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Redshift - Exclude light from reflection but still affect specular lighting


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Hey guys,

Trying to figure out if it's possible to get a redshift light to be hidden from reflections such as puddles, but still affect the scene normally (specular lighting & diffuse etc).

I recall an 'affect specular' tab for lights in redshift 2.6 but I no longer see this in redshift 3.0, can't remember if that helped at all though.

For my setup I've got a car with 2 headlight ies lights, as well as an area light to the left of the car.
Cinema_4D_0x0koHlmuI.png.ea949efdc67d6767364a477fb53ac524.png

This is a render with the ray contributions left at default. I've got nice specular highlights on the road surface, however the rectangular shape of the area light and the ies lights are visible in the road's reflection.
csHqEz3TlB.png.5bd6523dcdf05ebe10dd424c94dba6e3.png
I've tried turning off the reflection in the details tab of all 3 lights, however this removes any specular lighting on the road and ends up looking flat.HZnCG6ydBc.png.af9c11e39b5c5a649edc4eab07aec8ca.png
and here's some images of the 'object' and 'details' tabs for the lights. As aforementioned I can't see any 'affect specular' option.
Cinema_4D_GfsFlKtsaT.png.820813294a072e9293e11b88941b67b0.pngCinema_4D_9fYcoldK2x.png.89440a1d37bd80ba85af678d6d7aa11f.png

Thanks for your time :)
-Dave

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1 hour ago, digitaldave said:

Hmm I'll have a crack at this cheers! Pretty frustrating as Octane has light linking which can do this easily.

 

Redshift does have light linking:

In the light go to the project tab. Drag the object whose linking you want to affect into the objects list. Exclude or Include. That's light linking in Rs.

 

I'll be honest and say i'm a bit confused about what you actually want here. In your first post you say you want the : "light to be hidden from reflections such as puddles, but still affect the scene normally (specular lighting & diffuse etc" (emphasis is mine). But specular **is** reflection in a PBR based renderer.

 

In a later post you say: you "...want the headlights to affect the road" but "the light itself shows in the road's reflection". In this shot set up isn't most (all?) of the 'effect on the road' the reflection?


You can either have reflection - which includes 'specular' reflection - or not.
You can have a light affect a particular object - or not.

 

Or am I misunderstanding something here?

 

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My bad, didn't know the 'exclude' or 'include' options were light linking, I use em all the time.

To clarify I'm trying to retain the specular highlights and reflections that are cast by the lights, but I don't want the light source itself (those thin streaky headlights) to be shown in the puddles. I'm not even sure if this is possible so please let me know If I'm approaching this the wrong way.

I've asked on the Redshift reddit and a user gave me the following answer, let me know your thoughts:

firefox_Np71WZgXuy.png.b4603dea283341cddfcde9036778f700.png

cheers,
Dave

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A reflection of a light source in a puddle *is* the light source being visible in a puddle. 

 

A reflection of yourself in a mirror *is* you being visible in the mirror - same thing. Except you're a vampire 😄

 

If you are not happy with the look, try changing the light source (e.g. with a light texture/gobo, or change the light's shape/position/rotation) or change the material of the puddle.

 

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OK - I think I understand what you want. I don't think it's achievable directly in render because the 'effect on the road' and the 'headlight reflections' are the same thing from the same light - just reflections. It's a bit like looking in keppn's mirror and seeing your reflection and saying - 'but I don't want to see my head' : )

 

Assuming this is a still for now I think your best option is a 10 minute Photoshop retouch in post.
Light group AOV's and re-assemble in post would be of no benefit at all.

 

I don't think this would be possible in any modern PBR based renderer - but I'd be interested to know if it is : )

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15 hours ago, keppn said:

A reflection of a light source in a puddle *is* the light source being visible in a puddle. 

 

A reflection of yourself in a mirror *is* you being visible in the mirror - same thing. Except you're a vampire 😄

 

If you are not happy with the look, try changing the light source (e.g. with a light texture/gobo, or change the light's shape/position/rotation) or change the material of the puddle.

 

Yeah that is what I figured, I was just curious if there was a way to cheat this. Love the analogy!

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8 hours ago, Mike A said:

OK - I think I understand what you want. I don't think it's achievable directly in render because the 'effect on the road' and the 'headlight reflections' are the same thing from the same light - just reflections. It's a bit like looking in keppn's mirror and seeing your reflection and saying - 'but I don't want to see my head' : )

 

Assuming this is a still for now I think your best option is a 10 minute Photoshop retouch in post.
Light group AOV's and re-assemble in post would be of no benefit at all.

 

I don't think this would be possible in any modern PBR based renderer - but I'd be interested to know if it is : )

Thanks for the response, I now understand separating the reflection of the light source and the specular lighting isn't possible 🙂 

It's an animation unfortunately so gonna cause me a bit more grief. I don't fully understand light group AOV's so would you be able to explain why they wouldn't be beneficial?





 

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I don't know how familiar you are with rebuilding an image from AOV's - so excuse me if I'm stating what you know. To use AOV light groups, that's what you'd need to do - rebuild your render from a stack of AOV's.
Rather than render out a single 'beauty' image per frame, you'd render out multiple AOV's each containing separate contributing elements such as diffuse lighting, global illumination, reflection, refraction, emission etc, and then composite those together in software such as After Effects, Fusion or Nuke to give you the final composite image. This would match your single-render beauty if no changes were made. This does give you the ability to modify the contributions of those various elements in post. The downside is the additional complexity and work of building and rendering that 2D composite.

 

A light group AOV would enable you create separate AOV sets for specified lights. For example, you could have a group for the headlights, and a group for the indicator lights and a group for any environmental lights. That would enable you to manage the relative contributions of those lights in the composite.

 

The reason this would be of no use here - is that the situation would remain exactly as before. Whatever light group your headlight was in, it's reflection would be as you see it here - as a whole - the broken reflection on the road surface and the stronger vertical reflection. Putting it into a light group won't change that.

 

The key thing to understand here is that a 'specular highlight' and a 'reflection' are one thing - just a reflection.  To describe something as having a 'specular highlight' is just the same as saying 'it's got a sharply focused reflection'. 

 

 

Maybe I should ask why you want to get rid of that long vertical streak reflection - because it is realistic : )

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