static inline unsigned char get_pixel_color(size_t n, size_t row)
{
    return ((n & (1LLU << (nstripes - 1LLU - row)))
            ? static_cast<unsigned char>('\xc0')
            : static_cast<unsigned char>('\x40'));
}
static inline unsigned char get_pixel_color(size_t n, size_t row)
{
    return ((n & (1LLU << (nstripes - 1LLU - row)))
            ? static_cast<unsigned char>('\xc0')
            : static_cast<unsigned char>('\x40'));
}