Remove WordPress default image compression

By default, WordPress compresses your images for better performance.

Every time you upload a JPEG image in WordPress, it would automatically compress the image to 90% quality.

All you need to do is paste the following code in your custom plugin's functions.php

add_filter('jpeg_quality', function($arg){return 100;});

When you do make these image quality changes, you want to make sure that you regenerate your thumbnails.

Code snippet taken from this source.