jpeg2rle发布

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文章出处：http://www.limodev.cn/blog
作者联系方式：李先静 <xianjimli at hotmail dot com>

jpeg2rle发布

RLE(run-length encoding)是一个压缩算法，它最大的好处就是解压速度快。用来做嵌入式设备开机时的LOGO是不错的选择，android里也使用了这种格式。今天写了个小工具jpeg2rle，它把JPEG文件转换成RLE文件。

o 把一行数据写入RLE文件。

void
put_scanline_to_file (FILE * outfile, char *scanline, int width,
                    int row_stride)
{
    int i = 0;
    char *pixels = scanline;
    char *start = scanline;
 
    while (i < width)
    {
        unsigned short n = 0;
        for (; i < width; i++, n++)
        {
            if (memcmp (pixels, pixels + 3 * n, 3) != 0)
            {
                break;
            }
        }
        unsigned char r = pixels[0];
        unsigned char g = pixels[1];
        unsigned char b = pixels[2];
        unsigned short rle565 = ((r >> 3) << 11) | ((g >> 2) << 5) | (b >> 3);
 
        fwrite (&n, 2, 1, outfile);
        fwrite (&rle565, 2, 1, outfile);
        pixels += 3 * n;
    }
 
    return;
}

o 解压jpeg

 
int jpeg2rle (char *filename, char *outfilename)
{
    struct jpeg_decompress_struct cinfo;
    int i = 0;
    struct my_error_mgr jerr;
    FILE *infile;
    FILE *outfile;
    JSAMPARRAY buffer;
    int row_stride;
 
    if ((infile = fopen (filename, "rb")) == NULL)
    {
        fprintf (stderr, "can't open %s/n", filename);
        return 0;
    }
 
    if ((outfile = fopen (outfilename, "wb")) == NULL)
    {
        fprintf (stderr, "can't open %s/n", outfilename);
        fclose (infile);
        return 0;
    }
 
    cinfo.err = jpeg_std_error (&jerr.pub);
    jerr.pub.error_exit = my_error_exit;
 
    if (setjmp (jerr.setjmp_buffer))
    {
        jpeg_destroy_decompress (&cinfo);
        fclose (infile);
        fclose (outfile);
        return 0;
    }
    jpeg_create_decompress (&cinfo);
    jpeg_stdio_src (&cinfo, infile);
 
    (void) jpeg_read_header (&cinfo, TRUE);
    (void) jpeg_start_decompress (&cinfo);
    row_stride = cinfo.output_width * cinfo.output_components;
    buffer = (*cinfo.mem->alloc_sarray)
        ((j_common_ptr) & cinfo, JPOOL_IMAGE, row_stride, 1);
    printf("size: %dx%d/n", cinfo.output_width, cinfo.output_height);
    while (cinfo.output_scanline < cinfo.output_height)
    {
        (void) jpeg_read_scanlines (&cinfo, buffer, 1);
        put_scanline_to_file (outfile, buffer[0], cinfo.output_width,
                row_stride);
    }
 
    (void) jpeg_finish_decompress (&cinfo);
    jpeg_destroy_decompress (&cinfo);
 
    fclose (infile);
    fclose (outfile);
 
    return 1;
}

o 主函数

int main (int argc, char *argv[])
{
    if (argc != 3)
    {
        printf ("usage: %s jpeg rle/n", argv[0]);
    }
    else
    {
        jpeg2rle(argv[1], argv[2]);
    }
 
    return 0;
}

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