When I set an image as the featured image, it appears much brighter in the home page slider than on the actual post. Is this because of the scaling or is this a overlay of some sort? I know there is a hover effect for the post image, so I was unsure if the starting opacity is something other than 0. Thanks for any insight!
Opacity by default for both featured images and images in featured slider are set to 1, so it means that there is no opacity difference between those. Hover effect with opacity effect is applied to featured images and value is set to 0.8. Also there are no different settings such as brightness or whatever set by theme for these images.
The only difference that there is is that WordPress crops featured images and it does slightly affect image quality but it shouldn’t be a huge deal since it is set to 90% by default.
You can change this behavior by adding this code snippet to functions.php file
add_filter( 'jpeg_quality', create_function( '', 'return 100;' ) );
Not sure if it will help but this is the only different that there is between slider images and featured images.