libjpeg ver.6b jpeg_stdio_src vs jpeg_mem_src

Question

我正在使用Libjpeg版本6b.在版本8中,他们有一个很好的功能来从内存中读取数据jpeg_mem_src(...),不幸的是ver.6b没有此功能.

我可以用什么来直接从内存中读取压缩数据？我只看到jpeg_stdio_src从硬盘读取的内容.

Answer 1

写你自己的......

/* Read JPEG image from a memory segment */
static void init_source (j_decompress_ptr cinfo) {}
static boolean fill_input_buffer (j_decompress_ptr cinfo)
{
    ERREXIT(cinfo, JERR_INPUT_EMPTY);
return TRUE;
}
static void skip_input_data (j_decompress_ptr cinfo, long num_bytes)
{
    struct jpeg_source_mgr* src = (struct jpeg_source_mgr*) cinfo->src;

    if (num_bytes > 0) {
        src->next_input_byte += (size_t) num_bytes;
        src->bytes_in_buffer -= (size_t) num_bytes;
    }
}
static void term_source (j_decompress_ptr cinfo) {}
static void jpeg_mem_src (j_decompress_ptr cinfo, void* buffer, long nbytes)
{
    struct jpeg_source_mgr* src;

    if (cinfo->src == NULL) {   /* first time for this JPEG object? */
        cinfo->src = (struct jpeg_source_mgr *)
            (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
            SIZEOF(struct jpeg_source_mgr));
    }

    src = (struct jpeg_source_mgr*) cinfo->src;
    src->init_source = init_source;
    src->fill_input_buffer = fill_input_buffer;
    src->skip_input_data = skip_input_data;
    src->resync_to_restart = jpeg_resync_to_restart; /* use default method */
    src->term_source = term_source;
    src->bytes_in_buffer = nbytes;
    src->next_input_byte = (JOCTET*)buffer;
}

然后使用它:

...
    /* Step 2: specify data source (eg, a file) */
    jpeg_mem_src(&dinfo, buffer, nbytes);
...

其中buffer是指向包含压缩jpeg图像的内存块的指针,nbytes是该缓冲区的长度.

Answer 2

回答那些一直在等待答案一年多的穷人s093294.我无法发表评论,因此创建新答案是唯一的方法.

ERREXIT是libjpeg中的一个宏.包括jerror.h,你就完成了.