Author Topic: Juraj's Renderings thread  (Read 487135 times)

2014-10-24, 22:57:26
Reply #270

tomislavn

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Juraj i did some tests on Hdri you said me to download and its ok it did some sharp shadows my question is if you use always a hdri map always the sun is in the same angle right? if i want another angle i need to find another hdri.. or maybe edit the sun position on the hdri with some program?

Ooooor just rotate the hdr horizontally? :)
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2014-10-24, 23:02:16
Reply #271

Juraj

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Juraj i did some tests on Hdri you said me to download and its ok it did some sharp shadows my question is if you use always a hdri map always the sun is in the same angle right? if i want another angle i need to find another hdri.. or maybe edit the sun position on the hdri with some program?

Exactly, if you need to make the sun position lower or higher, you can move it in photoshop. This can create slightly "impossible" lighting, but it's the same as if you use Sun/Sky and override natural color.

And yes, horizontal is just rotating :- )
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2014-10-24, 23:15:18
Reply #272

demmi

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i am learning from one of the bests one here =)
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2014-10-25, 10:23:17
Reply #273

johan belmans

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Juraj i did some tests on Hdri you said me to download and its ok it did some sharp shadows my question is if you use always a hdri map always the sun is in the same angle right? if i want another angle i need to find another hdri.. or maybe edit the sun position on the hdri with some program?

Hi demmi

if you use the VRAY HDRI map you can rotate the HDRI in different directions. Horizontal is obvious, you can try vertical as well. The last (only slightly), whenever you do not have many clouds in your HDRI and see that the horizon is not showing up. Make sure that it doesn't look odd, I mean clouds running under a strange angle.
Beside this, Cg-source offers HDRI's with different sun height positions (mentioned in the file naming of cg-source). So grab the free once and try out some different HDRI's.

You can paint another sun on your HDRI (in Photoshop 32 bit color space with higher Stops), but I think It is not that easy to mask out the original once, You will end up with some artifacts.
But hey maybe you are beter with Photoshop then I do.

Anyway some more background info about what is good/bad HDRI you can find here http://www.themantissa.net/blog/2014/2/1/the-importance-of-high-quality-hdr

Edit: it seems I missed some posts on the latest page.....

2014-10-25, 12:10:32
Reply #274

Juraj

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Juraj i did some tests on Hdri you said me to download and its ok it did some sharp shadows my question is if you use always a hdri map always the sun is in the same angle right? if i want another angle i need to find another hdri.. or maybe edit the sun position on the hdri with some program?

 you can try vertical as well.
You can paint another sun on your HDRI (in Photoshop 32 bit color space with higher Stops), but I think It is not that easy to mask out the original once, You will end up with some artifacts.
But hey maybe you are beter with Photoshop then I do.

Edit: it seems I missed some posts on the latest page.....

I suggest against vertical rotation, once you have a horizon you're just asking for wrong illumination and reflection.

Moving the Sun doesn't require masking or paiting, you can do it using 'Warp' for example in 5 seconds.
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2014-10-25, 14:43:44
Reply #275

demmi

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Ok i will try next time my painting skills if i can find the right angle in another hdri but tnks for the info belly. One more question about HDRI i have seen too much people using the Vray something to load and control the HDRI and also the corona sun position etc is that really needed? i mean if i am now a Corona user i want to use only Corona stuff to make my renders and what to forget any Vray linked info in fact i do not want the name vray in my scene LOL
If people are using it and i saw some pros using is Corona missing some controls so that people is going this way?
Tnks
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2014-10-26, 02:27:53
Reply #276

Juraj

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I spent some time delving deeper into some stuff and played a bit with Disney's BRDF explorer (and reading fitted MERL data from csail.mit.edi )

So, what is it telling me ? That White (I presume glossy) paint has Albedo as low as <0.4 in linear value ? Seems to me but I am dumb simpleton so perhaps you guys can take a look.

Now if Sergey could finish that SGD plug for Vray for 3dsMax for example I could look directly..but oh well.
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2014-10-26, 15:49:46
Reply #277

Stan_But

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Interesting
Need to find some free time to spent it with the Disney model and with the MERL
Downloaded them a month ago but didn't learn them deeply yet

2014-10-27, 14:30:43
Reply #278

borisquezadaa

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I have downloaded and played with it... but now... where do i put that magic number?.
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2014-10-27, 14:44:13
Reply #279

Juraj

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Heh I was more interested in reading MERL data, as they are fitted from measured source, than how various BRDFs get close. At least I don't know how else to view them :- ).

What I liked about Sergey's SGD BRDF was that it could interpret MERL data and translate directly into usable variables (Diffuse, Specular,etc..) and one could interpolate to other materials based on those 100.
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2014-10-27, 15:27:44
Reply #280

borisquezadaa

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Rigth Click on albedo graph and drag!.
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2014-10-27, 15:34:21
Reply #281

Juraj

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Rigth Click on albedo graph and drag!.

So ? That lets me zoom. And it shows albedo value, quite lower than what I would expect.
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2014-10-27, 15:51:13
Reply #282

Ondra

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So ? That lets me zoom. And it shows albedo value, quite lower than what I would expect.

CG artists have a long tradition of setting albedo unreasonably high because they do not understand what albedo is. As a result, rendertimes are too high and renders look washed out (so people usually end up adding ambient occlusion or decreasing light bounces :D).

I recently made again the mistake of reading up on corona on some other renderers' forums. It is always the same story - if a renderer offers an AO engine, then Corona results look "washed out and unrealistic, with no shadows in corners, probably blurred and faked as much as possible to make it render this fast"
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2014-10-27, 15:59:31
Reply #283

Juraj

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So ? That lets me zoom. And it shows albedo value, quite lower than what I would expect.

CG artists have a long tradition of setting albedo unreasonably high because they do not understand what albedo is. As a result, rendertimes are too high and renders look washed out (so people usually end up adding ambient occlusion or decreasing light bounces :D).

I recently made again the mistake of reading up on corona on some other renderers' forums. It is always the same story - if a renderer offers an AO engine, then Corona results look "washed out and unrealistic, with no shadows in corners, probably blurred and faked as much as possible to make it render this fast"

What :- D ? Would love to read that.

Sure, the days of White=255 are gone, but, that we have the graph literally showing measured White paint to have Albedo as low as 0.35 Linear value at  0 degree incidence. On other hand, some researches like Sebastien Lagarde say almost opposite, that most people author physically based materials to have too low Albedo. I am of course, currently quite in middle, but I am always debating with myself where I should move, higher and lower. And from that point, be consistent among all the materials.

Measured materials are at the moment the closest answer to this question. But is that really so ? I went over 20 materials so far, from chrome to paint, fabrics...and it's always waaaaay darker than what I would image. I'll try to setup some real-world 3D scenario and see.
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2014-10-27, 16:42:22
Reply #284

Ondra

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Ok, if you want some lulz, just search other forums

As for the albedo: do this: Find one material where you are 99% sure you know its true albedo. It can be for example a list of paper (nontranslucent). Place it side by side to real world materials and observe from multiple angles - is the paper whiter? Then its albedo must higher. So you can establish upper/lower bounds on real world albedos.
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