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add_image_size('generic-small', 200, false);
add_image_size('generic-medium', 400, false);
add_image_size('generic-large', 600, false);
add_image_size('generic-xl', 800, false);
add_image_size('generic-xxl', 1200, false);

add_filter('image_size_names_choose', 'my_custom_sizes');
function my_custom_sizes($sizes)
{
    return array_merge($sizes, array(
        'generic-small'          => __('Generic Small'),
        'generic-medium'         => __('Generic Medium'),
        'generic-large'          => __('Generic Large'),
        'generic-xl'             => __('Generic XL'),
        'generic-xxl'            => __('Generic XXL'),
        'medium_large'           => __('Medium Large'),
        'wysija-newsletters-max' => __('Newsletter'),
        'blog-large'             => __('Blog Large'),
        'blog-medium'            => __('Blog Medium'),
        'portfolio-full'         => __('Portfolio Full'),
        'portfolio-one'          => __('Portfolio One'),
        'portfolio-two'          => __('Portfolio Two'),
        'portfolio-three'        => __('Portfolio Three'),
        'portfolio-five'         => __('Portfolio Five'),
        'recent-posts'           => __('Recent Posts'),
        'recent-works-thumbnail' => __('Recent Works Thumbnail'),
        'easy_testimonial_thumb' => __('Easy Testimonials'),
    ));
}