如何将EXIF标记放入JPG中,在C++中使用原始jpeg缓冲区？

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：

在您的代码中为JPEG头部添加EXIF数据偏移量

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);
}

为图片添加EXIF信息

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。