I came around something strange, maybe one in here can clearify.
Very simple setup and i’m wondering if it was possible easily in the past.
A backdrop and a vray light behind, which should be function as a rim light,
excluding the backdrop and reflecting on the teapot.
Somehow in the latest vray version, i’m not able to make this work.
No matter if i exclude the backdrop or include the teapot.
Only diffuse is passing through and it’s lighting only the teapot (correct)
but no specular is showing up.
Intended?
It’s the same thing as in the thread you linked. Basically, the camera rays hit the teapot, go through the excluded backdrop, and end in the VRayLight. This works straightforwardly with diffuse lighting. However, when the camera ray hits the teapot (which is reflective), reflection rays are cast to find out what to reflect. These reflection rays see the unlit backplate (black), instead of the VRayLight. When you disable the “Visible in Reflections” of the backplate, then it will be invisible for reflection rays, hence the light behind can pass through.
yeah, it definitely works now as you describe and i got your point.
However, my confusion maybe arise from my memory (they can be wrong, right!) as i’m quite sure it was different in the past.
Soo, i remembered an old tutorial by @JonasNoll , and funnily you can see it working in there. D’uh!
Please have a look, should start at the right second:
In the end, it’s just the freedom of placement the light.
So, when i get it right, now, whether you have the place like in a real photoshot, in front of the backplate.
Or, you turn off reflection of the backplate. But that’s causing further problems down the road.
I.e. in a studio setup, you actually want to see the ground reflecting, right?
Kinda awkward case don’t you think?
I think that’s because Chaos changed the way the Specular/Reflection works in later versions. So in the tutorial you linked that still was based on the “legacy” way (which made much more sense in my opinion). Lateron this was changed and I guess it’s because of this why this doesn’t work anymore as you expect.
I also made a video about this where I expressed my wish to reverse this decision again: https://youtu.be/jE56b9PHd1A?si=Pmxangg6CFeTyzrT&t=306
I don’t think the current topic has anything to do with the consistent render elements. Tried the same setup in V-Ray 5, and it works similarly. The reason it works in the video is that the light is not entirely obscured. I’m pretty sure if you were to disable the planes’ “visible in reflections” option in the scene from the video, there would be different highlights (more of them) on the chair. You can try it for yourself—place the light as in the video, and you’ll see that you get some specular (only from the rays that hit the light directly).
I think the difference is that before the Specular component of the light was working much more like the Diffuse Component. So if you placed the light behind the wall and excluded the wall from it (or disabled the “Cast Shadow” option in the object properties) then the Specular component of the light still came through (same like the diffuse component now), while only the “raytraced” physical reflections of the light source were blocked by the wall.
But now Specular and Reflection are kind of the same thing and it depends on the glossiness of the material if the reflection is treated as “Specular” or “Reflection”. At least that’s how I got to understand it now. But I’m actually not entirely sure as I might not have understood this new way entirely and why it was changed
I opened the tutorial scene with the chair again in V-Ray 7 and now it does look different from the video as the wall is blocking now both Reflections and Specular and only the Diffuse Component can pass through. So something has definitely changed compared to before.
On one side, i was thinking the same, like what you’re saying. The light is not completely obscured. could that be the reason.
BUT, on the other side. I’m quite sure i had a lot of scenes in the past where the light definitely was totally obscured.
I.e. think about a car interior and you want to place an extra highlight on a radio knob or such.
How would you do that now?
I can remember some trick like not excluding the backdrop but including only the teapot instead in that case.
We just tested this in V-Ray NEXT, and it is the same behaviour. If you have an old scene that did this differently, do send it.
EDIT: Another workaround is to apply a VRayOverrideMtl to the backdrop, where the Reflection material is mapped with a pure black opacity map (fully transparent). Or by excluding the reflections of the backdrop through the Teapot’s Trace Sets (reflections exclude).
01_video.png: The reference frame from the original video (not sure what V-Ray version that was, but it was before the change in Specular/Reflection)
02_vrayNow.png: The same scene rendered with V-Ray now. You can see it renders differently. Most of the specular is blocked by the wall now.
03_vrayNow_noWall.png: You can see if I hide the wall now the whole specular shows now on the chair (same like in 01_video.png). So that means BEFORE the specular was not blocked by the wall, while NOW it is blocked.
chhh, apologies, but with the danger of being annoying, i think Jonas and me do have a point here, don’t we
I stick with my example question, how would you place some “extra” specs in your scene without getting awkwardly complicated now? Not possible?
@JonasNoll could you somehow find which version of V-Ray was the first render done in? In the video description, it just says V-Ray 5.
@olika There doesn’t seem to be an out-of-the-box way since it wouldn’t be physically accurate. Peter Matanov mentioned this in a comment under the improvements yt video, regarding the consistent render elements change.
To be fair: Before placing highlights that were not blocked by excluded geometry inbetween also only worked if you had shaders which had low glossiness values. At this time “Specular” was basically this not really definied highlight similar like for example in a simple Phong Shader while “Reflections” were the “raytraced” and “accurate” phyiscal reflection of the lightsource and shape itself. It’s probably not the correct technical terminology, but that’s how I understood it So Reflections were always blocked by excluded Geometry while Specular was able to pass through if you excluded Geometry or disable “Cast Shadows” for the geometry. As said Specular was working much more similar like Diffuse back then…
But if you wanted to place crisp highlights on chromy objects for example your glossiness would be glose to 1, so the Specular had basically no effect. Thats why in my example you can also only see a difference in the leather chair material but not on the chrome legs.
@hermit.crab : The video was published Nov 15, 2020. As I always use the latest official release it should be whatever release was available at this date.
Ok, you are right. It used to work only if the glossiness was below 1. And it seems not to work that way from 6.00.06 probably because of a certain bug fix (Evaluate diffuse and specular separately only for non-volume hits with VRayLight Affect atmospherics). Either way, I need to discuss this with the devs and product managers and make a decision on whether to leave it as it is or not.
I have wanted this for a long time. It would be exceedingly helpful for product lighting to be able to have a highlight come through when you exclude an object. I run into this all the time, and often have to render a separate pass do to this limitation.
little add on,
you’re right, the example scene was a bit off, as the teapot shader indeed had a glossiness of 1.0 (which is rarely the case and surely never been the case in my older scenes i’m referring to)
Opened it up again and turned glossiness down to 0.8. And like you described above, that’s a different behavior when it’s not at 1.0.
A little hack around is to turn off diffuse AND shadow, so you get kind of super spec which goes through everything.
So, no include/exclude at all. Although you could just include the teapot if needed.
Depending on the shape of your model, this could work or not.
While this would simplify the workflow, it violates physical plausibility.
We didn’t have any issues like these in the past since our setups are mostly built like in the real world.
But remember, we are in advertising… there is reality; then there is perceived reality. Clients usually want the latter.
We try to use physically correct whenever possible, but once you get into small scale there are frequently things where the client wants them physically incorrect. In real world photography they get retouched to look physically incorrect as well.
A very common example is a highlight running all the way down a cylinder (think beverage can). When that cylinder is sitting on a flat surface this only happens at very specific angles; however, this is common request in both CG and in retouching to carry the highlight to the base of the can.
The way vray works now this is a pain because a light below the table surface cannot make a highlight all the way down on the can.
In vehicle real world photography it is not uncommon to have lights or reflectors in the frame in order to get the highlights in the desired location. These then have to be removed in post. The goal is to show the shape of the subject. Even before retouching we would sometimes do such tricks with multiple exposures on a large format camera.
Tools should not be limited based on real world rules, or we would just take photos without any retouching.
