Hdri Dome For Reflections And Ambient Occlusion

[yourdaftpunk]

I'm trying to light a scene with ambient occlussion using the VEX Glob. Illum Light and an HDRI as the environment map. I also want all my objects in the scene that are reflective to reflect that same HDRI. It would also help if I could show the HDRI in the background.

I just moved over from Maya where that ment "click the IBL button and bam: check boxes for visible in reflections, visible in background, Vis. in FG, etc..."

I'm sure the solution is simple, but it keeps eluding me. I get the ambient occ. working, but I don't know how to make a dome that is one sided that will show the HDRI, but pass through the ambient light. Thanks.

[mark]

heres a good technique for reflections:

http://odforce.net/wiki/index.php/CreatingReflectionMaps

cant help with displaying the image in the background though

[sibarrick]

Do you mean display the image in the background for reference? If so do to display options and you can set a background image there. Or you can set up a roto image in the camera object itself under the roto tab.

[anakin78z]

If you want to use a sphere with the hdr on it as a reflection object, but don't want it to render in the scene, make it a 'phantom' object, which means that it'll be included in reflections, but won't render in the image. To do that, go to the render tab of the object and turn on phantom (and set it to 1).

-z

[yourdaftpunk]

Thanks for the prompt replies!

Ok, I set a light up as an environment map per the wiki. Now the hdr reflections look great, the ambient occlusion looks great, but how can I make the hdr map visible in the background, possibly blurred. Is there something like 'phantom' that makes an object visible to the camera, but invisble to the ambient occlusion??

On a side note, where in the render options do I control the number of reflections during raytracing?

-shawn

[sibarrick]

Just set it up in cops as a post composite.

[yourdaftpunk]

Just set it up in cops as a post composite.

19570[/snapback]

I agree. I'm not looking forward to rendering an extra 300 frames, but at least I'll have easy control over the background blur

[yourdaftpunk]

Going the compositing route, I'm now having trouble getting my hdri (in a cross, isixpack...) projected onto a sphere correctly I thought it would have been easy.

[stevenong]

Hi Shawn,

On a side note, where in the render options do I control the number of reflections during raytracing?

19561[/snapback]

Go to the Object's Render tab, turn on "Reflect Bounce" & set it to the number of bounces you want.

With regards to projecting the HDRI onto a sphere, make sure you set the light's Resolution to 768 by 1024 as that is the resolution of the cross map. The Resolution parameter is found under the light's Viewing tab. Also, in the same tab, change the Projection type from "Perspective" to "Polar Panoramic" since the image is essentially a spherical map.

I should make some edits to the odwiki page.

I hope the above helps!

Cheers!

steven

[sibarrick]

It's probably not a "usual" way of doing things, but it's worth noting there is a render cop which would allow you to do the composite and the render all essentially in one hit. The down side as you've spotted is that you can't then change things like the background blur. Just thought you might want to know about it, as it could be useful in other circumstances.

[mark]

With regards to projecting the HDRI onto a sphere, make sure you set the light's Resolution to 768 by 1024 as that is the resolution of the cross map. The Resolution parameter is found under the light's Viewing tab. Also, in the same tab, change the Projection type from "Perspective" to "Polar Panoramic" since the image is essentially a spherical map.

thanks stevenong thats very worthwhile i didnt know this either.

are any changes needed to the GI light, assuming using a .RAT made with isixpack from a veritical cross?

[stevenong]

Hey Mark,

thanks stevenong thats very worthwhile i didnt know this either. 

are any changes needed to the GI light, assuming using a .RAT made with isixpack from a veritical cross?

19593[/snapback]

After posting, I decided I should set up different lights with different resolutions to test this properly & post the results & findings to the odwiki page.

I'll also test whether is it necessary to change the GI light's resolution. Somehow I feel it is not necessary but we'll see.

Cheers!

steven

[mark]

well i dont want to create work for you

the reflections were the big thing.. any changes with the lighting would be fairly subtle so not so urgent

[stevenong]

Hey mark,

After a couple of tests, I can say that HDRI cross maps that have been isixpacked do not require the Light Projection & Resolution parameters to be set. It seems to be taken care of by Mantra.

As for the GI light, more accurately Ambient Occlusion, the light's Projection & Resolution is not required to be changed because Mantra will sample the hemisphere over the point being shaded to compute the incoming "ambient" light.

I guess I don't have to edit the odwiki page.

Cheers!

steven

[mark]

hey steven, i finally got a chance to spend some time on this.

changing the light resolution is the solution to a problem i had that i didnt even know how to begin to explain to ask on the forums

so glad its solved - mmm nice reflections.

cheers

mark

[stevenong]

I'm glad I'm able to help in a very indirect way.

Cheers!

steven

[Allegro]

I've kind of used the file that's in the wiki, but obviously changed the random geo with my model. I also changed the cube to a sphere, and put a longitudinal texture on it. (properly uvmapped so that this would work). This way, I can rotate the sphere, and understand exactly where the highlights etc will be. I map it to the emission values of a supermaterial and just leave it at that.

Is there an advantage to using a saved reflection map with a light? Is it simply to be able to tone down the amount that the reflections appear with the dimmer? I seem to get decent enough results with this method. If I'm animating something, would I need to save out a sequence for my lightmaps?

Is there a way to get at the gamma of an hdr image that I've brought in? I was intending for it to be seen at 2.2 gamma, but the image seems to be displaying at a gamma of 1 in Houdini. Maya also does this, but I can use a gamma adjust node in the hypershade. I assume there must be a gamma node in vops... but I don't know anything about vex, and a supermaterial doesn't appear to have a vopnet.

[edward]

Perhaps someone can enlighten me on this. I've always thought that the proper way with modern computers is:

1. Render your images as 16-bit (or more) with no gamma correction (ie. linear light). It must be 16-bits or more to avoid precision loss.

2. View your images with whatever gamma your display device you're using as you're lighting. In mplay, this is easy, just change the display gamma to 2.2 (or whatever your display device uses) if you don't have some OS thing going on already (like that PhotoShop Gamma thing, the gamma slider in the nVidia display drivers, etc).

3. Apply gamma for your specific output device in the compositor when you're done. This is easily done in COPs with the Gamma COP.

So to me, applying gamma correction in the shader just seems the wrong thing to do?

In anycase, if you must apply gamma in your VOP net, I think you can just use a Power VOP with the constant set to 1/gamma where gamma is your output device gamma (eg. 2.2).

[Allegro]

Perhaps someone can enlighten me on this. I've always thought that the proper way with modern computers is:

1. Render your images as 16-bit (or more) with no gamma correction (ie. linear light). It must be 16-bits or more to avoid precision loss.

2. View your images with whatever gamma your display device you're using as you're lighting. In mplay, this is easy, just change the display gamma to 2.2 (or whatever your display device uses) if you don't have some OS thing going on already (like that PhotoShop Gamma thing, the gamma slider in the nVidia display drivers, etc).

3. Apply gamma for your specific output device in the compositor when you're done. This is easily done in COPs with the Gamma COP.

So to me, applying gamma correction in the shader just seems the wrong thing to do?

In anycase, if you must apply gamma in your VOP net, I think you can just use a Power VOP with the constant set to 1/gamma where gamma is your output device gamma (eg. 2.2).

Haha, thanks I was about to reference this post in the other hdr topic. I guess I'll keep it all in this one. As you can see, I've ended up using just the sphere. I'm really new to the world of hdr, and had never really been aware of gamma until a couple weeks ago... so I compensated in Maya with my other scenes with the gamma correct node in my shader. I realized about 10 mintues after this post that you can change the gamma output in ROPs. That made it look the way I was expecting it to.

I've got to put finishing touches on the cotton crop (same shot)tomorrow, and then figure out some particle pesticide spray, but this is the shot I'm working on.

I really wasn't having any luck with the .rat image in the light... I couldn't figure out how to get the light source where I wanted it.

Edited April 4, 2007 by Allegro