what is spectral rendering exactly?

ed3D

+ interresting subject   _``~...

JasonWNalley

Sorry to re-hash a dead thread, but Spectral has definitely done something to the lighting and I am trying to figure out how to fix it.  I rendered a scene without it, and had nice defined shadows, now that it's on, the scene lighting is way dimmer, and there are nearly no shadows... I also had to turn the environment intensity from 1 up to 10 just to get a similar "brightness" level out of it.  Does anyone know what's going on?  I've got spectral on, Faithful, CIE1964... (I've tried Environment Intensity 1, 2, 5, and 10.  1 is to dim, so is 2, 5 brightens some things up still no real shadows, and 10 brings the foreground close to how it used to look but blows out the background.  I also tried lighting resolution from 512, 2048, 4096 and 9072, none of which did much for the shadows...)

emoryahlberg

JasonWNalley said:

Sorry to re-hash a dead thread, but Spectral has definitely done something to the lighting and I am trying to figure out how to fix it.  I rendered a scene without it, and had nice defined shadows, now that it's on, the scene lighting is way dimmer, and there are nearly no shadows... I also had to turn the environment intensity from 1 up to 10 just to get a similar "brightness" level out of it.  Does anyone know what's going on?  I've got spectral on, Faithful, CIE1964... (I've tried Environment Intensity 1, 2, 5, and 10.  1 is to dim, so is 2, 5 brightens some things up still no real shadows, and 10 brings the foreground close to how it used to look but blows out the background.  I also tried lighting resolution from 512, 2048, 4096 and 9072, none of which did much for the shadows...)

Hm. I've never had trouble with Faithful. That seems to always use the same lighting, whereas "Natural" can make some lights appear about 75% dimmer.

margrave

Spectral Rendering is like turning an 8-bit image into a 16-bit image. If your color values were at 255, that's the max for an 8-bit image. If you expand the range to 16-bits, your color values become 255 out of 65,536.

barbult

If you were using sun-sky lighting (no HDRI image loaded) and saved the scene, when you reopen the scene, Daz Studio 4.15 will load the default Ruins HDRI image. That bug has nothing to do with spectral rendering, but it may be what happened to you to change your light and shadow strength. Delete that HDRI image from the Render Settings Environment tab.

JasonWNalley

@barbult thank you! That was exactly the problem!  I was scratching my head.

barbult

JasonWNalley said:

@barbult thank you! That was exactly the problem!  I was scratching my head.

I'm glad it helped you. It is a real annoying bug.

zwalraven

I had a situation were I tested the same render twice with Spectral Rendering/Faithful/cie 1931 ON and with Spectral Rendering OFF completely. The render with it OFF actually took 1.5 minutes longer. From everything I've read, and this threat. This is not supposed to be the case. Can some explain why this could possibly happen? Are there certain lighitng conditions etc... I guess what I'm getting at is, would this be the exceptiong to the rule? Thanks

Leonides02

It is kind of a crapshoot. Sometimes spectral shortens the render time, sometimes it is longer.

But the point of spectral is more accurate light, not render time reduction.

karlsfriend_f7ccaca9e2

peluprogrammer_94060e24b0 said:

I just notice an improvement if i use Spectral Rendering. I had these strange fireflies on my scene that disappeared when i use Spectral Rendering. Same rendering time -- 2 min 100 iterations. Fireflies start to appear around character nails after 50th iteration.

This is a great example.  Thank you.

karlsfriend_f7ccaca9e2

prixat said:

Refraction and caustics is still controlled by the material IOR (and Abbe number). It's not clear if spectral rendering has been implimented any further than just surfaces, reflections and indirect.

The Observer Intent seems to work as expected:
CIE 1931, reduces blue significantly and adds a bit of green and a bit more red.
CIE 1964, all the colours get a tiny boost, but blue is boosted less than green which is less than red.

Can you confirm what I see, (I've been looking at these images too long) 1931 has made the floor more purple, 1964 has made the whole image a bit brighter .

This is a good example.  The problem for me was it was difficult to see the difference from 3 different examples that were so far apart.  I hope you don't mind but I used Photoshop to cut them closer together where I can really see the difference.

 

 

prixat

You may find this little free program from nVidia useful for comparing images, nVidia ICAT:

https://www.nvidia.com/en-gb/geforce/technologies/icat/

 

Spectral Rendering has moved on quite a bit with a choice of extended colourspaces added to the spectral conversion.

algovincian

prixat said:

You may find this little free program from nVidia useful for comparing images, nVidia ICAT:

https://www.nvidia.com/en-gb/geforce/technologies/icat/

 

Spectral Rendering has moved on quite a bit with a choice of extended colourspaces added to the spectral conversion.

Thank you for linking that utility, @prixat. Very useful and much appreciated - cheers!

- Greg

karlsfriend_f7ccaca9e2

prixat said:

You may find this little free program from nVidia useful for comparing images, nVidia ICAT:

https://www.nvidia.com/en-gb/geforce/technologies/icat/

 

Spectral Rendering has moved on quite a bit with a choice of extended colourspaces added to the spectral conversion.

 

Thank you for that.  It will help in a lot of ways.

This community is so smart!

Padone

Spectral rendering is a different way to compute light. This allows for more physics effects than raytracing. Unfortunately spectral rendering also requires spectral materials to be defined and this is not the case with most rendering engines, including iray. So a conversion is done on raytracing materials and this is where the spectral options come in. Specifically faithful + rec709 + cie1931 is what to use for daz assets and are the default values. The other color spaces are needed if you define textures in a space different from srgb that's not the case for daz assets.

https://en.wikipedia.org/wiki/Spectral_rendering

https://docs.omniverse.nvidia.com/prod_materials-and-rendering/prod_materials-and-rendering/render-settings_iray.html

Dpiximaj

@Padone... interesting... did you ever port to 4.20? Off beta?

alan bard newcomer

render the scene in both modes and then blend layers in photoshop or your equivelent]

 

Padone

@Dpiximaj I use 4.20 as beta because there's a difference on some material features. So old assets will work fine in 4.15, unless they're updated for 4.20.