mrwthumb.cpp

Sample program to extract a Minolta thumbnail from the makernote

// SPDX-License-Identifier: GPL-2.0-or-later
// Sample program to extract a Minolta thumbnail from the makernote
 
#include <exiv2/exiv2.hpp>
#include <iostream>
 
int main(int argc, char* const argv[]) {
  Exiv2::XmpParser::initialize();
  ::atexit(Exiv2::XmpParser::terminate);
 
  try {
    if (argc != 2) {
      std::cout << "Usage: " << argv[0] << " file\n";
      return EXIT_FAILURE;
    }
 
    auto image = Exiv2::ImageFactory::open(argv[1]);
    image->readMetadata();
 
    Exiv2::ExifData& exifData = image->exifData();
    if (exifData.empty()) {
      std::string error(argv[1]);
      error += ": No Exif data found in the file";
      throw Exiv2::Error(Exiv2::ErrorCode::kerErrorMessage, error);
    }
 
    Exiv2::ExifKey key("Exif.Minolta.ThumbnailOffset");
    auto format = exifData.findKey(key);
 
    if (format != exifData.end()) {
      Exiv2::DataBuf buf = format->dataArea();
 
      // The first byte of the buffer needs to be patched
      buf.write_uint8(0, 0xff);
 
      Exiv2::FileIo file("img_thumb.jpg");
 
      file.open("wb");
      file.write(buf.c_data(), buf.size());
      file.close();
    }
 
    return EXIT_SUCCESS;
  } catch (Exiv2::Error& e) {
    std::cout << "Caught Exiv2 exception '" << e << "'\n";
    return EXIT_FAILURE;
  }
}