Author Topic: Caustics  (Read 1400 times)

2023-01-25, 11:09:24

Dean81

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Hi All,

I work entirely in product/packaging visualisation and when rendering glass I'd like to use caustics. Try as I might though, I just can't get any decent result. Even when striping out everything in the scene and using a single light it's taking hours to get something half decent and even then it's still pretty poor and so heavy in the noise it's just not worth the time spent.

Are there any particular render setting or should be tinkering with to improve upon the standard ones?

Any help of advice would be much appreciated.

Cheers
D

2023-01-25, 11:49:13
Reply #1

Beanzvision

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Hi there, can you share some examples with us? This example scene took 15 passes at around 7mins and cleaned up nicely. The light source was just the sun and sky.

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2023-01-25, 14:08:18
Reply #2

Dean81

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Well that's just baffling! After 5hrs rendering a scene over night, I ended up with a caustic pass that looked like the attached (1). I then stripped out all the other lights except one sun light (which I increased the strength of) and I'm still only getting the other image attached (2).

If I could get something approaching your example I'd be very happy indeed!!

2023-01-25, 14:20:57
Reply #3

Beanzvision

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Do you have caustics enabled in both the material and also in the render settings under the performance tab? Can you share a test scene that we can look at? I'll supply a test scene as well.
Bengamin Jerrems l chaos-corona.com
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2023-01-25, 15:23:48
Reply #4

Dean81

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Here's the scene file. I stripped out the stuff I couldn't share for confidentiality reasons but this should highlight the problem.

Thank for sending your scene file. I'll take a look shortly.

2023-01-26, 15:57:28
Reply #5

Pepelecrabb

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It is the lighting and scene set up that is the issue, as is almost always the case. Your lighting is very soft which softens the caustics (and shadows) to almost non existence. With the sun setup the lighting is better but the sun and sky intensities are turned way down which may or may not be an issue. I didn't play around with them just set them back to default and adjusted camera settings (Simple Exposure -5.0)

There has been a lot of talk around here about mentoring/tutoring and the most often and correct response is to "think like a photographer". Much easier said then done though. To think like a photographer, one must know how a photographer thinks.

In this scene there are 3 different items with 3 different reflection types and on top of that, caustics and transparency. All that makes it more difficult then one would think.  This dictates the choice in lights and placement in conjunction with how you want it to look. If you want caustics that requires hard directional lighting. If you want big soft sweeping highlights and shadows that requires broad soft lighting. In reality you can't have both. In photography and cgi there are some tricks that can be used to lessen and exaggerate (mostly by compositing) but it quickly looks unnatural to humans that are used to one light source (the sun).

I rendered your scene out using the sun and sky with the camera adjustments I mentioned. Took just under 10 minutes which may be a hardware issue for you.

2023-01-26, 16:47:52
Reply #6

BigAl3D

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Nice. I will add that when thinking like a photographer, you need to NOT use the simple exposure settings, and enable Photographic Exposure. This will give you camera-like settings like ISO, Shutter and F-Stop.

I did a quick test using the Photographic Exposure route and a little more highlight compression. Sky and Sun are at 1, then the camera is adjusted accordingly. If that still doesn't cut it, then adjust the intensity of the Sky or Sun, although Corona strives to be real-world and, at least here in the U.S., I can't adjust the sun to my liking. :-)

I stopped this render at 22 minutes (25 passes) on my old iMac Pro 18-core. For some reason, it did not denoise, but it was going in a good direction. Probably would finish at 45 min. Curious how smooth denoise would have made this. Probably needs more that 25 passes even with denoise.

Helpful discussion.

2023-01-26, 17:41:06
Reply #7

Pepelecrabb

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I usually do not mess with Photographic Exposure unless I am using DOF. Which brings me to another point when thinking like a photographer...I would not use a 600mm lens on a 35mm camera for this kind of shot. The depth of field would be too shallow even at f64, which would then also require a ton of light for correct exposure. A mild telephoto in the 60-120mm range would be perfect for a flat field distortion free lens.

There in lies the beauty of CGI where you can use a 600 mm lens if you want. It doesn't cost you anything and you don't have to climb up a 50 foot ladder to get the shot. But in the end there is no reason and I always stick to real world scale.

I also rendered one with the Fast Caustics Solver turned off. Sometimes I find this more realistic but less dramatic. I have a space set up here in my studio (a piece of white foamcore and a south light window) that I can lay out a product like this and see how it really looks. This render only took 3 minutes on my workstation.
« Last Edit: 2023-01-26, 17:55:09 by Pepelecrabb »

2023-01-26, 17:45:34
Reply #8

BigAl3D

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50 foot ladder. That's a good one. Clearly not the type of shot that you would consider DoF though, but I see your point. A balance between looks and level of lens distortion.

2023-01-30, 20:16:31
Reply #9

Dean81

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Sorry guys, I thought I had notifications turned on for this post but clearly not.

You both make great points and ones I’d not considered. I’ll change my workflow accordingly from now on and share my results when I get a minute.

Thanks again. Really appreciate you taking the time.

2023-01-31, 17:13:33
Reply #10

BigAl3D

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To Pepelecrabb's point, imagine putting a glass of water outside on an overcast day. No sun. You will see very little to no caustics at all.