image thumb poor quality, disable compression

hi, i have installed the plugin and are great for functionality, but when generate the thumb the quality are poor, this plugin have a option for compress the image ? i tried to insert this in my functions.php

add_filter( 'jpeg_quality', create_function( '', 'return 100;' ) );

without success.

I tried also to remove image thumb in folder “thumb” and then recreate it without success.

how i can solve ?

thanks

https://wordpress.org/plugins/photo-gallery/