 找到每个连接组件的一些统计信息(regionprops)
3. 丢弃太小的连接组件,在该区域上定义阈值
4. 查找连接的组件是矩形还是圆/椭圆.您可以使用定义为的圆度4*pi*Area / (Perimeter^2).完美的圆圈将具有值1,正方形0.785等.因此,您可以在圆度上定义阈值,以确定形状是否为圆/椭圆.

这里的结果是删除了较小的blob,以及不同颜色的圆/椭圆和矩形:

码:

% Read image
img = imread('path_to_image');

% Convert to grayscale
img = rgb2gray(img);

% Remove JPEG artifacts
bw = img > 20;

% Prepare output image
output = zeros(size(bw));

% Compute connected components, and their statistics
cc = bwconncomp(bw);
props = regionprops(cc, 'Area', 'Perimeter');

% Will contain x,y coordinates for rectanles and circles
coord_rect = {};
coord_circ = {};

% Define thresholds on size and circularity
th_size = 200;
th_circ = 0.8;

% For each connected component
for i = 1 : cc.NumObjects

    % Is big enough?
    if(props(i).Area < th_size) 
        continue;
    end

    % Rectangle or Circle?
    circularity = 4 * pi * props(i).Area / (props(i).Perimeter ^ 2);
    [y,x] = ind2sub(cc.ImageSize, cc.PixelIdxList{i});

    if(circularity > th_circ)
        % Circle
        output(cc.PixelIdxList{i}) = 1;
        coord_circ{end+1} = [x, y];
    else
        % Rectangle
        output(cc.PixelIdxList{i}) = 2;
        coord_rect{end+1} = [x, y];
    end

end

% Show results
imshow(bw);
figure();
imagesc(output);