Frequently Asked Questions
What is an HDRI anyway?
Generally speaking, an HDRI (High Dynamic Range Image) is simply an image that contains more than 8 bits of data per pixel per channel. Image formats like JPG and PNG are typically 8-bit and are sometimes referred to as 'LDR' (Low Dynamic Range) images, whereas image formats like EXR and HDR store more data and are therefore HDRIs.
However in the CG world (and on this site) we have come to use the term 'HDRI' to describe a 32-bit 360°x180° equirectangular image that is used for lighting CG scenes.
HDRIs are often used as the only light source in order to create a very realistically lit scene, or to match the lighting from video footage (using an HDRI shot on the same set as the video was taken). But of course they are also used to compliment standard lighting techniques and to add detail to reflections.
How do I use these?
It's super easy, and no different from using any other HDRI. If you're using Blender, here's a 15 second video to show you how it's done.
How many stops/EVs do you capture for each HDRI?
As many as necessary. Usually 12, but sometimes as many as 24 in the case of super-bright light sources like the sun. Regardless of how many EVs were shot, every single HDRI on this site contains the complete dynamic range available in real life, so you won't see any highlight clipping.
Is it 'HDR' or 'HDRI'?
It really doesn't matter which, people generally understand you either way. But if you want something to boast to your English teacher about, 'HDR' stands for 'High Dynamic Range', and the 'I' at the end stands for 'Image'...
So you cannot say 'This is an HDR' because 'high dynamic range' is one big adjective without a noun. But you can say 'This is an HDRI' because 'image' is the noun that is being described as 'high dynamic range'. You can also say 'This is an HDR image', or 'This is an HDR panorama', as long as there's a noun after it.
But like I said, it doesn't really matter. 'HDR' and 'HDRI' are both commonly used as nouns that mean the same thing.
How do you measure the dynamic range (EVs)?
The number of EVs (or 'stops') is based purely on the number of brackets captured. For example, 12 EVs means 5 photos were taken with 3 EVs between them (shutter speeds: 1/4000, 1/500, 1/60 1/8, 1"), and since there are 4 gaps of 3 EVs between them, the dynamic range is said to be 12 EVs (4x3=12).
Unfortunately there is no standardized way for measuring the dynamic range of an HDRI. Different people use different methods, so there's no reliable way that you as a user can tell whether website-A that claims 50 EVs of dynamic range is actually better than website-B that has 20 EVs.
The main thing to look out for is whether an HDRI is unclipped or not. They usually don't mention anything if it is indeed clipped, so watch out. Being unclipped means the full range of brightness in the scene was captured, including the super crazy bright sunshine. If an HDRI is clipped (aka "clamped"), it will produce unrealistic lighting which is usually flat and lacking contrast.
What equipment/software do you use?
This changes fairly often, so take a look at my long ass article on creating your own HDRIs to answer your actual question ;)
There you'll find several sections explaining the various advantages and disadvantages of different types of equipment and software - there are many ways to skin a cat, though some are more effective than others.