Author Topic: Problem Water droplets Caustics effect  (Read 2279 times)

2022-04-05, 15:43:17

tennet

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Hi,

I am trying to achieve a pretty classic water droplet effect using caustics in C4D "Corona Renderer Version: 8 (DailyBuild Feb  2 2022)". I only get very dark render results compared to the real world references. See my attached examples.

My water droplet mesh is 4,5mm in height and the small water puddles are only like 0,3mm thick (extruded above the floor). I have applied a basic water material with 'Caustics Slow' enabled (under refractions). I have tried with and without 'Volumetrics' enabled (played around with many different settings), but no luck.. I have tried many different light setups, like the 'Corona Sun', Corona Area lights and HDR lighting (HDR gradients on a plane).

Any tips or ideas on how I can achieve these real-world water droplet results? Hope someone can help, many thanks!

(Attached is also my test scene so you can test for yourself)

2022-04-05, 16:30:51
Reply #1

Beanzvision

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Hi there,

I had issues with your lighting so I had to replace it. I also added some noise to the surface of the drops. Nothing is smooth in this world ;) Surface imperfections will help create interesting caustic patterns.

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2022-04-05, 19:19:45
Reply #2

tennet

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Hi, many thanks for looking into the scene. The lighting in the scene works here, maybe the HDR was missing in the uploaded scene.. but did you adjust anything in the materials or mesh (or render settings)? Two of your water puddles still look dark, but the one in the top looks a bit brighter. Are there any differencies?

The effect I often see with water drops on a surface (that I’d like to recreate) is that they tend to look brigther on the inside (not refering to the caustics here). At least the color of the floor(inside the droplet) should be as bright as the original, specially in such small water drops?

If I disable caustics in the material then it gets brighter, but then I loose all the real-world effects instead.

Any ideas?

2022-04-05, 20:06:11
Reply #3

pokoy

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The light blue example looks like it could've been photoshopped.
The other two have one big difference wrt to your setup - a reflective surface that reflects the environment. If you're going for exactly the same effect, try to set up your scene in a way that mimics the source as closely as possible, only then can you really tell if it's a problem with the renderer.
Also, I'd always be careful with examples from stock image libraries. They're often photoshopped or have heavy post production, it's much more reliable to shoot something for yourself, that way you can also tell what the lighting/setup looked like exactly.

2022-04-05, 20:27:22
Reply #4

tennet

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Hi pokoy! Definately a good point, my references from google can of course have been retouched, so I should compare this with my own photos and my real world lighting setups.. will do!

But at the same time I choose photos that looked right to me. I may be wrong, but I have done lots of photo retouching of beverages in my work, so I believe I have some understanding of how droplets and liquids should look, and no matter how strong I crank up my Corona lighting, these very thin water puddles/droplets never get any brighter. And that seems wrong, doesn’t it?

I will try to photo some droplets and experiment some more in Corona. Will update my post!

2022-04-05, 22:26:56
Reply #5

davetwo

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Just to chime in - i've done quite a few projects with droplets on shiny surfaces in Corona - and I've frequently found them too dark when I'm using caustics.
I normally make sure I have the water element as a mask so I can adjust them in post.

How much of this is a defficiency in corona vs my preception not matching reality I'm not sure. But there is an example attached.... my gut feeling is that I need something inbetween.





2022-04-05, 22:50:10
Reply #6

tennet

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Thanks for your input! Yep, I think your version without caustics looks much more realistic in this case. Maybe that the droplets would’ve cast som shadows/caustics on the can irl… but hard to say without a reference, it looks good!

The one on the left though, with caustics enabled, looks much too dark… it shouldn’t be like that, so there’s definately something wrong with how Corona calculates this. Or if there’s some setting that I’m not aware of, but I have enabled ’Fast caustic solver’ in the render settings + enabled caustics in the water material.

Would be great if it was possible to render it correctly, without the need to retouch the droplets later. Appreciate any tips or ideas!


2022-07-06, 12:24:26
Reply #7

pokoy

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I did some tests 2 months ago but then all kinds of things got in the way and I only remembered a few days ago.

Attached are two renders of droplets, one with everything 'physically correct', the other one with water opacity set to 0.5 - this will introduce some physically questionable effects (have a look at the glass sphere on the bottom) but may be good enough for what you're trying to get.
Also attached, a render on a metallic surface - I got carried away with the fancy effects but it shows nicely how different it looks depending on the surface. A metallic surface will behave entirely different and show the nice looking gradients like in your reference.

In any case, lighting is key and will be the main deciding factor whether your result looks good or bad, as is keeping geometry close to the real world thing. You really have to try to model and light the objects and environment according to your reference to get there.

Also, you might find these real-world photos interesting:
https://www.pamelalama.com/hydrophobic-typography-2

Have a look how different water can look depending on viewing angle and lighting, it's almost metallic in some shots. I guess there's quite some contrast applied in post, which may be another thing to keep in mind when looking at reference images.

2022-07-06, 13:08:46
Reply #8

tennet

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I did some tests 2 months ago but then all kinds of things got in the way and I only remembered a few days ago.

Attached are two renders of droplets, one with everything 'physically correct', the other one with water opacity set to 0.5 - this will introduce some physically questionable effects (have a look at the glass sphere on the bottom) but may be good enough for what you're trying to get.
Also attached, a render on a metallic surface - I got carried away with the fancy effects but it shows nicely how different it looks depending on the surface. A metallic surface will behave entirely different and show the nice looking gradients like in your reference.

In any case, lighting is key and will be the main deciding factor whether your result looks good or bad, as is keeping geometry close to the real world thing. You really have to try to model and light the objects and environment according to your reference to get there.

Also, you might find these real-world photos interesting:
https://www.pamelalama.com/hydrophobic-typography-2

Have a look how different water can look depending on viewing angle and lighting, it's almost metallic in some shots. I guess there's quite some contrast applied in post, which may be another thing to keep in mind when looking at reference images.

Hi Pokoy,

Many thanks for getting back to this topic. I think your results look really good, both the version with the opacity set to ’1’ and the version with the metallic surface. They look pretty much as I expect the water droplets to behave in real world etc. This is the effect I am after, but no matter what I tried I didn’t reach any results like these..

Any chance you can share your Cinema 4D scene with me or at least a simpler version of it, just so I can try to get the same results? Are there any settings you are using that I may have missed? Or settings for the water material..

Did you do any post-work to your renders?

Thanks again, appreciate any help I can get with this!

2022-07-06, 13:30:23
Reply #9

pokoy

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I'm on Max but I can export a OBJ file of the scene. I'd replace the lights with geometry with the same dimensions and write down the settings so you can replicate them, no problem.
Water material is simply a CoronaPhysical mtl with IOR of 1.33, refraction set 1.0 and caustics ticked on. Underlying surface material would be up to you but it's really nothing fancy.

One thing I found out while testing is that increasing caustic 'photons per iteration' to 8000-8500 gives a cleaner result (default is 5000, using 10000 makes it unbearably slow). This is something I've been struggling with as most of my caustic tests never cleaned up, there was always some noise that would never resolve.
Also, disabling caustic adaptivity helped, with adaptivity enabled a few droplets missed caustics entirely for some reason, and caustics seemed to calculate slower in general.

I hope I can get you the file tomorrow, Friday latest.

2022-07-06, 14:16:57
Reply #10

tennet

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Many thanks again, sounds great! I hope it is not a problem (or bug) related to the C4D plugin, but at least we will know when I ’ve experimented with your scene setup this weekend..

One thing I forgot to ask you is if you let the droplets cut through the floor geometry (or any geometry that I place the drops onto) or if the water droplets are placed just above the surface of the floor?

2022-07-06, 14:28:01
Reply #11

pokoy

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All water geometry cuts through the plane just a tiny bit, yes. Also, I added some thickness to the plane but I'm not sure it's really needed, I'll test tomorrow to see if it makes a difference.

EDIT - adding thickness or simple plane doesn't make much difference, but I feel like with a bit of thickness the result looks slightly better, even if minimal.
« Last Edit: 2022-07-07, 15:56:33 by pokoy »

2022-07-07, 15:55:36
Reply #12

pokoy

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Here's the scene, external download since file size too big for the forum:

http://www.mswee.net/xchange/220707_Water_Droplets_OBJ_FBX.zip

Details:
- export as OBJ and FBX (FBX keeps scene layers, local pivots and transforms, plus it attempts to keep materials, although many 3dsmax specific maps will not convert correctly, so just make your own)
- since the camera doesn't export, there's a Camera Object and a Camera_Target, use these to position and align your camera correctly
- Camera and Lights have the most important parameter values in their name (radius, intensity, directionality for the lights, for example)
- I've used cm as scene units, probably best to keep it that way
- included the texture used on the lights for a nicer falloff in the reflections
- included two CXR files for 2 of the renders I posted so you can see the post settings from Corona
- water material - refraction on at 1.0, IOR at 1.33
- caustic settings at defaults, only 'photons per iteration' increased to 8500
- Light 01 and 02 were used for the green surface render, Light 03 was used for the metallic surface render, in case you want to get the exact same results

Let me know if you need anything else.

Once you have set it all up and it renders like my green surface example, do a render with only Light 03 instead of Light 01+02 and observe how, suddenly, the water looks flat - similar to your initial setup where you were missing nice looking caustics. That's why trying to reproduce reference images closely is really important, as is the lighting setup to get nice looking results.
« Last Edit: 2022-07-07, 16:06:31 by pokoy »