如何将 HOG 特征添加到矩阵中（matlab）

Question

提取图像文件夹的HOG特征后，我想将所有这些结果添加到一个矩阵中。我该怎么做？这是我在 matlab 中的代码：

training_female = 'E:\Training Set\Female Images';

% read all images with specified extention, its jpg in our case
filenames = dir(fullfile(training_female, '*.jpg'));

% count total number of photos present in that folder
total_images = numel(filenames);

for n = 1:total_images

% Specify images names with full path and extension    
full_name= fullfile(training_female, filenames(n).name);

% Read images
training_images = imread(full_name);
[featureVector, hogVisualization] = extractHOGFeatures(training_images);
figure (n)

    % Show all images
    imshow(training_images); hold on;                  
    plot(hogVisualization);
end

Answer 1

通过查看 documentation，调用 extractHOGFeatures 计算给定输入图像的 1 x N 矢量。因为计算它的输出大小可能有点麻烦，这还取决于您为 HOG 检测器设置的参数，所以最好先创建一个空矩阵并在每次迭代时动态连接特征。通常为了性能，如果你想在迭代的基础上填充元素，你会预先分配一个矩阵。不这样做会对性能造成轻微的影响，但根据您的情况，这是最适合的。您可能想要调整 HOG 参数，如果我们以动态方式进行调整，则无需确定矩阵的总大小。

所以做这样的事情。我在修改您的代码的地方放置了 %//New 标签：

training_female = 'E:\Training Set\Female Images';

% read all images with specified extention, its jpg in our case
filenames = dir(fullfile(training_female, '*.jpg'));

% count total number of photos present in that folder
total_images = numel(filenames);

featureMatrix = []; %// New - Declare feature matrix

for n = 1:total_images

    % Specify images names with full path and extension    
    full_name= fullfile(training_female, filenames(n).name);

    % Read images
    training_images = imread(full_name);
    [featureVector, hogVisualization] = extractHOGFeatures(training_images);

    %// New - Add feature vector to matrix
    featureMatrix = [featureMatrix; featureVector];
    figure(n);

    % Show all images
    imshow(training_images); hold on;                  
    plot(hogVisualization);
end

featureMatrix 将包含您的 HOG 特征，其中每行代表每张图像。因此，对于特定图像i，您可以通过以下方式确定HOG特征：

feature = featureMatrix(i,:);

警告

我需要指出的是，上面的代码假定您的目录 中的所有图像都具有相同的大小 。如果不是，则每次 HOG 调用的输出向量大小将不同。如果是这种情况，您将需要一个元胞数组来适应不同的大小。

因此，做这样的事情：

training_female = 'E:\Training Set\Female Images';

% read all images with specified extention, its jpg in our case
filenames = dir(fullfile(training_female, '*.jpg'));

% count total number of photos present in that folder
total_images = numel(filenames);

featureMatrix = cell(1,total_images); %// New - Declare feature matrix

for n = 1:total_images

    % Specify images names with full path and extension    
    full_name= fullfile(training_female, filenames(n).name);

    % Read images
    training_images = imread(full_name);
    [featureVector, hogVisualization] = extractHOGFeatures(training_images);

    %// New - Add feature vector to matrix
    featureMatrix{n} = featureVector;
    figure(n);

    % Show all images
    imshow(training_images); hold on;                  
    plot(hogVisualization);
end

要访问特定图像或图像 i 的功能，请执行：

feature = featureMatrix{i};

如何将 HOG 特征添加到矩阵中（matlab）

How to add HOG features into matrix (matlab)

matlab

image-processing

matrix

computer-vision

matlab-cvst

警告