Question on making HDRIs in photoshop using Octane

[xxdanbrowne]

So forgive my noobishness here but I'd like to see if I can make some HDRIs:

It looks like if I take photographs with a real camera of differing exposures I can then merge these into a single scene in photoshop.

So here's my question: I wonder if I could do the same thing using octane to generate the various "photographs".

So if I rendered the same scene a few times with different exposures on the camera and then combined them into a single one in photoshop using Merge to HDRI would it work for e.g. a simple background scene?

Or is there anything else I'd need to look at (such as "stop" - which I'm not clear on).

Thanks

[FrankPooleFloating]

Add a spherical camera > plug this mofo into render target > save out an EXR...

2:1 seems to work good when using for environment map or mapping onto inside of sphere. 4096x2048 is what I use most often.

[xxdanbrowne]

Awesome!

I was wondering on my drive home if EXR was an HDR format but I confess to complete ignorance.
Thanks for the tip: appreciated.

[treddie]

Yes, EXR is "HDR ready". Use Untonemapped, NOT Tonemapped! As FrankPooleFloating has implied, no need to do separate exposures to combine...EXR in Untonemapped mode does that automatically. You can tell when you take the EXR into Photoshop. Do an Exposure adjustment on it and as you drop the exposure, watch the highlights and light sources...They should still be pretty bright compared to everything else going black or very very dark.

Do not worry about it looking wrong colorwise. Just adjust its intensity in Octane when you use it.

[xxdanbrowne]

@Treddie:

Awesome, thanks!

[ROUBAL]

Hi, I tried with my winter landscape scene, to replace the mountains in background and the physical sky by an HDRi. I have put the gamma of the HDRi at 1 and increased the Power of the Environment to 5. It works fine, and the Sun of the HDRi sky casts strong shadows like the original physical one.

[xxdanbrowne]

Hi, I tried with my winter landscape scene, to replace the mountains in background and the physical sky by an HDRi. I have put the gamma of the HDRi at 1 and increased the Power of the Environment to 8. It works fine, and the Sun of the HDRi sky casts strong shadows like the original physical one.

Cool. I read on one of the threads on this forum that HDRI lighting makes the rendering time speed up by a large factor. Did you notice any significant speedup?

[ROUBAL]

I have just updated the images, because I had uploaded wrong images without background !

I have done just a quick test, that's the reason why the brightness is a bit different on the two images. I have rendered few samples and not watched to the rendering time.

EDIT : Tested the speed : In this scene 3.39 Ms/sec with HDRi versus 3.15 Ms/sec with real geometry and physical sky/sun.

The obvious gain that I have noticed on this scene is about memory amount : I saved 1GB of geometry by rendering a panoramic view of the background mountains and using it a 4096x2048 HDRi environment !

My only little problem is that I have some difficulties to match perfectly the location/scale of the mountains between HDRi and the actual mountains to reproduce the scene at identical. Also, the diameter of the environment sphere has some importance if you move the camera at high altitude.

EDIT : I have updated the images in the previous post. Now the HDRi is first and its power is 5.

[treddie]

I think Physical Sky/Sun is always very fast. The problem is when you set up custom emitters. That is where I take a huge hit in render times.

In your HDRI background test, it is a tad blurry, but, unfortunately, Octane does not allow you to go over something like 8000 x 6000 pixels. Not sure why they put a limit on that. So if you increase your resolution to roughly double what you have, it should be a lot crisper, but still not super crisp. But then your texture memory usage goes way up.