Author Topic: Juraj's Renderings thread  (Read 329024 times)

2014-08-14, 16:51:01
Reply #225

romullus

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Does it have multiple material ID's? If so, it can be this bug: https://corona-renderer.com/forum/index.php/topic,4943.0.html


{{Romullus: should I render against Black only in directly visible and refraction ? Or all 3 ? Maybe the reflectivity override to black is causing what seems like too much reflective glass; off-topic}}
Lot of thanks for feedback guys. I'll get back

Sorry, couln't say, i don't do comping much. But for glass i go no more than 0.25-0.3 reflectivity. I find it more realistic than usual 0.9-1.0
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2014-08-14, 17:10:06
Reply #226

Juraj Talcik

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The super-reflectivness is because I did black override in reflection too, without it looks correct :- ). It's my mistake.

I disagree with the lower reflectivity, real glass used in windows (without any foil on top), the regular soda-lime, is 8perc. reflective which in the CGI model like Corona/Vray/Scanline/etc.. is represented oppositely,
full 1.0 (but almost everything is 1 at grazing...) at grazing/90 angle (and mostly 0.04 at 0) with fresnel of ~1.5, so the average will be the same.

http://glassproperties.com/refractive_index/ general properties

http://refractiveindex.info/?shelf=glass&book=soda-lime&page=Rubin-clear  //exact sola lime glass properties and its reflective curve


I will check those IDs though.
« Last Edit: 2014-08-14, 17:16:02 by Juraj_Talcik »
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2014-08-14, 17:39:17
Reply #227

Juraj Talcik

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FOUND IT !

It was indeed multi-texture bug. But the bug remains even after updating to Multitexture 2. It's not affected by DR, the bug manifests even if single machine does it.

Should I send the scene to you Keymaster ? Once you have time, I can live without MT for now.
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2014-08-14, 20:12:05
Reply #228

romullus

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I don't think it's related to multi-texture specifically, but to multi materials and refraction overall.

The super-reflectivness is because I did black override in reflection too, without it looks correct :- ). It's my mistake.

I disagree with the lower reflectivity, real glass used in windows (without any foil on top), the regular soda-lime, is 8perc. reflective which in the CGI model like Corona/Vray/Scanline/etc.. is represented oppositely,
full 1.0 (but almost everything is 1 at grazing...) at grazing/90 angle (and mostly 0.04 at 0) with fresnel of ~1.5, so the average will be the same.

http://glassproperties.com/refractive_index/ general properties

http://refractiveindex.info/?shelf=glass&book=soda-lime&page=Rubin-clear  //exact sola lime glass properties and its reflective curve


I will check those IDs though.


Is this means that reflection level value in CoronaMtl defines reflectivity strength at grazing angle rather than at 0°?
I don't have deep knowledge in materials, but i certainly willing to learn more. I've learn from here that almost all dielectrics should use about 0.2-0.3 reflectivity and metals 0.6-1.0, so i tend to stick to that rule. I would love to hear your opinion, because you know what you're talking.
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2014-08-14, 20:36:27
Reply #229

Juraj Talcik

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specular reflectance of the material which is the value of Fresnel reflectance at 0° (reflectance at normal incidence) : F(0^{\circ})  [1]. The term F(0^{\circ})  is what we call specular color for our physically based shading model.


They do define all this reflectivity based on normal incidence, but not directly from those overall albedo values, as those include both diffuse and specular reflectivity.
Up to this time, I am still confused how to directly translate their data into our model, and closest and easiest is just the reflective curve for materials where that is available. But beyond that, hmm.
And that curve always goes from [specular reflectivity at 0] to 1 [at 90 angle]. When averaged from all angles + diffuse reflectivity= we get the overall value written everywhere(ie. snow 90perc.,etc..).
But we can't drop that value into our specular or diffuse slot as I've seen people doing. It's useless for us.

What does specular value in Corona/Vray/etc.. correspond to ? I don't know. If it's white[=1], and IOR of ~1.6 is used, it's almost the same as reflective curve of average dielectric material like plastic [which would have 0=0.04 and 90=1],
so maybe it's only some arbitrary number that get multiplied by the IOR curve, maybe it is 90 angle value, which then shouldn't really be moved for non-metals as long as IOR is used (i.e, it should imho always be 1=white).

But please don' take me literally, I am only curious, and dumb at that :- ) It's all my limited interpretation and I do feel lost like everyone else. I just don't like "eye-balling" and "do it like artist" answers.


Well, regarding bug and multi-material, refraction: The model of glass outside is simple box, edit poly with chamfer, single ID=1. The glass material is single material, it's not in multi-material.
The floor had multi-texture applied. Once I swapped single thing, the floor to single texture, the bug was gone, shadows were transparent again, and all those odd shadings were gone too.

This leads me it's more problem with the multi-texture somehow ? I don't really know what's happening.

« Last Edit: 2014-08-14, 20:56:18 by Juraj_Talcik »
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2014-08-14, 20:53:30
Reply #230

romullus

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So maybe it's yet another bug? i'll try to play with multi-texture map, then and see if i can replicate it.
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2014-09-11, 15:24:56
Reply #231

Juraj Talcik

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Hi guys, because most questions I get on email are regarding lighting, I share 3 pdfs out of my recent presentation. They're basic because I mostly rely on talking, but maybe you're interested in browsing through them before
I compile it into something more complex and add more of them.
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2014-09-11, 16:36:23
Reply #232

CiroC

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Thanks for sharing. I often struggle with HDRI, but I don't if it is related to the quality of the HDRI or the camera settings I am using.

2014-09-11, 16:43:02
Reply #233

Juraj Talcik

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Quality of HDRi can be actually quite crucial. Lot of them just aren't dynamic enough, and have quite strong color cast that wouldn't be there in real life, producing too 'fairy-taily' effect, dimmed reflections,etc..
There is only one source I stand behind, CG-Source. All other are (for archviz, I am not talking high-end automotive ones like Moofe, different league) subpar.

You can still use those to great result, but it will strongly depend and make your life more complicated. Or you can embrace the unique look. I don't.
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2014-09-11, 17:01:27
Reply #234

CiroC

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Definitely with some if not most of the HDRIs, we have to remove that blueish look, like Grant shows in one of his videos. I really need to give a go with CG-Source although they need to add a few more HDRI to their collection.

Usually what happens when I am using HDRI is trying to get the "correct" camera settings in order to get good light without burnt areas. And then is when I start to think that: a) I am doing something wrong or b) the HDRI's quality is not great. How do you tackle the camera settings?

I find interesting that you mention the need to have a spherical HDRI. If you have an HDRI that is only hemispherical do you use a reflective plane?

Thanks again for sharing your insight


2014-09-11, 21:45:12
Reply #236

CiroC

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Hi Cyrus3v

maybe this article can be of any help
http://www.themantissa.net/blog/2014/2/1/the-importance-of-high-quality-hdr

Thanks for sharing. There is a massive difference between a good and a less good HDRI. It is just a shame that we cannot check the HDRI's quality before buying it.

Thanks for your time

2014-09-12, 00:23:10
Reply #237

Marvey

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Hi Juraj

Is interesting you told it is better to use a spherical HDRI and avoid a hemispherical, all the hdris i used from the past till the present including cgsource and peter g. all of them have the black part in the buttom.. since it is better the spherical, and guys like peter g. and cgsource who are experient ppl why they sell this hdris with black parts? well you have any technic to fix it?
regards

2014-09-12, 00:31:13
Reply #238

Juraj Talcik

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If you create full CGI environment around your scene (like grassfield with Trees and other stuff covering horizon) than hemispherical is totally fine.
The problem is when it is used directly for any type of scene, which people often do, where that black part will create issues with lighting and reflection.
Something needs to be done to some extent to correct it (for example, make the black grey, or put infinite plane in Vray,etc.. those kind of solutions), but it will still have some issues because some of these HDRi can have cropped and rescaled part above horizon,
so the intensity there isn't that correct.

In Archviz we generally use HDRi differently than rest of the industry, as we just want "nice sky" out of it to do the lighting. Often in 99perc. of case, there is no compositing, so fitting spherical map isn't required.
And horizon could actually detract unless it was shot far out, so we would always have to find spherical one with matching perspective distance to our current scene. Last, high quality spherical HDRi for automotive industry (like Moofe), are superbly expensive.

But I can imagine someone to shoot and sell proper spherical HDRi for archviz, high dynamic range (16+ stops), hi-res (16k+ px), and with open-wide environment (cityscape from skyscrapper, wide open beach/ocean panorama/,grassfield shot from window height,etc..), but something like that would probably be bit more expensive than people are used to, and outside of few very good professionals, not many people know how to. Really, CG-Source is 10 levels higher than all the others together.

Some old quick example of "quick fix". It's blurred btw because I wanted softer shadows, not because of "sIBL" ! The grey bellow horizon provides some additional light to scene and specular don't show sharp line.


« Last Edit: 2014-09-12, 00:44:27 by Juraj_Talcik »
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2014-09-12, 02:44:00
Reply #239

Marvey

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very nice info Juraj, thanks for the help!
regards