9

Saving OpenEXR Files 625
Attributes are data that is store d per frame,
not per pixel, and they are embedded in the
file’s header. Channels are data that is store d
per pixel. In order to maximize flexibility with
other s oftware, this plug-in lets you edit the fi le
tags. You should only do this if you know the
tag required by some other software; other wise
it is best to leave the file tags at their default
values.
• Channels that create multiple “slices” in the
EXR file require multiple fi le tags. In this case,
thefiletagintheuserinterfacecomprises
several sub-tags denoted by square brackets.
For example, the Normal channel generates
threeslicesintheEXRfile:onefortheNormal
vector x data, 1 for y, and 1 for z. In this
instance, the tag string in the user interface
would read [NX][NY][NZ], and generate slices
with the file tags "NX", "NY", and "NZ". The
filetagisusedbysoftwarethatisreadingthe
EXR file to identif y the intended use of t he
channel data. Even standard image channels
are encoded this way, with the tags "R", "G",
"B", and "A" used to denote red, green, blue,
and alpha channels respectively.
Extended Attributes
Co mment —A general-purpose comment string
defined by the user. To define the comment,
high light the Comment entr y in the list and then
edit the Comments field immediately below the
list.
Co mputer Name—Thenameofthecomputerthe
image was saved from. In the case of standard
render output during a net render , this is the
machine that rendered the frame.
System Time—The UTC (GMT) system time and
datewhenthefilewaswritten.
Local T i me—The local time and date (corrected for
thetimezone)whenthefilewaswritten.
Version OpenExr —The plug-in version, OpenEXR
API version, and ZLib version in plain text form.
Version 3dsMax—The release version of 3ds Max
itself, the API number, and the SDK revision used
whenthebuildof3dsMaxwascompiled. This
also reports whether the file was generated using
3ds Max or Autodesk VIZ.
Extended Chan nels
Z-B u f f e r—The standard buffer depth channel.
(16-bit or 32-bit floating point)
Object ID—The object ID from the Object
Properties dialog (page 1–117) . (32-bit unsigned
integer)
Material ID—The material effects channel number
(page 2–1443). (32-bit unsigned integer)
Node R ender I D—A u nique object ID set by the
renderer. All objects in the scene have a un ique
Render ID, though the value stored var ies from
renderer to renderer. (32-bit unsigned integer)
UV Coords—The UV coordinates for the object.
Only one UV channel is stored. (two slices, 16-bit
or 32-bit floating point)
Velocity—The 2D velocity vector for the pixel in
screen space. (two slices, 16-bit or 32-bit floating
point)
Nor mal—The surface normal. (three slices, 16-bit
or 32-bit floating point)
Coverage—The pixel coverage of the foremost
object in the pixel. (32-bit unsig ned integer, 16-bit
floating point, or 32-bit floating point)