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Saving OpenEXR Files 673
• Zip (per scanline)—Zip-style compression
applied to individual scanlines.
•
Zip (16 scanline block s)—Z ip-style compression
applied to blocks of 16 scanlines at time.
This tends to be the most effec tive sty le of
compression to use with rendered images that
do not have film grain applied.
•
PI Z ( wavelet compression )—Uses a combined
wavelet/Huffman compression. This form of
compression is best for grainy images.
Standard Channels grou p
The standard channels in an image are: red, green,
blue, and alpha (transparency). This group lets
you choose the general type of OpenEXR file to
save, as well as which of the four channels to save
w ith the file. The most widely supported format
is Half Float - 64 bpp format. This stores each
channeloftheimageinaseparatesliceinthefile
using half-type 16-bit floating-point data. The
OpenEXR distribution has features that allow easy
implementation of reading and writing this type of
file, and it is considered a standard OpenEXR file.
Form at —Choose one of the fol lowing from the
drop-down list:
•
Integer - 32 bpp—This non-standard OpenEXR
format contains only a single 32–bit integer
channel. It uses a p ackedIntRGBA image type
in order to support old-style bit depths, such as
32–bit Targa files. Only this pl ug-in can read
this format.
•
Half Floa t - 64 bpp—This 16-bit-per-channel
“half-float” format is standard OpenEXR. Any
software that supports OpenE XR can use this
format.
•
Float - 128 bpp—The 32-bit-per-channel
“ful l-float” format is encoded using standard
OpenEXR channel t ags. Most OpenEXR
implementations will have no problems reading
this format.
R/G/B/Alpha—Let you specify the channels to save:
red, green, blue, and alpha.
Use RealPixel R GB Data—When on, compresses the
essential data of floating-point color into 32 bits.
For technical information, see S
tructure RealPixel.
Note: Image motion blur is not applied to the
RealPixel RGBA data by the renderer. If you are
using Image motion blur, you will not be able to
save RealPixel unclamped color data.
Ex ponent—Enables and sets the power funct ion
exponent to use. This is effectively a gamma curve,
but the exponent is presented in an inverse manner
from typical gamma. The default value is what
exrdisplay expects for input.
Pre-Multiply Alpha—When on, the software uses
premultiplied alpha (page 3–1091) when saving
the file. Pre-multiplying saves computation time if
you later use this image in compositing.
Plugin About—Opens a dialog that shows
information about the OpenEXR plug-in.
Ex tra Channels a nd Attr ibutes—Opens a sub-dialog
(page 3–673)
that lets you specify additional
information to save with the OpenEX R image file.
OK —Accepts any changes and closes the dialog.
Can cel—Discards any changes and closes the
dialog.
Extra Channels and Attributes
To specify an extra attribute or channel to be
included in the saved OpenEXR file, click t he
corresponding + button and then choose the
attribute or channel from the list. To delete an
attr ibute or channel, highlight it in the list and
then click the corresponding X button.