Noisy, Grainy shadows with plastic - Not so urgent anymore

[timbudtwo]

I apologize in advance for the urgency.

I have used translucent plastic in the past, but I am trying to emulate a milk bottle material now. Actually, I am trying to emulate injection molded recycled milk bottles like this: http://www.greentoys.com/sites/default/files/styles/uc_product_full/public/Race%20Car%20Red.jpg

That company, Green Toys, uses recycled HDPE bottles for all of their toys.

Anyway, my renders are coming out like crap and I am not sure why. I have tried using the stock materials and custom materials and both are giving me really bad shadows. The first is with all stock materials, the startup environment, and I rendered it with full simulation, 32 samples at 300dpi. The second is a dosch environment, with rough plastic with a little bit of the cloud bump added it to, also rendered at 32 samples and full simulation and 300dpi.

What am I missing?

[timbudtwo]

Rotating the environment improved the conditions, but I still needed to wait for over 100 passes for the shadows to clear and thats just crazy.

I switched to a low-bump mold tech for the body and wheels, and rough plastic for the tires.

Still suffering from shadow issues

[LayC42]

Hello T_T student.

First thing is about the lighting preset.
"product" should work fine in this case. You can also work with a custom setting like:
Ray bounces about 10-20
Indirect reflection 2-10
global illumination on
no caustics

second thing is about the material:
I prefer a plastic (advanced) where I can play with the transparency parameter and both transmission passes.

There is a very good webinar from Richard Funnel in the learning section showing nearly everything for transparent plastic.

Hope that helps

[Esben Oxholm]

In my experience it is not uncommon to have to go with 200-300 samples to get clean shadows. Especially with semitransparent materials.

[timbudtwo]

Yeah, that is what I just resigned to do this afternoon. Fortunately most of them turned out well enough for my liking and into the portfolio they go!

[richardfunnell]

One thing that went unmentioned is increasing your material samples; you can do this for most materials (but not basic Plastic) in order to improve the material quality without increasing your global parameters. I don't mean to hijack your thread, but it's pretty relevant for your problem.

In the attached rendering & KSP, the materials are all the same: Plastic (Transparent) plus .1 roughness, EXCEPT the material samples are different on each part. You can increase or decrease the material samples, which overrides your global setting for that material. This means you can decrease your global samples while only increasing it on materials that need it.
The image was only rendered at 9 samples using Max Samples, but you can see the quality difference between the different materials. In order to improve the results of your materials without increasing every slider, try increasing the materials that need it the most.

Most materials have a default sample value of 9, however advanced materials like Solid Glass & Translucent will have their own higher sample value as needed. I usually set material samples at 16 for my "nice" renderings, or higher when using more advanced materials (24 or 32).

Also, that's a great model I hope this helps!

[timbudtwo]

No hijacking happened! This is great info. I have found the documentation of keyshot to be pretty lacking - you really just need to know how light works REALLY well to understand what the software is trying to do. I did end up turning the samples up to 32 from 9, but I still had to get about 150 passes before the shadows cleared up and looked smooth.

Thanks for the compliment. My school has us build everything in solidworks; there was lots of screaming involved on that one.