custom header functions code

/**
 * Implements an optional custom header for A THEME.
 * See http://codex.wordpress.org/Custom_Headers
 *
 * Sets up the WordPress core custom header arguments and settings.
 *
 * @uses add_theme_support() to register support for 3.4 and up.
 * @uses a_theme_admin_header_style() to style wp-admin form.
 * @uses a_theme_admin_header_image() to add custom markup to wp-admin form.
 *
 */
function a_theme_custom_header_setup() {
    $args = array(
        // image (empty to use none).
        'default-image'          => '',

        // Set height and width, with a maximum value for the width.
        'height'                 => 192,
        'width'                  => 740,
        'max-width'              => 740,

        // Support flexible height and width.
        'flex-height'            => true,
        'flex-width'             => true,

        'default-text-color'     => '',
        'header-text'            => false,

        // Random image rotation off by default.
        'random-default'         => false,

        // Callbacks for styling the header and the admin preview.
        'admin-head-callback'    => 'a_theme_admin_header_style',
        'admin-preview-callback' => 'a_theme_admin_header_image',
    );

    add_theme_support( 'custom-header', $args );
}
add_action( 'after_setup_theme', 'a_theme_custom_header_setup' );

/**
 * Styles the header image displayed on the Appearance > Header admin panel.
 *
 * @since A THEME 1.0
 */
function a_theme_admin_header_style() {
?>
    <style type="text/css">
    .appearance_page_custom-header #headimg {
        border: none;
    }
    #headimg h1,
    #headimg h2 {
        line-height: 1.6;
        margin: 0;
        padding: 0;
    }
    #headimg h1 {
        font-size: 30px;
    }
    #headimg h1 a {
        color: #515151;
        text-decoration: none;
    }
    #headimg h1 a:hover {
        color: #21759b;
    }
    #headimg h2 {
        color: #757575;
        font: normal 13px/1.8 "HelveticaNeue-Light", "Helvetica Neue Light", "Helvetica Neue", sans-serif;
        margin-bottom: 24px;
    }
    #headimg img {
        max-width: <?php echo get_theme_support( 'custom-header', 'max-width' ); ?>px;
    }
    </style>
<?php
}

/**
 * Outputs markup to be displayed on the Appearance > Header admin panel.
 * This callback overrides the default markup displayed there.
*/
function a_theme_admin_header_image() {
    ?>
    <div id="headimg">
        <?php
        if ( ! display_header_text() )
            $style = ' style="display:none;"';
        else
            $style = ' style="color:#' . get_header_textcolor() . ';"';
        ?>
        <h1><a id="name"<?php echo $style; ?> onclick="return false;" href="<?php echo esc_url( home_url( '/' ) ); ?>"><?php bloginfo( 'name' ); ?></a></h1>
        <h2 id="desc"<?php echo $style; ?>><?php bloginfo( 'description' ); ?></h2>
        <?php $header_image = get_header_image();
        if ( ! empty( $header_image ) ) : ?>
            <img src="<?php echo esc_url( $header_image ); ?>" class="header-image" width="<?php echo get_custom_header()->width; ?>" height="<?php echo get_custom_header()->height; ?>" alt="" />
        <?php endif; ?>
    </div>
<?php }