Can anyone make an IBL how-to/tutorial?

Oso3D

I'd really like to make good IBL out of HDRs from Carrara, given the ability to make big textures and skies of various kinds that can be used in Daz Studio to provide backdrop and lighting.

As I understand it, something like Picturenaut can take a series of exposures and smoosh them together to get a proper image range to provide good lighting information. But I don't know how to create those 'exposures.' I've tried a bunch of different things, either the image is terrible or the lighting is, as always, almost uniform.

 

Help?

 

mjc1016

In my sig, in the HDRI thread, there's a link to a tutorial, in a general way of doing that...

It's the adaptivesamples link.

Also the thread that steveathome made the Iray hdrs in has some information on how to do it. (also linked to there).

Oso3D

I've seen those links... the adaptivesamples link is great if you have a camera, not so much for Carrera.

Notably, there's no way, that I'm aware of, to set an 'exposure' for a Carrara render. Someone inform me if there is. ;)

 

evilproducer

I think I asked this before in the old forums, and I don't recall the answer, but could you use the Gamma Correction slider in the Render Room set to different values? Maybe start low or at zero and work up?

The other thought would be that if this were an outdoor scene, you could use the Skylight and use the intensity/brightness slider to create your exposure bracket. Come to think of it, that may be a better alternative than gamma correction, because as the amount of gamma correction increases it will balance the shadows and highlights.

Are you wanting the hdr for strictly IBL use, or do you need it visible in the scene as well? If it is visible and supposed to look good, you will need to make it pretty high res, which could make the light calculations take awhile if you use the Skylight. There may be a trick to lower the time it takes to do the light calculations on a large render if you are interested.

There may also be other methods to get your bracketed exposure using your scene lights or maybe fake GI light rigs.

MarkIsSleepy

@MarkBremmer did a tutorial on how to do this - the resulting light was a bit splotchy the one time I tried it, but I think with some work (higher res render, more fake exposures, etc.) it could have been better.

I'll see if I can find the link.

 

EDIT TO ADD: Here it is: http://www.markbremmer.com/3Bpages/darkarts.html - look under "Make HDRI."  Requires Carrara (obviously) and Photoshop the way Mark does it.

DesertDude

A while ago I found a reference to a technique described by Antoine Clappier over at the ghost town Yahoo Group "dazcarrara":

(quoting "dazcarrara" user steven_mcq)

"You can synthesize HDRI output using a set of Carrara renders, as
Antoine described awhile ago, by rendering a set of pictures at
different exposures, controlling the exposure by placing a black
colored plane in front of the camera and stepping through different
alpha percentages for each exposure, like using a neutral density
filter over a photographic camera lens. (Antoine's ingenious idea.)You
would need a program that produced HDRI files from bracketed
exposures, like Photomatix."

I have never tried it myself, but may spark some ideas.

 

 

MarkIsSleepy

DesertDude said:

A while ago I found a reference to a technique described by Antoine Clappier over at the ghost town Yahoo Group "dazcarrara":

(quoting "dazcarrara" user steven_mcq)

"You can synthesize HDRI output using a set of Carrara renders, as
Antoine described awhile ago, by rendering a set of pictures at
different exposures, controlling the exposure by placing a black
colored plane in front of the camera and stepping through different
alpha percentages for each exposure, like using a neutral density
filter over a photographic camera lens. (Antoine's ingenious idea.)You
would need a program that produced HDRI files from bracketed
exposures, like Photomatix."

I have never tried it myself, but may spark some ideas.

 

 

Cool idea.  The advantage of creating your exposures that way is that you could animate the change in alphas and render as a series of images, just letting Carrara run and ending up with a folder full of as many different "exposures" as you wanted.

PhilW

The black colored plane with different alpha percentages is a clever idea. The trick is to capture very bright objects as still white while the rest of the image tends to blackness, this is what will give you the IBL lighting.  For that to work, you will need to make any lights in your scene visible, which they are not usually.  You can use lens flare for example to make the light visible.

Just as an aside, Octane Render can produce spherical images and can save directly to an HDR format (actually EXR, but you can easily convert that in Photoshop to HDR).  It's sun and light sources are generally directly visible too. So you can capture an HDR background image in one pass by using Octane.

And if you are interested in generating your own spheric images for use in backgrounds, I have found an iPhone app called Photo Sphere by Google (I think also available for Android) which does just that and very easy to use, with good results!  These will be standard jpg images though, not HDR, but still good for backgrounds and by combining with a direct light source, will give good results.

evilproducer

Sounds cool Phil. Of course, you could use the resulting spherical render in Carrara as an IBL by enabling Skylight in the render room. It won't look as good as a true HDR, but it can still look very nice.

Oso3D

I'll try the black panel idea. That might produce the range I need. Originally I attempted doing it with gamma but... not very good results.

As for Octane... thaaaat's a lot of money. ;)