Using cv::glob for multiple extensions - c++

Question

I'm trying to use cv::glob to find images in a folder system. What I now want is to search for multiple file extensions at once (let's say .jpg and .png). Is there a way to do this?
The opencv documentation on this method doesn't specify the pattern parameter.
At the moment I'm using the ugly and inefficient method of searching for each extension seperately and combining the results. See:
vector<cv::String> imageNames;
vector<string> allowedExtensions = { ".jpg", ".png" };
for (int i = 0; i < allowedExtensions.size(); i++) {
vector<cv::String> imageNamesCurrentExtension;
cv::glob(
inputFolder + "*" + allowedExtensions[i],
imageNamesCurrentExtension,
true
);
imageNames.insert(
imageNames.end(),
imageNamesCurrentExtension.begin(),
imageNamesCurrentExtension.end()
);
}

Answer 1

Open CV or even OS file system API has no build-in way to do that. You can improve your code by eliminating multiple iteration over the folder/folders. For example you can use boost::filesystem::recursive_directory_iterator and some filter function to retrieve all the files in a single iteration.
Here is the sample:
#include <boost/filesystem.hpp>
#include <set>
namespace fs = ::boost::filesystem;
void GetPictures(const fs::path& root, const std::set<string>& exts, vector<fs::path>& result)
{
if(!fs::exists(root) || !fs::is_directory(root))
{
return;
}
fs::recursive_directory_iterator it(root);
fs::recursive_directory_iterator endit;
while(it != endit)
{
if(fs::is_regular_file(*it) && exts.find(it->path().extension()) != exts.end())
{
result.push_back(it->path());
}
++it;
}
}
It's only a sample, you should take care of string casing, error handling, etc.