使用jpeglib进行JPEG压缩字节流 [英] using jpeglib for JPEG compressed byte stream

问题描述

我将JPEG压缩字节流存储在一个名为"Image"的变量中，我想将此字节流转换为RGB.

I have JPEG compressed byte stream stored in a variable called "Image" and I want to convert this byte stream to RGB.

例如:unsigned char * Image;

Eg: unsigned char *Image;

我的问题是:是否可以将图像"传递给jpeg_stdio_src()以获得RGB颜色值?

My question is: Is there any way to pass "Image" to jpeg_stdio_src() to get the RGB color values?

有人可以告诉我如何使用jpeglib库从字节流"Image"中获取RGB吗?

Can anyone tell me how I could use jpeglib library to get RGB from byte stream "Image"?

谢谢

推荐答案

尝试类似的方法.这使用对象currImage来存储结果(此处未声明).

Try something like this. This uses an object currImage to store the results (not declared here).

typedef struct {
  struct jpeg_source_mgr pub;   // public fields

  JOCTET * buffer;              // start of buffer
  boolean start_of_file;        // have we gotten any data yet?
} my_source_mgr;

typedef my_source_mgr * my_src_ptr;

static void jpg_memInitSource(j_decompress_ptr cinfo)
{
  my_src_ptr src = (my_src_ptr) cinfo->src;
  src->start_of_file = true;
}

static boolean jpg_memFillInputBuffer(j_decompress_ptr cinfo)
{
  my_src_ptr src = (my_src_ptr) cinfo->src;
  src->start_of_file = FALSE;
  return TRUE;
}

static void jpg_memSkipInputData(j_decompress_ptr cinfo, long num_bytes)
{
  my_src_ptr src = (my_src_ptr) cinfo->src;
  if (num_bytes > 0) {
    src->pub.next_input_byte += (size_t) num_bytes;
    src->pub.bytes_in_buffer -= (size_t) num_bytes;
  }
}

static void jpg_memTermSource(j_decompress_ptr cinfo)
{
  // no work necessary here
}

void decompressJpeg(uint8 const *compressed, size_t len)
{
  struct jpeg_decompress_struct cinfo;
  struct jpeg_error_mgr         jerr;
  my_src_ptr src;

  // ToDo: change error handling to work with our return codes
  cinfo.err = jpeg_std_error(&jerr);
  jpeg_create_decompress(&cinfo);

  cinfo.src = (struct jpeg_source_mgr *)
    (*cinfo.mem->alloc_small) ((j_common_ptr) &cinfo, JPOOL_PERMANENT,
    sizeof(my_source_mgr));
  src = (my_src_ptr) cinfo.src;
  src->buffer = (JOCTET *)compressed;

  src->pub.init_source = jpg_memInitSource;
  src->pub.fill_input_buffer = jpg_memFillInputBuffer;
  src->pub.skip_input_data = jpg_memSkipInputData;
  src->pub.resync_to_restart = jpeg_resync_to_restart;
  src->pub.term_source = jpg_memTermSource;
  src->pub.bytes_in_buffer = len;
  src->pub.next_input_byte = compressed;

  jpeg_read_header(&cinfo, true);
  jpeg_start_decompress(&cinfo);

  // check: cinfo.out_color_space == JCS_RGB

  currImage.setSize(
    (int)cinfo.output_width, (int)cinfo.output_height));

  size_t w = currImage.getWidth() * 3;
  uint8 *p = (uint8*)currImage.getPixels();
  while (cinfo.output_scanline < cinfo.output_height) {
    jpeg_read_scanlines(&cinfo, &p, 1);
    p += w;
  }

  jpeg_finish_decompress(&cinfo); // Do this even under error conditions
  jpeg_destroy_decompress(&cinfo); // Do this even under error conditions
}

编辑:添加了一些缺少的支持代码.谢谢，Edu Filipe！

Added some of the missing support code. Thanks, Edu Filipe!

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