How to use background images (LDR) and bloom?

[blank...]

I have this project and I want to do as much in Corona, and as little in post as possible. Besides, I really like Coronas bloom, it has directionality and it just looks nice so there is no excuse to not use it.
Except, it works only with what it sees, making it hard (impossible?) to get bloom from exterior, i.e. windows if there is anything other then CoronaSky as background.

Image 01
Let's start with nothing except CoronaSky as background, everything works as expected.



Image 02
Add background image as Direct visibility override, no more bloom.


Image 03
No problem, I'll just go the old fashion way with plane in the background and Light material, right? Wrong! Same result even though plane is set to not receive or cast shadows, or even visible to reflections/refractions.


Image 04
But, if I pipe it through Rayswithcher map, plugging CoronaSky for global illumination and background image as everything else, then it has to work, right!? Wrong! The same result.


So, does bloom work only with what it sees, making it hard (impossible?) to get bloom from exterior, i.e. windows if there is anything other then CoronaSky as background?
Or am I completely missing something?
Or is this a bug?

Thanks in advance!

[Juraj]

It's a framebuffer post-process, so if the current image doesn't show hot pixels, nothing will diffuse from it. It has nothing to do with Corona Sun/Sky.
I totally get what you want, I wanted to do it recently too. I wanted bloom pass to hold bloom/glare from sun but I had black override because I would be using different background and I wanted perfect anti-aliasing.

Interested if there's any solution to this without workaround. I can imagine having it as function of Corona Output map ( framebuffer would see high dynamic image internally, but would display and compute AA from correct override ).

[blank...]

It's a framebuffer post-process, so if the current image doesn't show hot pixels, nothing will diffuse from it. It has nothing to do with Corona Sun/Sky.

I was hoping someone smarter worked something out about this :)

Though in your case, if you want to add background with exposure so radically different from interior lighting, the bloom pass will look weird.

Nah, I comically exaggerated it to better illustrate the problem.

Interested if there's any solution to this without workaround.

The only "workaround" I came up is to render normally with direct visibility set to black and bloom off. Then turn override off, turn render elements on, with CShading_BloomGlare and just let 5 passes go by. Then add background and composite the whole thing in post.
Coronas bloom really does look better then Fusions, or more "natural".

EDIT: you know what would be great, if Coronas sky had the option to plug a map in it, like Mental rays Sky map!

[Juraj]

Then turn override off, turn render elements on, with CShading_BloomGlare

This works ? I had presumed BloomGlare pass would be empty (black) in this case.

I always need to temporary turn LUT off because it affects the pass, which then isn't possible to composite properly.

[blank...]

This works ? I had presumed BloomGlare pass would be empty (black) in this case.

It works, not sure if you understood me / if I explained clearly. You have to render the same thing twice, first time for beauty, second time to get CShading_BloomGlare element, override turned off so there is Corona sky as background. This second render just needs a couple of passes, but still, it would be great if there was a "fix" for this.

[Juraj]

I thought by "turn render elements on" you meant turn "render elements only/disable shading" :- ) I made that equivalency because I didn't see reason not to have elements always.