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622 Chapter 20: Managing Scenes and Projects

first movies to employ OpenEXR were

Harry Potter and the Sorcerer’s Stone,

MeninBlackII,GangsofNewYork,and

Signs. Since then, OpenEXR has become

ILM’s main image file format.

OpenEXR’s features include:

•Higherdynamicrangeandcolor

precision than existing 8- and 10-bit

image file formats.

• Support for 16-bit floating-point,

32-bit floating-point, and 32-bit

integer pixels. The 16-bit

floating-point format, called "half,"

is compatible with the half data type

in NVIDIA’s Cg graphics language

and is supported natively on their

new GeForce FX and Quadro FX 3D

graphics solutions.

• Multiple lossless image compression

algorithms. Some of the included

codecs can achieve 2:1 lossles s

compression ratios on images with

film grain.

• Extensibility. New compression

codecs and image ty pes can easily

be added by extending the C++

classes i ncluded in the OpenEXR

software distribution. New image

attributes (str i ngs, vectors, integers,

etc.) can be added to OpenEXR image

headers without affecting backward

compatibility with existing OpenEXR

applications.

TheOpenEXRBitmapI/Osoftwaregoesbeyond

the “standard” OpenEXR format, taking advantage

of the flexibility of the format itself. It can write

channelsandattributesaswellasgeneralRGBA

data in formats that many OpenEXR file importers

cannot understand, due to implementation limits

as well as lim its to the current set of standards.

The full-latitude 32-bit floating point RGBA files

that the output function can write is one example.

While the OpenEXR API itself fully supports this

capability, and these files are written using the

standard set of OpenEXR libraries, most software

only reads the 16-bit “half” floating point RGBA

files that are considered standard EXR files.

Configuration File Usage

Most bitmap I/O plug-ins, including those

integrated into 3ds Max, store their configuration

information in a binary CFG file that cannot

be edited. To allow external scr ipting support

as well as ordinary preferences, the OpenEXR

software uses a standard INI file format to store its

configuration data. The file is named openexr.ini

and is found in the plugcfg folder in the program

directory. The file is generated automatically the

first time you edit the OpenEXR configuration

settings, and is updated each time you modify an

EXR loader. It is a standard text file and can be

modified with any text editor.

When the INI file is written, it automatica lly

generates a companion “help” text file named

openexr_ini_help.txt.Thisfilecontainsthevalid

ranges for various INI settings, as well as the

various text strings used to specify compression

type a nd bit depth. This file is just a guide; editing

it has no effect, and it is overwritten whenever the

INI file is updated.

To restore the default sett ings af ter editing the INI

file, s imply delete the openexr.ini file and a new

one with t he orig inal defaults will be generated the

next time you edit the configuration settings.