Allegro位图命令返回黑屏

#include <allegro.h>
BITMAP *red;
int main(){ 
    allegro_init();
    install_keyboard();
    set_color_depth(32);
    set_gfx_mode( GFX_AUTODETECT, 640, 480, 0, 0);  
    red = load_bitmap( \"frago.png\", NULL);      
    acquire_screen();
    blit(red, screen, 0, 0, 0, 0, 480, 360);
    release_screen();
    readkey();
    destroy_bitmap(red);
    return 0;    
}   
END_OF_MAIN();

PALETTE palette;
BITMAP* red = load_bitmap(\"frago.png\", palette);
select_palette(palette);
blit(red, screen, 0, 0, 0, 0, red->w, red->h);
unselect_palette();

set_color_conversion(COLORCONV_TOTAL);

red = load_bitmap(\"frago.png\", NULL);
if(red == NULL)
{
    printf(\"Cannot load frago.png\\n\");
    return 0;
}