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616 Chapter 20: Managing Scenes and Projects
• C ompositing: Using 16–bit images in a
compositing pipeline can quickly become
a problem as colors are manipulated. For
example, banding may appear.
• HDR images are not bound to a specific
range (e.g., 0-255 or 0-65535); they have a
dynamic r ange. As such, hig h-contrast and
physically accurate values can b e stored in
32-bit floating-point pixels.
• Because of their large range of values, HDR
images can easily be modified, and effects can
be reapplied long after rendering, without
affecting the quality of the image. For example,
changing the contr ast/brightness/exposure of a
16-bit image could ca use banding, which would
require re-rendering the image. Ho wever, the
sameoperationonanHDRimageshouldnot
affect its qual ity.
Clicking Save or Setup in the Render Output File
dialog (page 3–9) displays the HDR Save Sett ings
dialog.
The dialog lets you choose the source of the values
used for output:
• Higher dy namic range and color precision than
existing 8- and 10-bit image file formats.
• Support for 16-bit floating-point pixels. The
pixel format, called "half," is compatible with
thehalfdatatypeinNVIDIA’sCggraphics
language and is supported natively on their
newGeForceFXandQuadroFX3Dgraphics
solutions.
• Multiple lossless image compression
algorithms. Some of the included co decs can
achieve 2:1 lossless compression ratios on
images with film grain.
• Extensibility. New compression codecs and
image typ es can easily be added by extending
the C++ classes included in the OpenEXR
software distribution. New image attributes
(strings, vectors, integers, etc.) can be
added to OpenEXR image headers without
affecting backward compatibilit y with existing
OpenEXR applicat ions.
IFL File Format
AnIFL(ImageFileList)fileisanASCIIfilethat
constructs an animation by listing single-frame
bitmap fi les to be used for each rendered frame.
When you assign an IFL fi le as a bitmap, rendering
steps through each specified f rame, resulting in
an animated map.
(In a similar way, if you assign an AVI file or MOV
file as a bitmap, rendering steps through each
frame of the animation.)
For example, if you assign a 10-frame animation of
a blinking red "Danger" sig n to a material’s diffuse
component, apply the material to a cube, and then
render a 30-frame animation, the cube displays the
blinking red Danger animation three times.
The .ifl file lists t he bitmap files to be used with
each frame. You can append an optional numeric
argument to each file name to specify the number
of frames of rendered animation on which it is
used. For example: