在C++中,您可以使用标准库中的JPEG格式支持,以及开源库如libjpeg库,将EXIF数据嵌入到JPEG图像中。要在C++中将EXIF标记放入JPG中,首先确保安装了libjpeg库和CMake。下面将提供一个简单的使用示例:
在图像上添加EXIF信息,您需要为JPEG头部添加新的EXIF数据偏移量。默认情况下,JPEG头部偏移量由libjpeg库使用,因此,我们需要为这个偏移量提供一个新值。在C++代码中,可以在jpeg_std_error
结构中定义偏移量值:
#include <jerror.h>
#include "libjpeg/jpeglib.h"
error_code add_exif_tags(unsigned char *jpeg_buffer, int jpeg_buffer_length, const std::string &exif_information) {
// Modify the start offset to add EXIF metadata
unsigned char *new_jpeg_buffer = nullptr;
const int new_jpeg_buffer_length = 0;
j_compress_ptr cinfo = (j_compress_ptr) jpeg_create_decompress(JPEG_LIB_VERSION, new_jpeg_buffer, &new_jpeg_buffer_length);
// Continue modifying the JPEG buffer until a valid return is obtained
// ...
jpeg_destroy_decompress(&cinfo);
return EC_SUCCESS;
}
// usage example
const int exif_tags_size = 128; // Length of the EXIF tags
const std::string exif_information = "Exposure,Aperture,Shutter Speed,ISO"; // EXIF information
const unsigned char exif_bytes[12] = {'\x00', '\x00', '\x81', '\x48', '\x73', '\x4E', '\x00', '\x20', '\x00', '\x00', '\x00'};
// Set the new metadata bytes in the image and save it (e.g., JPEG)
main() {
// Get access to the JPEG file
unsigned char *jpeg_buffer = nullptr;
unsigned char *jpeg_buffer_ptr = nullptr;
int jpeg_buffer_length = 0;
// Open the JPEG file
FILE *file = fopen("image.jpg", "rb");
jpeg_create_decompress(&cinfo); // Create a JPEG decompress context
get_jpeg_memory_buffer(&cinfo, &buffer_length, file);
fclose(file);
// Add the custom Exif bytes
add_exif_tags(buffer_ptr, buffer_length, exif_information.c_str());
// Write modified image to new file
std::string new_image_filename = "new_image.jpg";
int ret = jpeg_save_file(jpeg_buffer, new_jpeg_buffer, exif_tags_size, cinfo, new_image_filename.c_str());
// Continue with any operations you may have on the new image ...
// Clean up
jpeg_destroy_decompress(&cinfo);
get_jpeg_memory_buffer(&cinfo, nullptr, nullptr);
}
接下来,为了将EXIF信息添加到图片,您可以修改应用程序逻辑,以便在获取或写入jpeg数据的特定位置之前或之后添加EXIF数据。例如,您可以在保存jpeg之前将jpeg_buffer中的EXIF数据复制到jpeg_new_buffer中。
这是一个更高级的使用示例,以显示如何将“Exposure,Aperture,Shutter Speed,ISO”格式的EXIF信息添加到图像中。在add_exif_tags()
函数中,将定义新的JPEG头部的偏移量,并将EXIF数据附加到JPEG缓冲区:
error_code add_exif_tags(unsigned char *jpeg_buffer, int len, const std::string &exif_information) {
// Get access to the JPEG file
unsigned char *jpeg_new_buffer = nullptr;
const int new_jpeg_buffer_length = 0;
j_compress_ptr cinfo = (j_compress_ptr) jpeg_create_decompress(JPEG_LIB_VERSION, new_jpeg_buffer, &new_jpeg_buffer_length);
// Continue modifying the JPEG buffer ...
// Add the new header offset (for Exif data) if needed
// Add the custom Exif bytes (Exposure,Aperture,Shutter Speed,ISO)
// Write modified image to new file
// Clean up
jpeg_destroy_decompress(&cinfo);
return EC_SUCCESS;
}
// Get access to the JPEG file
unsigned char *compressed_data = nullptr;
const int compressed_length = 0;
const std::string exif_information = "Exposure,Aperture,Shutter Speed,ISO"; // EXIF information
main() {
// Open the JPEG file
FILE *file = fopen("image.jpg", "r"); // Read mode is required
jpeg_create_decompress(&cinfo); // Create a JPEG decompress context
get_jpeg_memory_buffer(&cinfo, &compressed_length, file); // Read the compressed pixels
fclose(file);
// Modify the image to include the custom metadata (Exif format)
add_exif_tags(compressed_data, compressed_length, exif_information);
// Write the modified image to a new file
}
这个例子中,add_exif_tags()
函数的参数为压缩数据,需要将新的EXIF信息以十六进制格式的bytes添加。您需要根据具体的EXIF数据格式,将新的EXIF标签附加到压缩数据中。
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