Reverse Engineering White Balance for existing HDRI maps?

[mdi]

Hi All,

Im working on a project at the moment that inc 1 vray camera, loads of yellow lights and a HDRI image for reflections.

My problem is this, I have WB set to a yellow tone on the Vray camera to counteract the yellow cast from the lights (which works great) but the HDRI map that im using already has the correct WB (ie, grays are gray)..so my yellow WB is making these HDRI go a funky blue.

Iv half way corrected this by changing the HDRI map in photoshop by using "photo filter" set to a yellowish tone (to give the map a yellow tone). But I was wondering if theres a better way to work it out than simple guesswork?

cheers in advance

[werticus]

thats a good point actually, is there a way of excluding the background / environment from wb in the vray camera?

[Clifton Santiago]

In Exposure adjustments in CS3, at the bottom right of the dialog, there is a white (and gray and black) point sampler.

EDIT: Oh, sorry... I misunderstood. That's not the issue.

[mdi]

anyone got a workaround thats works?......anyone?

[vlado]

If you uncheck the "affect background" option in the Color mapping rollout of V-Ray, the white balance of the camera (and its exposure for that matter) will not affect your background.

Best regards,
Vlado

[mdi]

If you uncheck the "affect background" option in the Color mapping rollout of V-Ray, the white balance of the camera (and its exposure for that matter) will not affect your background.

Best regards,
Vlado

Cheers Vlado, but that does not help with reflections though... my reflections are still blue!

any thoughts on a work around?

[ene.xis]

dumb question...but
why are lights yellow if u want them to look white in the first place?
can t u just cc the all thing in post?

[vlado]

You can also simply put the environment map inside an Ouput map and use the color curves to adjust the color of the environment as you wish.

Best regards,
Vlado

[mdi]

dumb question...but
why are lights yellow if u want them to look white in the first place?
can t u just cc the all thing in post?

well, the client wants it set up as a photo shoot they took a few months ago, and the best way I can do this is to make lights yellow and the enviroment blueish as it was at the photoshoot.

Intrestingly I did try it with white lights, but with yellow lights/blue enviroments and with the WB correcting it the over all scene looks pretty close the to photo, but with the white lights it didnt quite look the same.

but the it seems to be working


vlado, cheers, I will try that!

[ene.xis]

that makes sense...i knew it was a dumb question!

[^Lele^]

Or open the HDR in HDRShop (free) and change its white balance automatically or more accurately.
In my experience does a really good job at it.

[jujubee]

Well - for the most accurate colors LWF is recommended, although I've experienced balance issues on exterior setups with the Vray Camera in regards to sky/sun GI.

Seeing that you are relying on a HDR, this should not be a problem.

That being said, if you are not using LWF (this doesn't matter so much), not animating, and working with a HDR in the background - a simple temporary solution would to be do the balance in post on layers. You could set the foreground object to have a MtlID or ObjID then simply balance it there. The only issue I encounter with this post method is aliasing of edges and sometimes opacity goes crazy.

A second method (which I believe used to work - it's been a while) is to put a HDR in a colorcorrect map and I 'think' you could have adjusted the tones/output there as well. But that still may not fix your White Balance problem.

The way you are suggesting is perhaps more accurate from a Max to Vray direct output standpoint (less programs you have to jump through), but the actual tonal change performed by adjusting a HDR's tonal range in Photoshop of HDRShop is highly inaccurate - it almost defeats the purpose of a HDR which is to capture a real-world tonal range related to varying exposure levels. The beauty of a HDR lies within the ability to read various strengths in light exposure (how strong sunlight/GI really is within an image), any color changes would have been a natural by-product.

What you are asking for is a way to directly keep the background HDR excluded (in relations to camera White Balance) and ALSO excluded from reflections. I don't think this is not currently possible as it would require additional programming for a very uncommon situation - having WB exclude or alter reflections. It's a trick that defeats the purpose of a Physical Camera.