High Dynamic Range Images

HDRI stands for High Dynamic Range Image . What we've been used to up until now are LDRI, or Low Dynamic Range Images. These traditional image formats represent a limited range of intensity values for each pixel (most commonly 0 to 255 for each of the red, green and blue channels), sufficient for on-screen images. High Dynamic Range Image formats allow a much greater range of intensity values, by using floating-point values for each pixel. This feature allows these images to be used to represent light intensities present in the real world. The technique, known as image-based lighting (IBL), is designed specifically to produce incredibly realistic lighting effects in rendered images, and to essentially replace the more traditional lighting setup.

On a day-to-day basis, HDRIs are the perfect new technology for two reasons. Firstly, the simplicity inherent in using a single image to light an entire scene allows the creation of more accurate images faster. Not only do HDRIs provide vastly enhanced levels of realism, but also avoid the need to painstakingly set up complex lighting arrangements. Secondly, they allow lighting to be perfectly matched to background images and environments. If this were to be done with an external building shot, the surrounding HDRI would be able to provide not only a convincing approximation to natural daylight conditions, but also include the surrounding environment reflections. All of this along with the environment mapping and reflection possibilities, provides a simple-to-use yet incredibly powerful realism tool.

The following examples have been rendered within LightWorks, and show an example of some Tadao Ando architecture, highlighting the differences that HDRI and Image Based Lighting can make to a scene:

Traditional lighting produces a render with which to compare our HDR Images against.

An example of how an HDR Image used to light the scene can create a feeling of warmth and a greater degree of realism, especially apparent in the shadowing.

An alternative example, using a clear sunny day as the Image Based Light. The coloration and shadowing change dramatically, giving a very different character to the scene.

So, HDRI lighting looks great in rendered scenes, but what about product design? We have a couple of products you may be familiar with. Have a look and judge for yourself the quality of this rendering method:

HDRI images can be created through the use of either a light probe, or a digital camera in combination with either a silver ball or a fish-eye lens. Tutorials on how to create an HDRI image can be found by following the links given below.

Images are then combined in a specialist piece of software, of which several are available for use (see Guide to HDRI software), and the output is one of the following four types of HDRI environment map:

Images can be converted between these formats using specialist software found again by following the links given below.

There are also a whole host of file types that these maps are stored in. OpenEXR and HDR are two of the more popular:

• OpenEXR (.exr) is a high dynamic range image format developed and made freely available by Industrial Light and Magic (ILM). It uses 16-bit floating point values for each pixel, (representing the equivalent of well over 30 f-stops in photographic terms), and can be supported natively on the latest graphics cards.
• HDR (.hdr) (Radiance format) is another popular format, providing a similar range to OpenEXR but with slightly less accuracy. There are many sources of HDR images available online, including some commercial image libraries.

Despite the obvious new-technology format wars going on, the choices of map and file type give different advantages and disadvantages depending on what you want to do with them. To suggest the perfect one here would raise a whole host of objections, but it is safe to say that none of those mentioned would be a bad place to start, and it is the technology behind HDRIs, and not simply the HDRIs themselves that produce the leaps in productivity and lighting realism.

It is one of those technologies that has to be seen to be believed. It could forever change the way lighting is used in rendering.

In conjunction with the recent release of High Dynamic Range Image functionality within LightWorks, we have joined forces with three of the best HDRI producers in the world to bring you a stunning collection of HDR image files to use in your designs.

To access this collection, click here.

LightWork Design is working closely with some of the world's leading HDRI suppliers, to give users of LightWorks an unprecedented level of quality and realism in their rendering. The links below give you the opportunity to experience the quality of their HDRIs first-hand.

http://www.sachform.de - Sachform Technology GbR is a german based company specializing in HDRI-related products and services for DCC professionals. HDRI-databases as well as HDRI on demand services are the key technologies in their portfolio. Images are available in all four .hdr formats, which can be used for testing purposes, but which should be purchased prior to commercial use.

http://www.realtexture.com - Realtexture offers a wide range of unique and interesting textures and backgrounds, for both 3D productions and game design, also offering the creation of individual HDRIs on demand, either artificial or real-world. All HDRIs are available for purchase in all four .hdr formats.

http://www.doschdesign.com - DOSCH DESIGN was founded in 1995 and provides a comprehensive product line-up supporting computer graphics specialists and animation artists, as well as a multitude of visualization, presentation & print material projects. All images are "license-free" - no further cost or fees are due when used commercially. A large number of images are available for purchase in all four .hdr formats .

http://www.hdrimaps.com - HDRImaps is two designers/photographers from Chicago, Il USA, wanting to support the growing format of HDRI and to explore it further, using unique real-world environments during photo shoots to achieve unique visual effects within HDRI imagery. A more specialized set of images is available in all four .hdr formats, all of which are available for purchase.

• http://debevec.org/Probes/ - Provides images in .hdr vertical cross form which can be used for testing purposes but which should not be published or distributed in any way without permission from the web site author.
• http://www.luminance.londonmet.ac.uk/webhdr - A personal HDR creation service

Several third party software tools currently exist to allow HDRIs to be created from multiple photographs taken at different light exposure levels, and as interest in, and knowledge of, high dynamic range image formats and their usefulness grows, it is likely that more and more such tools will appear in the market. Here are some of the best currently available:

• HDRShop - A Windows only tool, free for noncommercial use only.
• HDRView - A Comprehensive Windows HDRI Viewing tool.
• Photosphere - A Macintosh image browsing and cataloging tool which can be used freely.
• hdrgen - The HDR composition engine used within Photosphere is also available as a command-line tool for Linux as well as Macintosh.