Rendering hdri with vray

[flipside]

Hi,

I'm making some hdri's myself, and I have a big problem.

I put together LDR images with HDR shop. But hdr shop works in gamma 2.2 and vray loads hdri's at gamma 1.0. So every hdri looks too contrasted in max.

Take a look here:
http://hdri.cgtechniques.com/~blochi1/show.php?id=326

That's my problem, and this guy somehow found a solution.

Editing the original LDR images doesn't work. I need to simply render out the hdri set as a background image with gamma set to 2.2 and save this image as my new hdri with gamma 2.2 baked in. But this seems to be impossible! You need the hdri loader from brazil to be able to save to hdri, but when I use the good options for it, the gamma adjustment from max is ignored.

Did anyone else ever found a way to simply edit the gamma of a hdri???

Even better would be if Vlado could add an option to the vrayhdri map to adjust the gamma... please

Note that almost every hdri you can find on the net will display incorrect in max as it opens at gamma 1.0.

[vlado]

Ideally, you should apply Gamma not to the HDRI image itself, but to the final rendered result which uses this image. This is because the Gamma correction is purely for viewing purposes. Otherwise, if you apply gamma to both the rendered result and the HDRI image, the HDRI will be corrected twice, which is probably not what you want.

To camma-correct the final rendered result, use the Gamma correction color mapping mode in VRay (where you should set the Bright multiplier to one over the gamma value, for gamma 2.2 this would be about 0.45).

Best regards,
Vlado

[flipside]

Hi Vlado,

I remember this gamma thing from another thread about linear space etc... but never understood it fully I guess.

I found a simple solution for adjusting gamma (and more) of the hdri, with the color correct plugin you can find here:
http://www.cuneytozdas.com/software/3dsmax/#HDRI

So I tried rendering a scene with the gamma corrected hdri and without gamma correcting the hdri but using the gamma control like you suggested.

Gamma correction to hdri (with color correct plugin, this is the same as actually editing the hdri, I tried it with a map someone converted to gamma 2.2 for me):



gamma correction to rendered image with default hdri:



Shouldn't these two show the same result?

here's the scene without any gamma correction (reflections look nice on the blue teapot, but they are too dark on the metal one compared to the real environment)


And one of the original LDR pics I used to create the hdri:



Thanks,

wouter

[Dschaga]

you can try this:



it's nothing else then a pseudo inputgamma for a map ..and it works very nice for me, even if it's not really accurate

[jujubee]

Looks like you partially solved your problem...:

http://www.ict.usc.edu/graphics/HDRS...asc&highlight=

Also, I kinda wonder what the gamme defaults to if you use Mkhdr instead of the GUI assemble?:

http://www.debevec.org/FiatLux/mkhdr/

...or is the problem mainly during the process of applying the camera curve, cropping, transforming, and saving out?

[flipside]

yep they helped me out yesterday night, that's where I got the link to the color correct plugin from

[jujubee]

oops- just added/edited to my own post a couple of questions.

[flipside]

MKhdr was way to technical for me, I didn't try it any further.

The camera curve is something else, I don't think it has anything to with the actual gamma baked into the generated hdri. I tried messing it up to get a different gamma in the hdri result, without any luck.

I think you will get the same result with mkhdr as with hdr shop, regarding the gamma.

It's weird, if I use the gamma corrected hdri for lighting too, it doesn't look correct, lighting gets way too diffuse, the direction of strong light sources fades away a lot. I get best results with the standard hdri in the skylight slot, and the gamma adjsuted one in the reflection slot...

[jujubee]

Even easier solution to all this, download the trial...:

http://www.chaoticdimension.com/foru...?p=90574#90574