Thumbnail immer auf width="290" stellen

function wp_shrink_dimensions( $width, $height, $wmax = 128, $hmax = 96 ) {

elseif ( $width / $height > 4 / 3 )
		return array( 128, (int) ($height / $width * 128 ));
	else
		return array( (int) ($width / $height * 96 ), 96 );

$max_side = apply_filters( 'wp_thumbnail_max_side_length', 128, $attachment_id, $file );

list($width,$height) = wp_shrink_dimensions($attachment_data['width'], $attachment_data['height'], 171, 128);

echo wp_upload_display( array(171, 128) );