如何从图像中裁剪出检测到的对象（圆圈）并存储它？

Question

下面的代码使用bwboundaries根据对象的圆度对对象进行分类。

它估计每个物体的面积和周长，并使用这些结果形成一个简单的指标，指示物体的圆度，指标如下：

metric = 4*pi*area/perimeter^2

此度量仅对于圆形等于 1，对于任何其他形状都小于 1。但是在这段代码中，我使用了 0.80 的阈值，这样只有度量值大于 0.80 的对象才会被归类为圆形。

我的问题是，当给定对象归类为圆形时，如何从原始图像img（不是I 或bw）中将其裁剪并保存为新图像？

我认为使用标签矩阵和边界矩阵就足够了，但仍然不知道如何操作它们。

img=imread('cap.png');
I = rgb2gray(img);

% Step 2: Threshold the Image
bw1 = imbinarize(I);
bw = imcomplement(bw1);

% Step 3: Remove the Noise
bw = bwareaopen(bw,30);      % remove small objects
bw = imfill(bw,'holes');    


% Step 4: Find the Boundaries
[B,L] = bwboundaries(bw,'noholes');
imshow(label2rgb(L,@jet,[.5 .5 .5]))
hold on
for k = 1:length(B)
  boundary = B{k};
  plot(boundary(:,2),boundary(:,1),'w','LineWidth',2)
end



% Step 5: Determine which Objects are Round
stats = regionprops(L,'Area','Centroid');
threshold = 0.80;
% loop over the boundaries
for k = 1:length(B)

  % obtain (X,Y) boundary coordinates corresponding to label 'k'
  boundary = B{k};

  % compute a simple estimate of the object's perimeter
  delta_sq = diff(boundary).^2;    
  perimeter = sum(sqrt(sum(delta_sq,2)));

  % obtain the area calculation corresponding to label 'k'
  area = stats(k).Area;

  % compute the roundness metric
  metric = 4*pi*area/perimeter^2;

  % display the results
  metric_string = sprintf('%2.2f',metric);

  % Test if the current object classified as a round
  if metric > threshold
    % HERE, I want to crop the current object from the 'img' 
    % and save it as a new image 
  end

end

title(['Metrics closer to 1 indicate that ',...
       'the object is approximately round'])

Answer 1

您还可以将BoundingBox 属性添加到regionprops，这将有效地限制blob 在边界框内的延伸位置，您可以使用它们来裁剪图像并保存它。它将具有[x y width height] 的形式，其中x 和y 是边界框的左上角坐标，width 和height 当然是宽度和高度。 x 是列坐标，y 是行坐标。您可以使用imcrop 最终裁剪出图像。

img=imread('cap.png');
I = rgb2gray(img);

% Step 2: Threshold the Image
bw1 = imbinarize(I);
bw = imcomplement(bw1);

% Step 3: Remove the Noise
bw = bwareaopen(bw,30);      % remove small objects
bw = imfill(bw,'holes');    


% Step 4: Find the Boundaries
[B,L] = bwboundaries(bw,'noholes');
imshow(label2rgb(L,@jet,[.5 .5 .5]))
hold on
for k = 1:length(B)
  boundary = B{k};
  plot(boundary(:,2),boundary(:,1),'w','LineWidth',2)
end



% Step 5: Determine which Objects are Round
stats = regionprops(L,'Area','Centroid','BoundingBox'); % Change
threshold = 0.80;
% loop over the boundaries
for k = 1:length(B)

  % obtain (X,Y) boundary coordinates corresponding to label 'k'
  boundary = B{k};

  % compute a simple estimate of the object's perimeter
  delta_sq = diff(boundary).^2;    
  perimeter = sum(sqrt(sum(delta_sq,2)));

  % obtain the area calculation corresponding to label 'k'
  area = stats(k).Area;

  % compute the roundness metric
  metric = 4*pi*area/perimeter^2;

  % display the results
  metric_string = sprintf('%2.2f',metric);

  % Test if the current object classified as a round
  if metric > threshold
    % HERE, I want to crop the current object from the 'img' 
    % and save it as a new image 

    % New - crop image
    bb = stats(k).BoundingBox;
    img_crop = imcrop(img, bb);

    % New - Save the image
    imwrite(img_crop, sprintf('crop%d.png', k));
  end

end

title(['Metrics closer to 1 indicate that ',...
       'the object is approximately round'])

请注意，我使用imwrite 将裁剪保存到文件中，并根据您正在查看的 blob ID 命名。因此，如果有多个满足条件的 blob 或圆形对象，您将全部保存。