Ok, in this precise example, I'm sitting on a computer with a 16:10 screen, using default game settings for video.ini (same as deleting it, and letting the game generate it's own, except for vsynch enabled) under it's native 1680x1050 resolution. These are spot on for a HD7870. If I try to generate a preview, this will happen:
View attachment 125826
On the right is the original Kunos preview, black studio is the "fixed (with sun)" version on your blog, and AT-Previews Special.ini is in use for PP.
No detailed reflections will be applied, as they remain configured as "static" for better fps ingame, and due to the use of a 16:10 AR, the generated preview file has a wrong dimension (keeping the same vFOV, thus missing "image" on the horizontal, while having extra vertical resolution).
To generate previews, I use custom 16:9 resolution that is 1680x945 (introduced on AMD drivers via registry), and set all sliders ingame to max detail, so I get better AA, AF, Shadows, PP quality and reflections than my daily settings to get the best result when generating previews. By this way, it comes much closer to the original previews on detail level, and the image ends up with the correct AR and resolution:
View attachment 125828
To make this exchange quicker, without having to pre-launch the game to boost settings and then revert to my play settings after generating previews, I have 2 backups of video.ini in my Documents\Assetto Corsa\cfg folder so I just copy and rename them. I'll include them as asked, but there's nothing really special about them.
If your tool supported a way to point it to another video.ini file for generating previews, it'd be very handy for those that use lighter graphic settings on a daily basis for gameplay, than the ones required for the best previews possible.