Corners Don't Look Like That: Regarding (Screenspace) Ambient Occlusion

[vlado]

Maybe in interesting read for AO lovers

http://nothings.org/gamedev/ssao/

Even though it's written from a games perspective, all the points are perfectly valid for true AO as well.

Best regards,
Vlado

[instinct]

Maybe in interesting read for AO lovers

http://nothings.org/gamedev/ssao/

Even though it's written from a games perspective, all the points are perfectly valid for true AO as well.

Best regards,
Vlado

Thank you. And in addition if you take a look at outside shots AO needs to be applied to AMBIENT only areas. Hence the name. Whereas it is often applied to the whole image. Which makes VRayDIRT the far more fitting name

Regards,
Thorsten

[trixian]

I find the author of that article to be slightly confused by what is going on in his images. He also could use a better set of images for this topic. I'm pretty sure there are some scientific papers on this with better illustrations, and more importantly, better data for measuring.
In our real physical world, there is no ambient, diffuse or specular. These are simplistic concepts created by man to more easily describe reality, and this "AO" would even encompass "lack of bounce light" from other surfaces, aka GI in our field.
While I completely agree that SSAO/AO is used horrendously in a lot of cases, this does not invalidate the need for it, especially when done properly.
In addition, I will claim that the optical effect known as AO does indeed happen everywhere, even in areas otherwise lit by other lightsources, but you will have problems seeing it as the light is inherently additive (no negative lights in my world at least). You can easily see the slight "AO" in otherwise lit areas with your bare eyes in the right conditions (i.e not too much contrast between light and dark). This is also visible on photos, but would be harder to detect because of the limited range in photos.
One really obvious way is to make your own hdr image, of something with a varying frequency of shapes and sizes, and preferably a mixed lighting condition (magic hour comes to mind). Expose this up and down and see the incredible persistence of shadows in all areas as you expose up. You should also be able to detect the ever so slight "AO" even in lit areas if everything is balanced.
We only seem to experience the "lack of AO" when looking at values too close together for our perception or cameras value range, but they are still there.

Anyway, might be this post was pointless, as there is a difference between what is objectively real and what is percieved, but it just seemed strange to read those comments above.

[super gnu]

i guess most people already realise that ao isnt physically correct. however for me at least, what is physically correct is pretty irrelevant. its what looks good. if used subtly, ao is great for providing definition to forms and sharpening up blurry GI. and besides, as the author of that article notes. it does -look- like there is ao in most of his samples. and i can definitely see it in the corner of my room

[vlado]

it does -look- like there is ao in most of his samples. and i can definitely see it in the corner of my room

Dirt does tend to accumulate in corners, that's for sure

Best regards,
Vlado

[super gnu]

freshly painted room

[Neilg]

Thank you. And in addition if you take a look at outside shots AO needs to be applied to AMBIENT only areas. Hence the name. Whereas it is often applied to the whole image. Which makes VRayDIRT the far more fitting name

Regards,
Thorsten

Exactly why I use the raw shadow pass as a mask

[Macker]

Exactly why I use the raw shadow pass as a mask

That's a really good idea.

[mcnamex]

when can we see the update ao engine from chaos

[instinct]

when can we see the update ao engine from chaos

The point of the article is that AO does not exist as it is usually used...so what would you want chaos to change?

[raymarcher]

Just aply the dirtshader in the vray ambient light and you have setup yourself a "correct" occlusion of ambient light.

[instinct]

Just aply the dirtshader in the vray ambient light and you have setup yourself a "correct" occlusion of ambient light.

Not for post tho, which is what AO is often used. I KNOW that you CAN setup AO okay by applying it to ambient areas only, but it is still off, and it is often not beeing done. Besides i don't think the whole concept
applies all that well to interiors...because all ambience is occluded no? :P

[grantwarwick]

Never use AO.
As far as I'm concerned that shit died to me years ago.

[mcnamex]

Never use AO.
As far as I'm concerned that shit died to me years ago.

BF all the way

[joconnell]

Never use AO.
As far as I'm concerned that shit died to me years ago.

Ah the compers like it