Justin Hunt

AO in interiors can add a good feeling of depth and grounding to object, if use subtly. AO can also bring back lost detailing in areas are in deep shadow or are highly reflective.

There are some AO shaders that do colour bleed, but only with one bounce. I did come across a website where there were some XSI shaders that did this, I would have to do a bit of tralling to find to though.

JHV

martin walker

Christopher / Andrew, thanks for your explanation. I was getting the definition of AO confused. I was under the illusion that it was simply a GI calculation using a HDRI or env colour and not lights.

This leads me onto another question.

I render my exterior scenes with a HDRI or just plain (slightly blue) env(skylight) colour . I get little noise and rendering times are very quick....Ive also tried the same for interiors and get decent results.

However if I introduce vray lights, my rendering times increase, I get grainy results....

am I missing something, or is it better to avoid using v-ray lights for a global / ambient illumination, and just stick a direct light in here and there to get some shadows ?

Christopher Nichols

An AO shader that bounces light is not an AO shader. As soon as it bounces light it is GI. As you noted you find that AO adds depth etc... you also mention XSI, MR, etc... All of this points to the fact that you are using AO to add the illusion of GI. Vray can do super high detailed GI with plenty of contrast and detail in all the corners where there is no need to AO. It can do full GI faster then most rendering engines can start to even do AO. The pipeline that you mention Justin starts to breakdown what is great about Vray. That is that it can do all the lighting correctly without the use of an AO hack. In fact, vray even has a "detail enhancer" in the new build that adds an extra amount of detail and humpf to the edges and corners by applying an extra brute force GI (not AO) with a radius falloff to the Irradiance map.

Now... if you want to use an AO style shader to mimic dirt by darkening corner... have at it. But don't confuse it for lighting. Dirt can add depth and grounding as you mentioned, but it is not lighting.

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Christopher P Nichols

Christopher Nichols

If you are using GI to get your ambient light yes... there are time when you want to use and Vray Light in dome light mode with and HDR (in vray 1.5 currently), can work as well but not in the cases you are outlining... meaning they are slow. I outline the techniques you want in my interiors DVD.

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Christopher P Nichols

AJLynn

I usually use a direct or spotlight light source for a sun when needed, though a Vray Light can also be used - there's a section of Chris's exteriors DVD where he does that and it works out well.

Chris- am I remembering wrong or in that DVD do you make a comparison between a GI pass and an AO pass in the highway scene? IIRC it seemed like it could lead to a bit of confusion for people not already familiar with AO vs GI.

Justin Hunt

Chris - I know that AO isn't lighting, I never said it was.

You are also wrong with the AO shader that does colour bleed, it isn't GI. Basically what it is doing is reading the colour of the surfaces the samples are hitting and returning it back to the AO shader. It isn't a lightray, ie the samples do not originate from a light source, it originates from the AO shader. Think of it acting in a similar way a reflection ray works, only not as accurate or time consuming as it only reads the difuse colour of the hit object. I know I havn't explained myself very well, let me find the web site, it explains it much better.

Yes AO is a hack. I have seen plenty of Vray GI render where objects have the apperance of floating, with a little AO - Note I said LITTLE - those objects are grounded. It is just an other way to get detail without the need for lenghy brut force GI calculations.

I have been playing with AO in the reflection slot to give the effect of the reflection changing from sharp to blurry according to the distance of objects to the reflective surface. By using AO distance settings I can control how quickly the transition happens. It does add a heap to the render times but helps eliminate the "blurry all over" look that has been used to death laterly.

JHV

Christopher Nichols

I hear you Justin... but philosophically, completely against you... let me explain. What you are trying to accomplish with AO is what you should be doing with GI... The reason that objects "float" in some Vray renders is that the GI settings are too low. They are not picking up enough samples near the edge. So you suppliment it with some AO. I hate that because it is like you came so close but gave up with AO. Same with the single bounce of light. I think that Vray's GI is plenty fast enough where you don't need to do that, and that you can get a lot more just my increasing your GI quality instead of creating the extra pass. That is why they created that "detail enhancer" setting in the new Vray to get some extra samples right in those areas where and AO shader would get the detail, bit get it correctly with full GI instead of a fak AO. Normally I woudl simply increase the Irradiance map setting, but that allows more freedom. A world where AO is not needed is a better more accurate world of true global illumination, and I will not rest until people realize that....

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Christopher P Nichols

Christopher Nichols

I did... I think I made a similar point that I am making here... am I not?

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Christopher P Nichols

Justin Hunt

I understand your view, I am just giving an other way to "skin a cat"

Although I dont see it as "Giving up on GI" but rather enhancing GI, just in the same way that we enhance our renders in Photoshop, or is that cheating too?

JHV

Christopher Nichols

Yeap... but I say, enhance GI with better GI (higher detail), not with AO. The cost of doing so in Vray would be the same. But that is my philosophy, as an artist. Everyone has their own set of brushes.

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Christopher P Nichols