How to change size image when user WP_Customize_Image_Control on customize

I too would like to know this.

Thanks

All I can pull out from the get_theme_mod() is the url of the image. I would like to specify the image size I have set in the functions.php

Hi,
i came a cross this and this is working fine

$wp_customize->add_control( new WP_Customize_Cropped_Image_Control( $wp_customize, 'cropped_image', array(
    'section'     => 'background_image',
    'label'       => __( 'Croppable Image' ),
    'flex_width'  => true, // Allow any width, making the specified value recommended. False by default.
    'flex_height' => false, // Require the resulting image to be exactly as tall as the height attribute (default).
    'width'       => 1920,
    'height'      => 1080,
) ) );