High Dynamic Range Imaging (HDRI)

User Guide > Rendering and Render Setup > Lighting > mental ray for Maya Lighting > Final gather and HDRI >

You can use Final Gather to produce image-based lighting (or reflection) with a High Dynamic Range Image (HDRI). Image-based lighting takes the light (and light color) represented in an image you provide to illuminate the scene. An HDRI image has an extra floating point value associated with each pixel that is used to define the persistence of light at that point.

A high-dynamic range image is like several images with different exposures combined to show the full range of light (highlight and shadow). In fact, some HDR images are created by compositing several standard images of varying (bracketed) exposure in a special HDR application. This is required to simulate the wide range of available light in a single image -- an HDR image.

TipTo understand the concept of High Dynamic Range (HDR) images, first think of a cathedral in which bright light spills in through an open door and illuminates part of the interior, except for some of the darker corners. If you were to enter the structure, your eyes would adjust to compensate for the excess or lack of light so that you can see properly.

HDR images have a greater capacity to describe light accurately (by way of floating point numbers) because they store the amount of light (rather than just color) represented in a pixel. This prevents 'blown out' or extremely dark areas in an image that your eyes compensate for in the natural world.

Using HDR images with Final Gather lets you provide extremely realistic lighting.