Small wish for Render element Lens Effect

[trixian]

I really really would like if the results you get when telling the glare and bloom passes to be element only, to be set against black. Not for comping through addition, as specially the bloom would brighten stuff behind it, but that they contain an alpha channel for the effect it self and meant for comping on top normally.
Is this particularly hard to do since it has not been implemented, or is it by design that the RE contains the rest of the beauty pass?

[vlado]

What do you mean to be set by black? In the general case, the effects are applied uniformly to the entire image, there is no "alpha" as such.

Best regards,
Vlado

[trixian]

I mean using black as a background so the alpha is multiplied against black. We need a proper alpha to make this work obviously.
As of now, it seems all render elements only inherit the main alpha from the beauty portion of the rendering. My thoughts would be that the bloom and glare specifically need their own alpha so they can be comped "over" the rendering properly. Both these render elements are basically just beauty passes with the specific effect applied to each respective image.
Currently, the RGB and glare\bloom need to be merged and blended beforehand (they cant be added\screened as this is plain wrong and changes the image drastically), and then you can add the spec and reflection on top, which is a rather strange way of doing this.
Effects happening in the lens should always be placed last (relatively) in the compositing chain of events.
Imagine you fancied writing a lens flare effect (not really), and it was written out in the same fashion as the bloom and glare, you would end up with a beauty pass with a baked in lensflare.
How would you comp that?
(Obviously one can try and isolate this through a difference layer, and pipe it back in, but that seems rather unnecessary when the effect could be separated out directly from the rendering).

[vlado]

My thoughts would be that the bloom and glare specifically need their own alpha so they can be comped "over" the rendering properly.

Where would this alpha come from?

Best regards,
Vlado

[vlado]

Both these render elements are basically just beauty passes with the specific effect applied to each respective image.

Yes. But there is no "comping" operation involving "alpha" in that. Both effects practically blur the whole image with a specific blur kernel.

Best regards,
Vlado

[trixian]

The comping I'm referring to is the comping I am doing with my images.
That is the whole reason for selecting the "render element only" option in the dialogue. What is the purpose of having it as an element if you can't composite it correctly afterwards?
If the isolated elements are the same as the unisolated pass (rgb with them both applied), I'd be better off just adjusting them more and rendering them into the beauty pass anyway.

Anyway, they (the VRay LensEffects) only blur\filter the pixels selected through the parameters, like the intensity mask etc. in my case, so I'd say there is already a certain "selection" going on.
Why could it not work like so many other "2d glow" filters out there that let you isolate out your glow from the source image?
It basically falls back to this: How would you propose we composite the bloom and glare passes properly in a comp with other elements like spec\reflect\refract etc. ?

[vlado]

What is the purpose of having it as an element if you can't composite it correctly afterwards?

The correct composition is supposed to be a simple blend with the original image.

Anyway, they (the VRay LensEffects) only blur\filter the pixels selected through the parameters, like the intensity mask etc. in my case, so I'd say there is already a certain "selection" going on.

Yes, I can see where in that case having an alpha might be helpful - will make a note to look into it.

It basically falls back to this: How would you propose we composite the bloom and glare passes properly in a comp with other elements like spec\reflect\refract etc.?

If you intend to compose the image from the other elements, then the bloom/glare elements that V-Ray provides are mostly useless in their current form. In that case it would be best to do these effects in your comp application itself.

Best regards,
Vlado

[trixian]

The correct composition is supposed to be a simple blend with the original image.

Yes, I can see where in that case having an alpha might be helpful - will make a note to look into it.

If you intend to compose the image from the other elements, then the bloom/glare elements that V-Ray provides are mostly useless in their current form. In that case it would be best to do these effects in your comp application itself.

Best regards,
Vlado

Well, in most cases the pre blending with the main rgb beauty works ok.
The reason I brought this up was because using a large bloom and adding in passes after this step would result in reflections brightening the bloom (as it was set to add on top of the bloomed result), and the fact that it just seemed strange the "separated" passes included the complete rbg, so I figured there was room for improvement.

[Dmerc]

+1: had a similar thought recently.

I actually thought about having a pre-effect output additionally to have control if I want to keep the effect or blend it in in post.

A difference composite might then help to filter it out (subtract ...)

BR, Peter