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DrScarlett

Neon light and area light samples

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Hey Cafe-ers,

 

I have been trying to get good looking and possibly more or less believable neon lights going. I tried both the area light approach as well as the luminance material approach. I like the area lights best because I can do it without GI, the result looks crisp, the falloff looks more natural, I get nice reflections and specular. Also i don't have to muck about with separate objects for GI and camera behavior with compositing tags and compensate for overexposed neon tubes.
Regardless of this preference I am looking for tips to make good neon with vanilla r20.

For now I wanna ask the following. The pic below is a straight physical render using area lights. I am starting to like the overall look. There are two issues:

  • The area light reflections look blotchy (already at a 1000 samples, add grain completely pixelates the reflection). I need more samples in the area lights. Any way to go above a 1000 samples?
  • The bump in the floor reflection is off, the bump channel seems to have shifted and I don't know why.

 

Would anyone have any hints or tips on all of this?

 

Mozyeyz_0015_Area_Light.png

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I can maybe help with the first one...

 

Are you using splines as area lights here, or the (presumably swept) geometry itself ?

 

In either case I can confirm that we can't go above 1000 samples there. But, at the expense of a bit of a Render time hit, we can tick Add grain (adjacent to the samples field in the light), which should entirely eliminate the problem, though you will still want to keep samples fairly high to keep that effect from being too grainy...

 

As far as the bump issue goes, I am not sure what I'm looking at there - to me it seems consistent with the bump on the floor elsewhere, but the texture of the floor is making it difficult to isolate what bump is doing...

 

CBR

 

 

 

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  • Hey Cerbera, thank you.

     

    I am using swept geometry (actually spline wrapped cylinders turned editable), because the lights themselves need to be visible (as the neon gas emanating light) and have a certain thickness. They are inside wider glass tubes. I control their visibility with the visibility modifier.

    I tried the add grain option, but the graininess in the resulting render is terrible (also at a 1000 samples), I don't know how to improve that. I would prefer not to see any grain in the reflection.

     

    I'll focus on this for now and get back to the bump problem once I have this sussed.

    **EDIT: fixed the reflection bump issue, it was a legacy error from previous tile texture

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    I do know what you mean - it's not ideal is it...

    I think perhaps the time has come to try the GI way instead - it might be preferable to avoid it, but if you have no other choice to get the look you want ?

     

    CBR

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  • Hey again,

     

    I tried the GI way before I posted.

    • The rendered results are way too, hmm, fluffy
    • The luminance based light give little in the way of material reflections or specular reflection. Since they are based on GI, the solution might be to muck about with render settings
    • In order to get a decent fall-off behavior of the neon light (fall-off is almost impossible to control), the luminance values need to be completely blown out, resulting in an over exposed neon tube. That in turn forces me to go to a rather complicated composite tag setup with different objects for glass, GI light, and visual representation of the neon gas.

     

    I suppose if I keep throwing render tests at it, I will get there in the end, but render times in my test file are already over the top andit will take me literally weeks.

    Neon scenes are fairly common, I suppose, so maybe you (or someone else) have some other tips or sources that can help me get there faster?

    Meanwhile I am working on an area light version where the neon tube area lights have been cut into sections, controlling the balance of  the light emission and visibility of each section with some Xpresso. This gives me a higher sample density per length of neon tube. Complicated, but easier to manage for me than the GI way. I will post if I get something.

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    What are you camera settings? In a real-world situation, neon is very intense and to get a picture at the levels you are showing, the camera settings need to be precise. It may be that you do need to crank up the light intensity and clamp down the camera, so that there is enough light being pushed through the scene to compensate for the sample rate? Hopefully, your scene is also constructed at real-world scale.

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  • Thank you Vizn, 

    a few follow up questions if you don't mind. Thank you in advance for your time.

     

    • yes indeed, you are right. I know about the difficulties of photographing neon. It is very hard to capture the right balance between the neon light itself and the lighting on the surrounding scene. That I can use the C4D camera to follow the same process hadn't occurred to me. I need to learn how first. I suppose I use the camera exposure settings to do this?
    • If I add more light, how does that fix the lack of samples - I will still have blotches in my reflections and speculars because of the lack of samples, no?
    • Yes the scene is more or less at true scale, though the letters are very big, around a meter high. That is the way I wanted it. The neon glass tubes are 2 cm diameter, the neon light (supposed gas) is 1 cm diameter. What exactly is the relevance of the scale?

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    Modeling to scale benefits the light and shadow calculations as the algorithms are based on the real-world physical properties of light. I suppose if you aren't using GI, then maybe this point is less important, but it's still a good rule to follow most of the time.

     

    Light intensity basically pushes the light further, so the decay or falloff of the light takes longer the more intense it is. As light travels further, it bounces off more surfaces, which all gets added into ambient light levels. Because of this, building your scene materials as physically accurate as possible will help tremendously as well. With more intense lights, nearer surfaces receive more light since it isn't dying as quickly, which should equate to less noise at render.

     

    This might get you going in the right direction: https://www.popphoto.com/how-to/2010/10/how-to-shoot-neon-lights/

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  • Quote

    Light intensity basically pushes the light further, so the decay or falloff of the light takes longer the more intense it is. As light travels further, it bounces off more surfaces, which all gets added into ambient light levels. Because of this, building your scene materials as physically accurate as possible will help tremendously as well. With more intense lights, nearer surfaces receive more light since it isn't dying as quickly, which should equate to less noise at render.

    One thing I would like to clear up, maybe, above we were not talking about rendering noise when we were talking about the maximum amount of samples - this was specifically about an idiosyncrasy of area lights, where you get blotchy reflections and specular reflections based on a specific sample setting of the area light. I can't, unfortunately, bypass that by pushing more light into them. I will still have the blotches, just more bright blotches. Also this idea probably works best with GI, which is what I was trying to avoid due to my lack of rendering power.


    However, the idea is valid, it helps me getting a better, more photo realistic render of the neon lights. I will come back to it - it looks like I might not be able to avoid GI, I have met with a few more problems with cutting up the area lights into pieces. I will show you the results when I am done.

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  • So here are the results from the cutting-the-area-lights-into-pieces method.

    I have cut each spline into 6-12 pieces, and then re-applied the the cylinder shapes with spline wraps to get continuous tubes in the shape of the letters.

     

    First result shows it solves the blotchy reflection problem, however, suddenly different sections of different lengths are giving off different amounts of light.

    mcZyxcK.png

     

    I tried changing the amount of samples in each section - no change. I tried changing the visibility of each section - this only affects the brightness of the tube itself. Only the light intensity seems to have an effect on the reflection brightness of the lights. I ended up making some Xpresso that that controls number of samples, light intensity and light visibility for each section.

    WJ9UO31.png

     

    After 4 or 5 tries I got it all balanced out. This result is pretty okay.

    vUYnKtb.png

     

    However now I discovered a new problem. It is hard to see in the image but the shadows (specifically those of the little clips holding the tubes) go in strange directions. I think this is because in calculating the area shadows, the center of each section of tubing plays a role, or the location of where most of the 'fake light samples' (internal method for creating the object based area lights) are, determine the direction of the shadow casting. Bummer. Another imperfection to the method.

     

    EDIT:

    Here is a high-res version of it, where you can see the strange shadows much better. Also a pretty nice look otherwise. Physical render, no GI. Took 153 hours :(
    C0N0uMe.jpg

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  • So now my next question.

     

    I will go back to trying to simulate the tubes with luminous textures and use GI to get them to render.

    • Would anyone have any tips for the best GI render settings to use in order to get a crisp realistic result in the scene above?
    • Is the polygon light toggle in the texture illumination tab useful to use? Do I need to use QMC to make optimal use of that?

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    On 6/9/2019 at 12:09 AM, DrScarlett said:

    C0N0uMe.jpg

    Looks great! The clip shadows look okay and aren't too distracting to me. I prob wouldn't have noticed if you didn't point them out. What material did you put on them? They look black. Maybe if the material was more of a semi-clear plastic rather than solid black it would help soften the shadows by allowing the light to spread them out more. Perhaps the GI solution would help soften them up as well. I am not familiar enough with C4D's GI and material illumination effects to offer any advice on that, unfortunately. Nice work. Love the detail you put into this.

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