2
$\begingroup$

This is not a duplicate of the tricky glass shader question.1 The tricky glass shader does not handle the features of this scene.

I've been trying to render an image to match the glass in the original photograph and failing. I've tried materials based on using the "tricky glass" glass and transparency nodes as well as materials based on using the refraction and glossy nodes. I've tried using Fresnel input and light paths to control mixes. I can get close with some fairly complex shaders but none of them do the job.

Below is the original photographoriginal photograph and a recent render most recent render.

I am aware of the modeling and lighting differences and haven't added the dirt and smudge textures yet. Taking those into account, there is still room for improvement.

The two problems that I am concentrating on right now:

Why is the glass so dark compared to the lazy susan?

How do I model reflections coming from the inside of the back face of the glass?

I can't share the original blend file because of licensing restrictions, but I have stripped out the licensed bits and can share that blend file.

$\endgroup$
  • 2
    $\begingroup$ Don't use clamp direct. If you set it to a value of 1 all light values higher than one will be clamped, effectively making your lights dimmer and useless. $\endgroup$ – cegaton Feb 17 '18 at 4:13
  • 1
    $\begingroup$ Possible duplicate of: blender.stackexchange.com/questions/45195/… $\endgroup$ – cegaton Feb 17 '18 at 4:14
  • $\begingroup$ You need more lights and more "fill" coming from the left (The dark shadow on your table is a hint). And a light in the front to illuminate the logo. $\endgroup$ – Dontwalk Feb 17 '18 at 16:37
  • $\begingroup$ Also, your glass needs to be thicker. Especially at the base. This will help with the reflections. $\endgroup$ – Dontwalk Feb 17 '18 at 16:43
6
$\begingroup$

Don't use Clamping (especially with such a low value of 1). It prevents the lights from being simulated realistically in something as complex as glass. Turning on Caustics also helps.

Here are some render comparison:

enter image description here

To me, the glass material is unnecessarily complex, unless you have a good reason to use it (for dispersion, etc), I suggest you looking into the Principled Shader. With one shader, we can achieve even better caustics and faster renders.

enter image description here

$\endgroup$
  • $\begingroup$ !New render with a !simpler glass material, from Stephen Woods on the facebook blender nodes page. Clamping is still set to 1, and is pretty obviously not the issue. Caustics are back on. I was avoiding them to avoid having to increase the render time. Without caustics, 500 samples works, with, 5000 still leaves some noise. $\endgroup$ – Marty Fouts Feb 17 '18 at 21:54
0
$\begingroup$

It turns out the problem was the reflectivity of the glass. Stephen Woods on a Facebook group pointed out that I could mix Layer Weight Fresnel and facing values to use as the mix fac for mixing a refraction node with a glossy node. All I had to do was tune blend factors in his simple glass material. Well that and up the render samples by a factor of eight.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.