HDRI Different Types

hi i wanna ask about HDRI
im still learning i have no knowledge or experience in other render engine so my apologies

Q> i saw some HDRI that has full Image Where Image Has Ground and Sky
and some HDRI On Half Line Of Horizon line Top Is Sky and Below Ground line is black or Curve black
last type of image is Spherical Form of HDRI

Q1> what is the difference? why do they differ and have many types of hdri ? is there a pros and cons using them in type of scene? so the lightning will be effective?

Q2> which is the most convenient or use , easy to setup and versatile or all around?

Q3> i notice there is 2 Format for lightning a scene HDRI and EXR what is the difference or pros and cons?
thank you for answers

Q1 / Q2
Equirectangular and “mirror ball” bascially represent two ways of creating a HDR environment map. Mirror ball is easier to create, as you “just” have to take a photograph of a… well… mirror ball, while creating a full 360 degree equirectangular map would require taking a significant number of photographs and stitching them together afterwards. So the latter eventually is more expensive (equipment) and time consuming if you want to do it right.

As far as using them in your scene is concerned, a mirror ball map will be good enough for CG lighting and reflections in most cases. Only drawback is that it’s usually too low-res (and perhaps too distorted) for backdrops. So, you could say that a very high-res equirectangular map is most versatile, as it can be used for lighting, reflections and as a background image. The file size will be gargantuan, though.

As for the “black below the horizon line” thing: In many scenes you won’t see anything of the environment map below the horizon anyway, as you have a 3D ground plane in your scene. So, why not turn the ground area of the environment black in order to save on memory usage?

There is no difference in ease of use between the different types of maps. Only thing you have to remember is to select the correct projection type (Equirectangular / Mirror Ball) in the Environment Texture node:


Q3
Theoretically OpenEXR should be the superior file format in terms of color fidelity AFAIK. But then again, this doesn’t really matter for HDR images you want to use as environment maps. In that regard those are just different file formats to represent (more or less) exactly the same data.

Here is a source for some pretty good HDRI’s:
http://www.hdrlabs.com/sibl/archive.html
There is one problem with HDRI’s in general, especially outside ones (with a visible sun), which is that they don’t have enough exposures to cover the brightness of the sun. I made myself a node setup in order to cope with this, which you can find here:
http://www.pasteall.org/blend/37073
It basically allow you to have 1:1 brightness ratio until a given point, then increase the rate which brightness increases, and set a clipping point. It has a preview feature allowing you to adjust the sliders more intuitively. First/outer black is unaffected. White is where rate is being increased. Second/inner black is where clipping will take place. First adjust to values that makes sense for sun isolation, then turn off preview and adjust until you get a visible terminator caused by the sun (scroll down here to see example of a grey ball measurement in real life, although the ball is a bit more glossy than desired).

thank you very much for quick answer and help. another question

usually my node setup is this which is very common and basic


Q> is there a more advance node setup used so i have more control/ tweak finding the desired exposure

hi and thank you for sharing