Ambient Occlusion into a mirror

[derekcerciello]

Hello all,

 

I'm trying to get some sort of ambient occlusion into my mirror material.

I'm currently only lighting my scene with 1 omni light which is only for ambient Light and also have mr sun and sky.

 

Is there any way to do this in a separate pass?

 

This is what im getting currently.

(Its a spherical, so just rotate the image to see the mirror)

 

http://cghdemos.azurewebsites.net/Bathroom1/Bathroom.html

 

Thanks in advance

[Francisco Penaloza]

I don't think it can be done a separated pass, did you try to use the AO within the material it self?

[SgWRX]

i created a white door with a mirrored wall next to it both sitting on a plane. i aimed the camera into the corner where the door and mirrored wall almost intersect.

 

i used 1 mr omni light only. placed up and almost where the camera point of view was.

 

for the door and the floor i used a default arch&design material with diffuse color set to rgb .5, .5, .5. in the special effects i put the check in the box for ambient occlusion, set the max distance to 2ft 8in (arbitrary). i set the custom ambient light color to pure white and shadow color to pure black.

 

i rendered a mr A&D Raw Ambient Occlusion pass and mr A&D Output Reflections pass. the AO pass looked like i expected, the mirror had no AO. the floor under the mirror and the door had AO. the reflection pass had only the mirror and both the door and the mirror had AO where it was reflected in the mirror.

 

i think that the AO pass was a little "stronger" than the beauty pass that rendered along with the two passes. and of course when turning off AO in the A&D material in the door and floor, both passes did not have any AO.

 

so i think you might be able to do it with a reflection pass.

 

---photometric light with mr photographic exposure control---

 

i deleted the mr omni light and replaced it with a default photometric light, set to emit light from a point. also left the default intensity of 1500cd. things were not look right as expected. so i tuned the mr photographic exposure control to an EV of 7.5. then as expected things still didn't look right, so in the physical scale for the mr photo exp control, i changed from physical units to unitless and left it at 1500.0. re-rendered and everything looked better, but the reflections pass was a little dark, showing a medium grey rather than white for the reflected door and floor. in the render elements for the reflections pass, i scrolled down and set the multiplier to 2.0 instead of default 1.0. that made things look nice again.

[derekcerciello]

Thank you for your replies.

 

I tried to use the technique that sgWRX used, but i couldn't seem to get the same results.

I tried it multiple times in my scene and had no luck.

 

Perhaps I will try it on a smaller scale when I have time.

It may be because I am using the material override to generate my AO pass initially?

I ddid however turn it off when i tried the method above, so im pretty lost to be honest.

[SgWRX]

hi derek. yep from my test/steps above doing an AO pass or using it as the material override won't give the AO in the reflection. it's when i used AO built into the A&D material that the reflection pass in render elements showed reflected objects with AO.

 

if you want, you could zip up your scene or parts of your scene with assets and post it up here and i could take a look at it.

[SgWRX]

derek, i think i misunderstood what you were going for... but i think the reflection pass still could be your thing. instead of getting 1 set of renders with AO override material to put on top of your beauty render, you'd have to do two. 1 AO override, then one that renders just a reflection pass with AO applied to all the objects in your scene EXCEPT the mirrors - they'd stil lhave to have the reflective material. so in your case, maybe just apply the A&D material with the built in AO -or- apply the AO override material to just the door and frame, then render out again but use the reflection pass. so then you'd have your 1 rendered image, 1 AO override image to multiply on top of that, and 1 reflection pass to either "add" or "screen" or "multiply" in there.

[derekcerciello]

Yes this is exactly what Im trying to do.

 

I did try it as you explained, but can only seem to get a white mirror in my reflection pass.

Maybe I could email you my test file to take a look at? I dont seem to know what Im doing wrong.

[SkylineArch]

I haven't used mentalray in years so I can't remember how compatible this would be, but in Vray you could render an AO pass by placing a dirt map in the diffuse of a vray light material, and place than on every object (override), except the mirror, leave that as a 100% reflective mirror shader.

 

Hide all other lights and turn off or adjust camera exposure as needed, or in Photoshop, take your AO "pass" and adjust the levels by picking a white point to set it back to pure white if your exposure is a little off.

 

As a side note, I put an RGB Multiply in the diffuse of the light material, and then put 2 dirt maps in there, one for a smaller distance, like 2", the other about 24". For exteriors I do larger distances. you can make the black color more gray to tone one of the 2 down if you want. set the samples to 16+ to get rid of the grain.

 

In my experience, doing a separate AO render give you much better results and adjustment than adding AO in the rendering or shaders, it will also reduce render times since the AO light material renders pretty quick.