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How to change default theme thumbnail sizes and cropping settings

You can modify the default theme thumbnail sizes by adding this filter to your child theme functions.php file:

function xt_child_image_sizes($image_sizes) {
    
    return array( 
        'th-small' => array('name'=>'Small', 'width' => 165, 'height' => 84, 'crop' => true), 
        'th-medium' => array('name'=>'Medium','width' => 270, 'height' => 138, 'crop' => true), 
        'th-large' => array('name'=>'Large','width' => 590, 'height' => 300, 'crop' => true), 
        'th-xlarge' => array('name'=>'XLarge','width' => 590, 'height' => 300, 'crop' => true), 
    );
    
}
add_filter('xt_image_sizes', 'xt_child_image_sizes');

From this function you can either modify the $image_sizes array or you can return a new array like the above.
Feel free to modify the width / height of each thumbnail size. You can also set crop to false to keep the original image look.

When this is done, you will need to regenerate all the thumbnails using this plugin

https://wordpress.org/plugins/regenerate-thumbnails/