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OpenEXR Graphics File Format Turns Up The Contrast - page 2

What is OpenEXR?

  • March 4, 2003
  • By Rob Reilly

"If an image is converted from film (contrast range as high as 10,000:1), to a file format like JPEG, the contrast might drop down to about 1,000:1. This generally matches the contrast range of a typical monitor. And it may look good on your monitor, but differences could soon appear when the image is put back on film, especially after heavy image processing," Kainz explained.

For example, after darkening an image, shiny highlights would turn dullish grey, instead of being bright and sharp.

"The contrast with OpenEXR, known as "half" format, can be as high as 1,000,000,000:1," Kainz said. As a result, computer generated visual effects, such as motion-blur and fog filters, appear natural. Adding artificial motion blur is a fairly common technique used in the motion picture industry.

Additionally, the compression is completely lossless. That means that when the file goes through a compression and uncompression cycle, there is no loss of image quality or detail. Compression ratios are on the order of between 2:1 and 3:1.

The OpenEXR programs were written using ISO standard C++. By using standard C++ and as few operating system specific library functions or language extensions as possible, ILM hopes to make the format and code library easy to port to new platforms.

The format and software were developed on Linux and ported to the Silicon Graphics IRIX platform. Since release, a couple of weeks ago, work has begun on porting the format over to MAC OS10 and Windows. These ports are being carried on in the Open Source community and at other companies. Utilities will eventually be written to convert from other formats to the OpenEXR file format.

Current graphics applications that use the OpenEXR format are 3D Studio Max, Piranha and eyeon Software's Digital Fusion. ILM will soon release OpenEXR drivers for Renderman and probably also for Photoshop.

ILM has also released a program called EXRDisplay, to show the display capabilities of the OpenEXR format. It's really intended as a demo program.

Now, ILM uses the file format on all frames that are passed through or manipulated through the computer.

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