“HDRI” stands for High Dynamic Range Image. “Dynamic range” is the measurement of how much brightness information is contained in an image, so a “high dynamic range” image is an image that has a very large range of brightness, more than you can see on your screen in one go actually.
Most photos and images, in general, are what I call “LDR” images or Low Dynamic Range images. They store 8 bits of data for each of the red, green and blue channels for every pixel. An example of an LDR image is a JPG file.
The problem with LDR images is that they are limited to a relatively small range of brightness, from 0 to 255, which is not actually all that much.
If you want to light a 3D scene using an image, what you really need is a format that can store more than just 8 bits of data per channel so that you can have a much larger range of brightness. Luckily, there are several formats that can do this, the most common of which has the extension “.hdr”.
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, 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 complement standard lighting techniques and to add detail to reflections.
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 (4×3=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 customer 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 IS SO SPECIAL ABOUT HDRI?
HDRI is a much higher dynamic range of color and values than traditional bitmap formats. Instead of encoding colors like a computer monitor, using 24-bits of color for each pixel, HDRI is modeled after trichromatic base of the human eye and store actual luminance values in each pixel. So not only is color contained but the strength and brightness of the light at that point in the map. The range of color and light that can be contained in this format is much greater than the RGB scale of traditional computer graphics. nXt uses HDRI values throughout the rendering process, putting nXt into the classification of HDRR (High Dynamic Range Rendering)
In HDRI, each channel holds more accurate values. For instance, if you look at a 60 watt light bulb, it will be white. But if you look at the sun it is also white, but 10,000 times brighter. If you look at a star in the night sky, it is also white, but may be 1,000 times dimmer than the light bulb. In RGB, white is white, in HDRI, light has a much greater range and can capture the actual amount of light coming from each of these sources.
WHY USE AN HDRI?
There is no easier or quicker way to light a CG scene than to use an HDRI. They are essentially snapshots of the real world that contain exquisitely detailed lighting information, which can transport your bland CG objects into realistic virtual environments.
Not only do they provide accurate lighting, but they can be seen in the background and in reflections, which makes them all the more immersive.
HOW TO USE AN HDRI?
need some videos here for each software. Mainly SketchUp, Cinema 4D and 3dsmax.
There are various ways to make an HDRI, but it’d be impossible to cover every detail so I’ll show you a method that gives you decent results with a reasonable amount of effort.
The following HDRi products are the ones I use myself and I feel very confident recommending them to you. Enjoy!
Bertrand Benoit posted on the forums about a wonderful VRay balloon material he is offering for free. Looks incredibly real to me, and ORANGE!
XFrog Inc. has made available for you to download 130 free 3d plant and tree models from each of the 30 XfrogPlants libraries! Three to nine 3d plant models are included in each of the 30 species they provide (with all major formats included), and best of all, they are completely FREE! Download the plants, browse their documentation PDFs and try in your favorite software.