Understanding 'sun' position in a HDRI image

Ruri

Hi all,

Just to clarify, I'm not using the sun-sky. Just pure environment light. The sun I'm referring to is merely the bright dot on the image.

From what I observed in my testing, it seems that although a HDRI image with Dome on, the light is not 360 degree 'active'

The only active light is only the part that can be observed from your camera viewpoint. Is that correct?

Pic 01 with the sun: Assuming I'm a person standing in front of a lake with the sun in front of me, so I get the reflection on the water. Everything seems normal here.

Pic 02 without sun: This is the dome rotated 180degree(same as just orbiting the camera around), no reflection. Even if I walked around the lake, I would still see the reflection right and the light on my shoulder.

 

Thanks all.

 

Hiro Protagonist

The whole of an environment dome is always "active" and this doesn't depend on your field of view (if you put in a mirrored sphere you will see the whole illuminated sphere reflected). I agree you would expect to still see the sun reflecting in a similar way across the water when rotated 180 degrees, as your water plane is presumably in the centre. I'm not at all sure why it isn't so I can't answer that question. What do you see if you position the camera at the opposite side of the plane?

 

Richard Haseltine

That map looks to be pretty dark away from the sun and I suspect is not contributing a lot of light - what happens if you stick a non-reflective object in there?

nonesuch00

It looks OK to me. It's sort of the same effect as looking directly at a light bulb and then turning to face the opposite way from the light bulb. The rest of the room looks dark but it's actually lit as good as it was before you looked at the bulb.

Hiro Protagonist

Richard Haseltine said:

That map looks to be pretty dark away from the sun and I suspect is not contributing a lot of light - what happens if you stick a non-reflective object in there?

I agree. I was wondering whether this is actually an HDRI image but a jpeg image instead. However, I do actually like that foggy background in the second sample—erm, what happened to the images in the OP? I can't see any attachments now, yet the post does not seem to have been edited.

mjc1016

Hiro Protagonist said:

Richard Haseltine said:

That map looks to be pretty dark away from the sun and I suspect is not contributing a lot of light - what happens if you stick a non-reflective object in there?

I agree. I was wondering whether this is actually an HDRI image but a jpeg image instead. However, I do actually like that foggy background in the second sample—erm, what happened to the images in the OP? I can't see any attachments now, yet the post does not seem to have been edited.

I'm still seeing them, so they are still there...

Try logging out and back in.  Sometimes (and I think it's related to page caching) attached images get 'lost'.

Ruri

Hi guys, Answering from phone, sorry. Hiro, Yes, it's from hdri skies.com, one of the morning sets. The tone mapping is default so it's pretty dark. Yes I did try turning the camera around, same effect. Richard, I tested with a bigger cube object, seems to catch the light better than a flat plane with water shader. Anyway I tested a few more hdri sets, those with a stronger sun can get the reflection when turned around... So I suppose it's a matter of hdri. Thanks for feedback. Attachment looks ok from mobile.

Ruri

Have no idea why in the comment box I spaced, but when post it's one clump, sorry about that.

barbult

Ruri said:

Have no idea why in the comment box I spaced, but when post it's one clump, sorry about that.

The same thing happens to me when I post from my phone. It ignores all my paragraph separation.

mjc1016

It seems to be something with the differences in the way the browsers behave.