How good is Terragen for creating HDRI environment textures?

[reck]

I'm wondering how good 360 degree HDRI skies rendered in Terragen are compared to traditional photo based HDRI's?

One of the metrics used when comparing the quality of HDRI's is how wide the dynamic range is or how many EV's it uses. The photo based HDRI's I use at the moment are 26 EV's, how would an image coming out of Terragen compare to this? 

I'm looking to create sky HDRI's for use in Blender for environmental lighting.

Thanks

[paq]

I would say Terragen will produce the highest dynamic you can store in a 32bitts float image.

I just did a test using a sun strength of 0.0001 (instead of the '5' default) and I could re-expose the image in photoshop, pushing the exposure to 16.
And there was still dynamic room until exposure 20 (limit of photoshop).

So empirically, I would say Terragen store at least 32 - 40 EV's ... but I'm not sure we can compare value that way.

I'm using Terragen sky to lit my scenes all the time 

[reck]

Thanks Paq, that's good to know.

I've never used Terragen to do this before, would you mind briefly explain what the process is and what settings I need to enable? Also how do I make it render 360 degrees?

Thanks

[paq]

Hi Reck :

1) select 'spherical' in the camera option (default is perspective)
2) set camera rotation angle to 0,0,0
3) probably increase the sun disk (light sun option) a little bit to avoid out of range value : 0.6-0.7 should work fine (default 0.5).
4) use an image ratio 2 (something like 1024 * 512)
5) render and save as .exr


Here a example using only Terragen image as only light source in Modo (with importance sampling activated.
The sundisk is responsible of the sharp shadow.

[reck]

Thanks for the little guide Paq. I've just ran through it now and found all the settings you've mentioned so i'll give it a go in Blender and see how it turns out. Looking at your sample image I think it will work quite well.

Do you disable the planet's surface in Terragen so you get purely sky and no horizon line?

I really like Terragen's clouds so i'd like to get them into some of my images as well.

Cheers

[reck]

Very quick test and all worked well 

[Oshyan]

Incidentally the addition of 32 bit EXR output should fix the "out of range" issue with the default sun disk size.

- Oshyan

[paq]

Hi reck,

Yes I othen disable the surface render option of the planet.

Thanks Oshyan, good to know that the 32bits resolve the sun "out of range" problem !