re Using HDRI to light a scene

Ruz

so there are two things here, providing reflections from the sharper/High res version of the HDRI. From what I understand you are supposed to actually light the scene with a smaller blurry version of the same HDRI. I guess if you are using a sky with a bland sky groundscape then its not so much an issue Most of the older HDRI sets I used to download had the blurry version included like the Zion_Sunsetpeek set OR is it the case these days that you just use the HDRI as ambient light?
its confusing because most people just seem to download a HDRI from PolyHaven or similar and bung it in the background to both provide light ' and' reflections.
I have heard that this is the wrong approach and that a small blurry version is good enough to light the scene, but then you have a high res background plate for the reflections

I actually saw an arch viz guy post that he would never use a HDRI to light his outdoor scene

What is the correct approach?

gnoop

When you say light the scene  you mean "sky"  light  or "environment"  light, right?    Because  HDRI taken from photos usually doesn't  have enough  light intensity in what supposed to be sun  area there.    It could  if you render  background in a 3d soft but usually don't.  So you still have to setup  sun light source and environment light intensity with proper proportion and related position.  

 

   Fewer pixels  "sky" light  image  is   fewer calculations it requires   usually  but some renderers  have samples sliders  so it might be irrelevant and could be set in the render itself.   Reflections could be just a  texture  projection  and for perfectly polished things  you sometimes need higher res   reflections.

Your arch viz guy don't use HDRIs  because  they provide you with  very time specific and context  related  indirect illumination only .   For a big  outdoor scene you would need  new HDRI  for each few meters  of space.     Next to an illuminated building wall is one condition. Few steps away  and it's totally different and unrealistic  already.      So people tend to use so  called "sky models"  almost every render has now.    it's a matter of choice.

Ruz

yeah I do use the sky model in blender on the whole, but its a very saturated look. it passable though for my purposes
So you should n't really be a using a HDRI to light a big scene, even as ambient light?.

i generally use the sun position addon to combine the HDRI with a single sunlight  which matches the sun position form the texture.
again looks pretty ok
Some HDRI's 'do' have enough stops to light the scene though, I have a few with 24 stops and you get harsh sunlight with them, but i was mainly wondering why some people use the high res HDRI to actually light whole scene, not the blurry version as an ambient light.
I guess they want sharp reflections from the HDRI

interesting that the HDRI is only correct from one position, never knew that 

Eric Chadwick

People use the pre-filtered (blurry) HDRI for real-time rendering because it’s faster to use with surfaces using Roughness in your materials.

Conversely, architectural visualization often has to simulate how the sun will shine into windows, at specific longitude, season, and time. Which affects air conditioning, etc.

So, you need a configurable and accurate sun system.

Ruz

yeah I am trying to get a balance between accuracy and a nice illustrative look. I just wanted to know the correct way to do stuff
as quite often i find a a Full HRDI image fights with my scene, covering it in  colors which I don't really need.
A lighting system, although not perfect seems better. Still not sure if I am happy with the Blender lighting system or if its just me doing it wrong
I always just used HDRI as ambient light , thne add a strong sunlight for contrast. works ok , depending on the HDRI, but can be a bit inconsistent

gnoop

Ruz said:

interesting that the HDRI is only correct from one position, never knew that 

If it's just blue sky , sun and ground surface  in the HDRi it's  irrelevant , could be  universal for a whole scene. Just  static time of day . 

If HDRi has a big  green trees taking half of the image it would cast   green  all over your scene.   So too specific for some exact place.    That's why  in movies sometimes  they actually run with a gray and polished  balls on a stick to capture ambient light and reflections   all along a way  CG character  is supposed to move through in a  real life scene.

Well ,they  did it before . Now  the whole scene is CG only probably  so no need to capture anything