Cineversity

Hello,

I’ve just finished a render and noticed that the specular highlight on small water droplets is flickering.  The highlight comes from an omni light.  Does anyone have suggestions on how I might address the issue?

Increasing the roughness of the specular highlights?

Splitting the light and make a specular highlight using an area light?

Here is a sample from the render…

https://dl.dropboxusercontent.com/u/27222099/JO_waterDrop_RGB_detail.mov.zip

Thanks!

HI Jerome,

I can see the effect. If you have a small (reduced) scene file where I can reproduce it—that would be better.

I’m certainly not a friend of guessing, as it seems more often than not only to waste time on both sides. But: the Metaball object produces for each change a new mesh, there would be my first focus on.
Secondly, it feels like rendered without motion blur, which is certainly not an effect I would suggest here. No motion blur, e.g., short “aperture opening” as in Raytracing typically, produces a “Save Private Ryan” aesthetic, rough to say the least.

Besides that, specular highlights are just an simulation, as I wrote often in the past. It is like an image that is placed on the surface based on the light position and camera position. It just produces something that was given before. Each takes a single spot on the surface, and with that is highly dependent on the Normal calculation, hence the Phong tag settings—but the change is too much anyway.

If you open the scene file below, and press play you will instantly see the problem. Switch the rendering for the Metaball off, but leave it active! Then set the Sphere with the Shrink Wrap to render and compare.

Have a nice Sunday

Sassi

Thank you, Sassi.

Yes, I can see how the spec highlight is dancing all over the metaball.  Thank you for pointing that out.  In my particular case, however, the flickering is happening on static geometry—I should’ve been more clear in my description and also provided you with the scene file, sorry about that.  I think the main culprit here is having a spec highlight that is too sharp on geometry that was too small and low res.  In order to solve the issue, I’ve moved the camera closer to the wall, placing it on a sharper angle and also added a touch more roughness to the spec highlight.  The added benefit of doing this is a shot that looks much better.  There’s more parallax and the TP animation feels more like a macro shot, which looks cooler.

Yes, I am rendering without motion blur as I’m trying to keep my render times as low as possible.  I need to learn and experiment more with rendering and understand what I need and don’t need to get the look that I want while keeping render times as low as possible, but that’ll be for another day—right now, I just need to get the shots out the door and make the client happy.

So far, I’m not noticing any adverse strobe effect (Private Ryan), but if I do, my only solution will be AE’s pixel motion blur for now.

As a side note, I’m also reading Digital Lighting & Rendering which is helping me understand how to break up my scenes for better control, but have only just finished chapter 3.  To complement the reading, I’m following your multi pass rendering series here on Cineversity.  Hopefully, these will help me avoid future issues like the ones I’ve seen this week end.

Either way, this is my first real job using C4D.  I’ll send the render off to the client tomorrow and show them a mesh preview of the next shot.  Hopefully, they’ll be pleased with both.

Again, thank you for all you help, Sassi.  I wouldn’t be able to do this without you.

Jerome

You’re welcome, Jerome.

Water is a tricky material, as it is invisible and lives only based on refraction and light, except when it is contaminated ;o)
So, the specular highlights are certainly an indicator for water, but an HDRI based reflection might be better. Why? Because the light in the HDRimage would anchor the drops more in the world. The Specular highlights are without (real world) effect natively in CG, as a bright light-source that would cause such an effect (specular), would result in caustics, which is as well a render intensive effect. If you can render the drops as alpha mask (in color correction terms, “qualifiers”), you can adjust the brightness a little bit behind the drops, to increase the effect on the “wall”.

However, if you can move the camera dynamically, it might help a lot, to sell any change in the lights, as movement causes similar changes anyway.

Motion blur in post. Well, it is more common than not for 3D render. But post means, you apply something to a single pixel, not layers of material anymore. (Deep Compositing is not available in Ae). Having said that, I like to experiment when time is precious, to separate the background (wall) from the drops (foreground, in a way), at least the specular highlights might be better “motion blurred in a separate pass, and then brought back. What I did in “JET” was to render in SubFrame Motion blur to a small degree, and use then a Motion Pass for Ae, which is not precise nor correct but closer for multilayer materials. Automatic post motion blur is not to my liking, it simplifies too much, but—yes—people get used to this fake as they do got used to fake explosions in space (no one has seen a real one ever, so we believe in a VFX reality).

I talk about this since a decade and I hope that the 4K (UHD) will set the bar a little bit higher, so the results will improve, as it has from SD to HD. However, effective editing and avoiding long single takes will help here of of course.

My best wishes for project

Sassi

Sassi,

You’ve brought up an interesting point.  The HDRI.  I don’t have any for the location as everything was shot on a boat, but I am able to rebuild the boat in C4D.  Is it possible to model something in C4D then render out an HDRI sphere?

If yes, what would be the correct render and camera settings for that?

Jerome

Yes, Jerome, there is a simple way (“simple” perhaps not the first time, but not complicated and certainly easy the second time.)
You need to build perhaps only what the drops might “see” and place the sphere (you soon will know what I have in mind) close to where the drops are.

Have a look here: http://youtu.be/Ows9cjiScmk

This is a single part of one of my series that I upload currently, official announcement later. Two more series to conform (title cards, etc)

Enjoy finishing the project
Sassi