libjpeg ver。 6b jpeg_stdio_src vs jpeg_mem_src [英] libjpeg ver. 6b jpeg_stdio_src vs jpeg_mem_src

问题描述

我使用Libjpeg版本6b。在版本8，他们有一个很好的功能，从内存中读出数据 jpeg_mem_src（...），不幸的是。 6b没有这个功能。

I am using Libjpeg version 6b. In version 8 they have a nice function to read data out of the memory called jpeg_mem_src(...), unfortunately ver. 6b does not have this function.

我可以使用什么来直接从内存读取压缩数据？我看到的是从硬盘驱动器读取的 jpeg_stdio_src 。

What can I use to read compressed data directly from memory? All I see is jpeg_stdio_src which reads from the hard drive.

推荐答案

写自己的...

/* 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，而nbytes是该缓冲区的长度。

where buffer is a pointer to the memory chunk containing the compressed jpeg image, and nbytes is the length of that buffer.

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