Working With HDR images

What's the problem with jpgs?

Typical photographs can either display extreme highlights or lowlights, but not both at once. In the example images below, note how the exposure allows either the interior room to be exposed, or the exterior parking lot. This makes them poor choices for use in IBL (image based lighting) and as displacement maps.

This post is part 2 of a short series on image based lighting. Part 1 here .


Imitating real-world lighting

In real life, your eyeball can handle both lighting conditions at the same time. In order to create photo-realistic lighting in CG images however, you need wide range of exposures. In other words, a more dynamic range of lighting.

HDR images contain multiple exposures and therefore produce better results than their jpeg counterparts. For example luminance values of jpeg can be recorded as values of 0-255 (black to white) vs an HDR which can have ranges of 0-20,000+ (negative black to super white)!


The photos above were use to create an HDRI for the HDR Path Environment Light asset.


Can my cell phone can do that?

Probaby not.
Not all background images are created equal. To complicate matters, the term HDR has been hijacked by the consumer camera market. Lots of cameras and smartphones can take panoramas. Some will even do so at multiple exposures, combine them, and call this an HDR image....which it isn't. When several exposures are combined like this, and saved as a jpeg, the result is a "tonemap" of an HDR image. Although camera companies are using the term HDR..


High Dynamic Range Image format


Standard jpegs have 8-bits of information per channel. HDRs have 16 or 32 bits. So they take up more disk space and are only supported by a few formats such as Radiance (.hdr), Open Exr (.exr). Tiff-16, and Tiff-32 (.tif).
Very few cameras in the world shoot these natively. Usually one must purchase these images online, or create them in photoshop from multiple exposures.
When these images are used in a CG rendering context, one needs to be aware that the panorama can come in many different layouts. Just like a map of the world is like an unwrapped sphere, so is a panorama. Commercial HDR images (for rendering) can come in many standard layouts. These correspond to how the image will be applied to a virtual sphere or cube at render time.

Here are a few examples of environment map layouts:

Stay tuned for a post on creating your own HDR images!