使用 jpeglib 从 file.jpg 读取原始压缩缓冲区

Question

我正在寻找代码来打开 file.jpg 并将数据加载到缓冲区中，而无需实际解压缩数据。我需要按原样发送数据。

我发现了一个 code 可以读取图像并将其解压缩。我不知道如何修改代码以获取原始字节而不是解压缩版本。

  struct jpeg_decompress_struct cinfo;
  struct my_error_mgr jerr;
  FILE * infile;        /* source file */
  JSAMPARRAY buffer;        /* Output row buffer */
  int row_stride;       /* physical row width in output buffer */

  if ((infile = fopen(filename, "rb")) == NULL) {
    fprintf(stderr, "can't open %s\n", filename);
    return 0;
  }

  /* Now we can initialize the JPEG decompression object. */
  jpeg_create_decompress(&cinfo);

  /* Step 2: specify data source (eg, a file) */
  jpeg_stdio_src(&cinfo, infile);

  (void) jpeg_read_header(&cinfo, TRUE);

  // Here I want to only get raw bytes
  (void) jpeg_start_decompress(&cinfo);

  row_stride = cinfo.output_width * cinfo.output_components;
  /* Make a one-row-high sample array that will go away when done with image */
  buffer = (*cinfo.mem->alloc_sarray)
        ((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1);

  while (cinfo.output_scanline < cinfo.output_height) {

    (void) jpeg_read_scanlines(&cinfo, buffer, 1);
    /* Assume put_scanline_someplace wants a pointer and sample count. */
    // put_scanline_someplace(buffer[0], row_stride);
  }

  /* Step 7: Finish decompression */

  (void) jpeg_finish_decompress(&cinfo);      

  jpeg_destroy_decompress(&cinfo);

  fclose(infile);

Answer 1

在问题post下交流过后发现，如果我们不关心解压，简单的字节读取就足够了。这是解决问题的代码：

char* data = (char*)malloc(max_w*max_h*3 +100); 

if (data == NULL) {
    printf("Input data must not be NULL.\n");
    return 0;
}

FILE *fp = fopen(filename, "rb"); /* b - binary mode */
if (fp == NULL) {
    printf("Error opening file %s\n", filename);
    return 0;
}

struct stat filestatus;
stat(filename, &filestatus);
size_t data_size = filestatus.st_size;

size_t len = fread(data, 1, data_size , fp);
if (len != data_size) {
    printf("Error reading file %s\n", filename);
    return 0;
}

fclose(fp);
return len;

// free(data) when you are done.

使用 jpeglib 从 file.jpg 读取原始压缩缓冲区

Read raw compressed buffer from file.jpg using jpeglib

c++

jpeg

image-compression

libjpeg