Output Shaders
Output shaders are user-written functions that can be linked at
runtime that have access to every pixel in all available frame
buffers after rendering. They can be used to perform operations
like post-filtering or compositing.
Files to write are specified with data type, file format and
file name. If the data type is omitted a default data type is used
that is assumed to be the "best" type for the given image format.
This default type is marked "
" in the
table below. The data type implies the frame buffer type. There are
special file formats for depth, vector, and label files, in
addition to a variety of standard color file formats. By listing
the appropriate number and type of output statements, it is possible to
write multiple files. For example, both a filtered file and the
unfiltered version can be written to separate files by listing
three output statements: one to
write the unfiltered image, one that runs an output shader that
does the filtering, and finally another one to write the filtered
image. Output statements are executed in sequence.
The following file formats are
supported:
| format |
type |
compress |
description |
| pic |
rgba |
RLE |
Softimage color |
| Zpic |
z |
- |
Softimage depth map (write only) |
| alias |
rgb |
RLE |
Alias color |
| rgb |
rgba |
RLE |
Silicon Graphics 8-bit
RGBA color |
|
rgb |
RLE |
Silicon Graphics 8-bit RGB
color |
|
rgba_16 |
RLE |
Silicon Graphics 16-bit
RGBA color |
|
rgb_16 |
RLE |
Silicon Graphics 16-bit
RGB color |
| jpg |
rgb |
JPEG |
JFIF picture |
| png |
rgb |
RLE |
Portable Network Graphics 8-bit RGB color |
|
rgba |
RLE |
Portable Network Graphics 8-bit RGBA color |
| exr |
a |
 |
OpenEXR 8-bit scalar |
|
rgb |
 |
OpenEXR 8-bit RGB color |
|
rgba |
 |
OpenEXR 8-bit RGBA color |
|
a_h |
 |
OpenEXR 16-bit scalar |
|
rgb_h |
 |
OpenEXR 16-bit RGB color |
|
rgba_h |
 |
OpenEXR 16-bit RGBA
color |
|
a_fp |
 |
OpenEXR 32-bit scalar |
|
rgb_fp |
 |
OpenEXR 32-bit RGB color |
|
rgba_fp |
 |
OpenEXR 32-bit RGBA
color |
|
z |
 |
OpenEXR depth map |
|
n |
 |
OpenEXR normal-vector
map |
|
m |
 |
OpenEXR motion-vector
map |
| tif |
rgba |
RLE |
8-bit RGBA TIFF |
|
rgba_16 |
RLE |
16-bit RGBA TIFF |
|
rgba_fp |
RLE |
floating-point RGBA TIFF |
|
rgb |
RLE |
8-bit RGB TIFF |
|
rgb_16 |
RLE |
16-bit RGB TIFF |
|
rgb_fp |
RLE |
floating-point RGB TIFF |
| tifu |
rgba |
- |
8-bit RGBA TIFF |
|
rgba_16 |
- |
16-bit RGBA TIFF |
|
rgba_fp |
- |
floating-point RGBA TIFF |
|
rgb |
- |
8-bit RGB TIFF |
|
rgb_16 |
- |
16-bit RGB TIFF |
|
rgb_fp |
- |
floating-point RGB TIFF |
| iff |
rgb |
RLE |
Alias Maya 8-bit RGB image |
|
rgba |
RLE |
Alias Maya 8-bit RGBA image |
|
rgb_16 |
RLE |
Alias Maya 16-bit RGB image |
|
rgba_16 |
RLE |
Alias Maya 16-bit RGBA image |
|
rgba_fp |
RLE |
Alias Maya float RGBA image |
|
a |
RLE |
Alias Maya 8-bit alpha |
|
a_16 |
RLE |
Alias Maya 16-bit alpha |
|
a_fp |
RLE |
Alias Maya floating-point alpha |
|
z |
RLE |
Alias Maya depth map |
| rla |
rgba |
RLE |
8-bit or 16-bit Utah/Wavefront color, type A |
| rlb |
rgba |
RLE |
Utah/Wavefront color, type B |
| picture |
rgb |
RLE |
Dassault Systèmes CATIA PICTURE |
| hdr |
rgbe |
- |
Radiance high dynamic range
color, 8-bit RGB color |
| ppm |
rgb |
- |
Portable pixmap, 8-bit P6 binary |
| tga |
rgba |
- |
Targa color |
| bmp |
rgb |
RLE |
MS Windows and OS/2 color |
| qntpal |
rgb |
YUV |
Abekas/Quantel, PAL (720 576) |
| qntntsc |
rgb |
YUV |
Abekas/Quantel, NTSC (720 486) |
| ct |
rgba |
- |
mental images 8-bit color (3) |
|
rgba_16 |
- |
mental images 16-bit color (6) |
|
rgba_fp |
- |
mental images floating-point color (11) |
| st |
a |
- |
mental images 8-bit alpha (4) |
|
a_16 |
- |
mental images 16-bit alpha (7) |
|
a_fp |
- |
mental images floating-point alpha (15) |
| vt |
vta |
- |
mental images alpha basis vectors (5) |
| wt |
vts |
- |
mental images intensity basis vectors (5) |
| zt |
z |
- |
mental images depth map (8) |
| nt |
n |
- |
mental images normal-vector map (9) |
| mt |
m |
- |
mental images motion-vector map (12) |
| tt |
tag |
- |
mental images normal-vector map (10) |
| bit |
bit |
- |
mental images mask bitmap (13) |
| cth |
rgbe |
- |
mental images HDR color, 8-bit RGB color (14) |
| map |
any |
- |
mental images memory map |
| null |
- |
- |
null, deleted on close, write only |
OpenEXR [6] in
mental ray 3.4 supports the compression modes RLE (default), PIZ
(wavelet-based), ZIP, and PXR24 [7]. The
first three are lossless; PXR24 is lossy if the written data is
stored in full floating-point precision and lossless otherwise.
mental ray 3.3 and earlier always uses ZIP compression.
Each of these file formats implies a particular default data
type (the first entry in column "Supported data types"); for
example, "jpg" implies 8-bit RGB, and "zt"
implies Z. The default data type may be overridden by explicitly
specifying another data type, such as a 16-bit type, in the
output statement, as long as it
is supported and appears in the above table. mental ray will adjust
its frame buffer list to compute the requested types. For example,
the standard RGBA frame buffer stores 8 bits per component by
default, but if any output statement references a 16-bit type, the
RGBA frame buffer also switches to 16 bits.
The null file format is useful to create a stub file
during rendering, that can be used to attach the imf_disp
viewer, without leaving the file on disk when rendering
finishes.
The rgb_h and rgba_h image types are supported
only for OpenEXR output
statements. They cause the data to be written to the OpenEXR file
in half-float format. mental ray's frame buffer is stored in full
floating point format. This allows the full dynamic range without
the storage overhead of storing full floating-point values in the
OpenEXR file. mental ray 3.3 does not support half-float frame
buffers.
The RGBE high dynamic range color data type can
store RGB data whose components may exceed the value of 1.0, which
is the normal limit for standard RGB data. There are two
specialized file formats (HDR and CTH) for RGBE, but mental ray
will also allow storing RGBE data in any 8-bit RGBA format, such as
SGI RGB. This will result in images that cannot be displayed by
standard viewing programs because they would interpret the data as
RGBA, but it has become common practice to use such formats to
transport RGBE data to other tools that understand RGBE.
The available data types are:
| type |
comp |
bpc |
contents |
| rgba |
4 |
8 |
RGBA color |
| rgba_16 |
4 |
16 |
RGBA color (16 bits per component) |
| rgba_fp |
4 |
32 |
RGBA color (floating-point) |
| rgb |
3 |
8 |
RGB color |
| rgb_16 |
3 |
16 |
RGB color (16 bits per component) |
| rgb_fp |
3 |
32 |
RGB color (floating-point) |
| rgbe |
4 |
8 |
high dynamic range RGB
color |
| a |
1 |
8 |
Alpha channel |
| a_16 |
1 |
16 |
Alpha channel (16 bits per component) |
| a_fp |
1 |
32 |
Alpha channel (floating-point) |
| s |
1 |
8 |
synonymous with a |
| s_16 |
1 |
16 |
synonymous with a_16 |
| s_fp |
1 |
32 |
synonymous with a_fp |
| z |
1 |
32 |
depth channel |
| n |
3 |
32 |
normal vectors |
| m |
3 |
32 |
motion vectors |
| tag |
1 |
32 |
label channel |
| vta |
2 |
16 |
UV vector texture |
| vts |
2 |
16 |
synonymous with vta |
| bit |
1 |
1 |
bitmask channel |
| coverage |
1 |
32 |
coverage of most important object |
The difference between "vta" and "vts", and
between n and m, is significant only when
automatic conversions are done. The file contents are identical
except for the magic number in the file header.
The floating-point RGBA data type "rgba_fp" allows
color and alpha values outside the normal range 
, and no dithering is applied even if explicitly
enabled. In contrast, any conversion to the 8-bit or 16-bit formats
will clamp values outside this interval. Note that dithering
reduces the effectivity of RLE compression.
All mental images file
formats contain a header followed by simple uncompressed image
data, pixel by pixel beginning in the lower left corner. Each pixel
consists of one to four 8-bit, 16-bit, or 32-bit component values,
in RGBA, XYZ, or UV order. The header consists of a magic number
byte identifying the format, a null byte, width and height as
unsigned shorts, and two unused null bytes reserved for future use.
All shorts, integers, and floats are big-endian (most significant
byte first).
mental ray can combine
samples within a pixel in different ways. The combination of
existing samples can also pad
the frame buffers to "bridge" unsampled pixels.
Interpolation of colors, depths,
normals, and motion vectors means that they are averaged, while
interpolation of the labels means that the maximum label is used
(taking the average label is not a good idea). Interpolation of
depths only takes the average of non-infinite depths, and
interpolation of normals and motion vectors only takes the average
of vectors different from the null vector. Interpolation is turned
on by writing a "+" in the beginning of the output type and turned
off by writing a "-" there. For example, to interpolate the depth
samples, write "+z" in the output statement:
| type |
meaning |
| -rgba |
last color |
| +rgba |
average color |
| -z |
lowest depth |
| +z |
average depth, excluding infinite depths |
| -n |
last normal |
| +n |
average normal, excluding null vectors |
| -m |
last motion vector |
| +m |
average motion vector, excluding null vectors |
| -tag |
last label |
| +tag |
maximum label |
If interpolation is turned off for a frame buffer, the last
sample value (color, normal, motion vector, or label) within each
pixel is stored, and pixels without samples get a copy from one of
the neighbor pixels. Interpolation off for depth images is an
exception: rather than using the last sample depth, the min depth
is used - this can be useful for compositing. Interpolation is on
by default for color frame buffers (including alpha and intensity
frame buffers) and off by default for depth, normal, motion vector,
and label frame
buffers.
The distribution of
OpenEXR requires the following copyright notice:
Copyright (c) 2002, Industrial Light & Magic, a division of
Lucas Digital Ltd. LLC
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
- Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
- Redistributions in binary form must reproduce the above
copyright notice, this list of conditions and the following
disclaimer in the documentation and/or other materials provided
with the distribution.
- Neither the name of Industrial Light & Magic nor the names
of its contributors may be used to endorse or promote products
derived from this software without specific prior written
permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
OF THE POSSIBILITY OF SUCH DAMAGE.
The distribution of the
PXR24 compressor requires the following copyright notice:
Copyright (c) 2004, Pixar Animation Studios
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
- Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
- Redistributions in binary form must reproduce the above
copyright notice, this list of conditions and the following
disclaimer in the documentation and/or other materials provided
with the distribution.
- Neither the name of Pixar Animation Studios nor the names of
its contributors may be used to endorse or promote products derived
from this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
OF THE POSSIBILITY OF SUCH DAMAGE.
Copyright © 1986-2007 by mental images GmbH