Stupid dome question of the day

[Benny]

This is probably so obvious that I won't get an answer but here we go.

I typically use the hdr environment directly on my exterior shots, as I've never been very happy with the fringing I get from the alpha when replacing the sky in post. I've bought some quality hdrs that I typically use so this is normally pretty straight forward. However, I now want to use some hdr where the exposure is either to weak or strong (or uninteresting) and I'm playing with a big inverted dome and a sky texture map with self illumination but not getting the results I was expecting.

How does an environ map really work? Is it infinitely outside this sky object dome or can I make my dome big enough to have the environment on the inside? How can I use an hdr map (loaded via VRAYHDRI if that matters) with my sky dome (that doesn't really add any light affects the scene) and be certain it won't affect/obscure the lighting of the scene? I've played with the object properties but I remember that had another set of properties in Vray. I want the reflections of the dome in my window but nothing else.

Thank you in advance for your patience with me here.

[PROH]

Hi. I don't use Vray, but I can help you with some of your questions.

- The environment map will always be outside any object in the scene. So you can't make the dome bigger and have the environment inside.

- I know this (oldschool?) technic with using a dome, but if it doesn't fulfill a very specific function that can't be reached any other way, then I wouldn't use it. If you only want to use it as a reflection map, then put the sky texture in the reflection override slot instead.

Hope it helps

[Benny]

Thanks for your reply.

Yeah, I was kind of understanding that I guess, it makes sense the environment is infinite large. The reason I want to try to understand how to use a dome is that I want to control and see my sky directly in the render without the fringing issue in Photoshop, and the same goes for reflections, seeing the map in the viewport makes it easier to place reflections in windows etc.

Keen to know how others do.

[PROH]

Then set the the renderer to use "Corona" instead of "Max Environment". Put your light source HDRI into the Corona slot, and put your sky map into the reflection override slot AND Max's environment slot. Now it's possible to see the sky map in the viewport without using it as light source.

Hope it helps

[mraw]

I think it would be worthy to look at your 'fringing' problem in Photoshop. Is it possible that this fringing you experience derives from a premultiply error?

[Juraj]

I think it would be worthy to look at your 'fringing' problem in Photoshop. Is it possible that this fringing you experience derives from a premultiply error?

Even if people use remove matte or similar technique, they usually try to add darker tonemapped skies than the ones renderer with. You need darker (ideally black) override for that.

I always wondered why it's not possible just to specify the alpha to ignore intensity and simply pretend the environment is black :- ). You could then have the best of both world, sky in the render, and perfect alpha for compositing. Now you have to choose.

[mraw]

Ah, thanks Juraj. Now I understand what's the 'fringing'-problem here (at least I think so). If you're tweaking the colors in post this 'fringing' will appear, because the original colors of the background are multiplied in the edge. Always render on black(alpha), when you want to do post-work.

[Benny]

Then set the the renderer to use "Corona" instead of "Max Environment". Put your light source HDRI into the Corona slot, and put your sky map into the reflection override slot AND Max's environment slot. Now it's possible to see the sky map in the viewport without using it as light source.

Brilliant, thanks for your help guys.