Deep color. (viewpoint Film).(using OpenEXR format)

In late January, Industrial Light & Magic (San Rafael, California) released source code for its proprietary, extended dynamic range image-file format into the open source community. Dubbed OpenEXR, the format provides a possible standard for 16-bit floating-point color images.

16-bit floating point gives people who manipulate color and contrast in scanned images much more elbowroom than the commonly used 8-bit and 10-bit formats. In addition, if widely adopted, it would help studios exchange high dynamic range image files.

Created for internal use in 2000, tested on such films as The Time Machine (see CGW, March 2002, pg. 24), Men in Black II, and Gangs of New York, and currently utilized for The Hulk and other films, OpenEXR was devised by ILM software engineers Florian Kainz and Rod Bogart.

Although the source code has been available for only a few weeks, support for the standard is growing among computer graphics hardware and software vendors. It's too early to say for sure, but it looks like the effort put forth at ILM to turn its proprietary code into a format suitable for public consumption will pay off.

"The advantage from our side is that you can color correct an image and remove those corrections later without image degradation," says Tom Benoit, founder of Interactive Effects, which is supporting OpenEXR in its Amazon Paint and Piranha visual effects products.

To demonstrate this, developer Kainz points to his computer screen, which shows a scanned photograph of an office that was saved as a JPEG image, an 8-bit file format. "When I make the image half as bright, which is something we might want to do in post processing, the window should still be white, but it's murky gray," he says. What's more, the window is the same shade of gray as a piece of white paper in the photo even though, in reality, the window should be several times brighter.

"The white was limited to being as bright as the screen could display because with the 8-bit formats, you have only 256 values per [RGB, for example] channel," Kainz explains. "But with 16 bits, you get 65,000 values per channel." That means you could have trillions of colors. But why? "The point of having so many values per channel is that within a wide range of brightness levels, any conceivable color can be represented very accurately," Kainz says.