void
scanline_calculate_result(gint32 image_ID, gdouble* scanline) {



    gint32 active_drawable;
    GimpDrawable* active_drawable_pt;
    GimpPixelRgn pr;
    gint w,h;
    struct scanline sline;

    active_drawable=gimp_image_get_active_drawable(image_ID);
    active_drawable_pt = gimp_drawable_get(active_drawable);

    w = gimp_drawable_width(active_drawable);
    h = gimp_drawable_height(active_drawable);
    gimp_pixel_rgn_init(&pr,
            active_drawable_pt,
            0,
            0,
            w,
            h,
            FALSE,
            FALSE);


    guchar *buf = malloc(w*h*4);
    gimp_pixel_rgn_get_rect(&pr, buf,0,0,w,h);
/* manipulate buf as a bitmap of size wxh */
/* here depending on the image used, i get different results */


    gimp_drawable_detach(active_drawable_pt);

}