Subband Encoding of High Dynamic Range Imagery
Greg Ward,
Sunnybrook Technologies
Maryann Simmons, Walt Disney Feature Animation
ABSTRACT
The transition from traditional 24-bit RGB to high dynamic range (HDR) images is hindered by excessively large file formats with no backwards compatibility. In this paper, we propose a simple approach to HDR encoding that parallels the evolution of color television from its grayscale beginnings. A tone-mapped version of each HDR original is accompanied by restorative information carried in a subband of a standard 24-bit RGB format. This subband contains a compressed ratio image, which when multiplied by the tone-mapped foreground, recovers the HDR original. The tone-mapped image data may be compressed, permitting the composite to be delivered in a standard JPEG wrapper. To naive software, the image looks like any other, and displays as a tone-mapped version of the original. To HDR-enabled software, the foreground image is merely a tone-mapping suggestion, as the original pixel data are available by decoding the information in the subband. We present specifics of the method and the results of encoding a series of synthetic and natural HDR images, using various published global and local tone-mapping operators to generate the foreground images. Errors are visible in only a very small percentage of the pixels after decoding, and the technique requires only a modest amount of additional space for the subband data, independent of image size.
Supplemental materials for APGV04 paper
Herein we include encoding results from two typical image examples: an HDR capture of DyrhamChurch, and a Radiance rendering of a Hotel. To jump to the associated page, click on an image, below.
Captured image of DyrhamChurch.
(Click to go to comparison page.)
Radiance rendering of Hotel.
(Click to go to comparison page.)
Some of the links on these pages are for HDR images you may
wish to compare in Radiance RGBE
format. Depending on your system,
you may download a viewer for this format from one of the following websites:
Windows HDRshop:
http://www.debevec.org/HDRShop/
Mac OS X Photosphere:
http://www.anyhere.com
Unix Radiance:
http://radsite.lbl.gov/radiance/download.html