The reason you find this very hard to do is because of the way photoshop, and a few other notable exception, assumes you want to handle alpha. The problem does not to my knowlege happen in many other applications, this is extremely simple in, shake , fusion, even after effects. But is insanely hard to do with prohotoshop or some other still image editors in general because the load module just destroys the the entire alpha data. You can substitute the photoshop load plugins for formats with older versions, or things like older super png loader this makes your life MUCH easier. on this fornt but makes 90% of all your OTHER work suck. In fact ohotoshop used to work the way you want to back in 2000 or so, which is why its possible to revert back to this behaviour.
So if you use photohsop theres relally no nice way to do this Photoshop destroyed the image on load. Its a age old alpha inetrpretation thing, and in this case there exists 2 differetn camps of tought. Staright or premultiplied, thing is the premultipled makes little sense to photosop users in general terms. But when doing 3d graphics its the natural outcome. Now it just so happens thet premultipled alpha is much used in video stuff and all but heard of in still pictures world*.
Anyway its not very hard as i told you jsut set the mode to add and subtract alpha form channel behimnd and it works. BUT THIS DOES NOT WORK OUT IN PHOTOSHOP** You can work aroud photoshop but not much point in doing that just switch the load module.
without the post glow as a work around?
Glow is post no matter what, so it can never be a workaround to make post glow. I it was then it would be a workaround by definition.
- who try to pretend the problem does not exist.
** there are 10 or so very freaking big design mistakes in photoshop that will when you know more about image processing that WILL make you loathe the program.
PS: this all is pretty easy to prove, so you doesn't have to take my word for it. But i have no interest in this proof per see. Anyway try saving file without alpha and one with just alpha fill alpha with black, put the non alpha version on top of the alpha balck layer and put the topmost layer to linear dodge which is basically what photoshop calls add. which is basically 3 clicks in any sane comp app. Hiwever theres a more natural routine for this render scene without glow then form commandline just glow with no alpha and load that layer on top with add mode.