Featured image on posts is blurry

Hi,

The blog post’s feature image is blurry. No matter what size we set, it would automatically regenerate?the image to 640×300 px.?

We’ve tried to set setting > media size to all 0.

And put these code in the child theme functional php.

add_filter(‘jpeg_quality’, create_function(”, ‘return 100;’));

function chnage_filter_image_sizes($sizes){
    $sizes = array();
    return $sizes;
}
add_filter(‘intermediate_image_sizes_advanced’, ‘chnage_filter_image_sizes’);

Both not working. We’d be super appreciative for any help.

WordPress version: 3.1.4. Template: Madidus

We also have a look at https://www.ads-software.com/support/topic/featured-image-on-posts-is-blurry/ but unfortunately our wordpress version is too low to download the plugin.

The page I need help with: [log in to see the link]