Corona Renderer Forum

[Cynthia Skane]

Nowthe big question, why post it on odforce. Primarily because it's essentially a Pathtracer and it's ridiculously fast. Frankly i have never seen a path tracing renderer running on CPU, not GPU, go this fast.

You can never really compare render speeds between different renderers, unless they use roughly the same technology. Now, I believe that Mantra PBR is also a pathtracer, ( If I am wrong, please correct me.)

So I decided to render roughly similar scenes in Mantra and Corona. The model is pretty simple, Its a toy truck, with glossy reflections on pretty much everything, and two really massive area lights. Since Corona was happier to do it with two planes with a constant shader, that's what I used in 3dsmax. I am posting the images below.

The performance of GPU accelerated renderers is impressive. Equally impressive is their list of caveats like hair, motion blur, displacements, instances, volumes, programmable shaders and geometry attributes, graphics card memory limits, and so on. I don't think I've ever worked on a show or commercial that could be done with a GPU accelerated renderer. A few shots here and there but overall they're just not ready for production. The tasks they are superb for are product renderings and architecture since those often don't need more advanced rendering features like volumes and hair (or any of the other stuff that doesn't work with GPU accelerated renderers).

Corona is a CPU engine, still a couple of questions about features set rise, like programmable rendering engine, primitive versatility, motion blur and the rest of a gang mentioned by Luke. Another point is methodology, the scene you posted really doesn't say much about any renderer. Same as row parameter setttings (ray depth).

To sum it up flexibility and controllability are more important than performance to me. If I can have both that's great, but given one or the other I'd rather be able to get a shot done slowly than not at all.

As it's still in alpha, there are a lot of things missing. Right now it doesn't even render particles let alone hair and fur. Also I believe they are aiming at architectural visualization as a primary market as a start so I don't know if a programmable render engine is very high up on their list. I dont think they are aiming for the film and vfx market in the beginning.

If Mantra can be sped up to the point of corona( for simpler renders), Houdini can be a used in a lot more markets. Because markets like Arch viz and product renders dont really need any of the stuff that film renderings require, like hair and fur, motion blur or programmable shaders. DOF can be easily faked in any compositing software.

I have always thought that Houdini would be great for Arch Viz. Once the building has been modeled, populating the scene and environment generation would be so much more easier in Houdini. But, there is no getting around the fact that for this kind of work Mantra is definitely not the best candidate for those sort of renderings especially when you have something like Vray around.

I am posting a few more renders from Corona. They are all between 30-55 min range, but mostly towards product renders and arch viz. And with the quality I have been getting, Corona is certainly production ready for those two fields.

Also It would be great if you could post a render which has better settings and render time. I still sometimes struggle with PBR as to the settings. Mostly I just play with the Samples and the min/max settings. I believe that the max settings is just an upper limit which doesn't really have much of an effect on rendertime. Which was why I set it to 64. But If I am wrong , do let me know.

I don't know anything about Corona, looks like a decent render (as many these days of equal and free access to knowledge and opensource components...) but you are missing the point. First, the market by choice of both renders has a crucial impact on what both of them will be good at, and the more specialized they are, the more differences in particular scenario they will have. This is exactly the (theoretical) reason, why Corona might (theoretically) be better at rendering static, triangles solely scenes, with no material overwrites, no displacements, no geometry attribute driven shaders etc, no deformation blur, AOVs etc etc.

Theoretically, because.... your comparison is inaccurate. This scene can be rendered in Mantra in less than 10 minute, with comparable quality on my old dual core laptop (Core Duo T9500) Divide it by at least 2 (or 4 actually) to get the spec of your Intel i...@2.66 and note, that quality of my try is slightly higher (but the resolution little lower).

your renders are faulty, because you seem to be lighting and rendering in sRGB space. I don't know how Corona handles this, but generally speaking physically based renders are sensitive on color space issues. I had to adjust your scene for linear color space workflow, which significantly helps Mantra to resolve sampling noise.

Firstly, Erik thanks about the Noise level parameter, never really tried that before. Got my render time down significantly, but what was 9.40 on your system became 30.21 on my system. I guess there is a pretty big difference between the i7 920 and the i7 2400K.

Could you explain about the whole sRGB and linear space stuff. I know what they mean but where do you access them from in Houdini. Also would be better if you could just upload the hip file, so I could check out the changes you have made.

SYmek, I was basically just comparing the speed of a Corona to Mantra on a simple enough scene which wasn't dependent on any sort of attributes. But if the speed difference is just mainly due to my lack of knowledge, then that is really good news, because it means that I get to learn something new.

Stick to Mantra if you want to render animation sequence with hair,fire,smoke volume and shit loads of geometry.Every week , there is a new fancy renderer popping up and they come and go.Mantra doesn't and you can thank me later.

What a perfect file to warp and twist a render's performance. Super simple geometry with no surface complexity what so ever. Simplistic lighting scenario. Perfect set-up to turn Mantra's PBR defaults sideways but if you know a bit about how to approach such a scene, you can dial it in and get super reasonable render times out of Mantra.

Just looking at your file, yeah you had the primary samples jacked which is what I find most everyone does when they first try to get clean PBR renders. I really want to have a reorganized interface in a Mantra ROP tailored to just do PBR.

My approach with PBR and Mantra these days is to set the primary Pixel Samples as low as you can to resolve the geometry detail itself and if there are fine displacements or high frequency textures, then and only then will I start cranking up the primary Pixel Samples if I can't resolve that "primary" detail. I call these "primary" as they are the bare minimum that Mantra will fire at the given bit of surface under the current pixel being shaded. These are the first set of rays that find geometry (including fine curves and displacements), resolve geometric detail and run shaders to draw texture maps and procedurals.

After that, secondary rays are fired at the same bundle amount set by Pixel Samples when the noise threshold hasn't been met. The Min Pixel Samples I rarely set above 1. The Max Pixel Samples defaulting to 9 I don't change unless I start lowering the noise threshold below 0.02 or 2 percent variation in the returned pixel samples. The max Pixel Samples is a maximum threshold for number of Pixel Sample passes to perform in order to reduce the noise to your given noise tolerance. Either you run out of secondary ray multipliers on the Pixel Samples or you reach your noise threshold.

When rendering with PBR, you must set the gamma to 2.2 or use a proper sRGB lut to compensate for your monitor OS settings. It assumes that your images will be color corrected with a gamma 2.2 set. If not, you will adjust your lights for things to look good and that will cause your darks to be artificially too dark with the result being much more noise. I wonder if this given render engine is Fisher Price'ing the linear lighting process by doing this all behind the scenes for you. I won't tell you the amount of heat we'll take in Support if we ever tinker toy'ed the interface...

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