9

GIF Files 613
Units—Select inches or millimeters.
Image Or ientation—Select portrait (tall) or
landscape (wide).
Dat a For mat —Select binar y or ASCII.
File Type—Select color or grayscale.
Prev iew—Check to generate a thumbnail image so
that fi le browsers can preview the contents of the
PostScript file.
Page Si ze—Setwidthandheightmeasurements.
Resolution—Setwidthandheightresolutionin
dots per inch (dpi).
GIF Files
GIF is an 8-bit (256-color) format developed
by Informix for the CompuServe
®
information
service. It was originally designed to minimize file
transfer times over telephone lines.
GIF is supported only as an input file format. You
can use GIF files as general-purpose bitmaps, but
you can’t render to a GIF fi le.
HDR I Files
HDRI is a file format used for hig h-dynamic-range
images. Most cameras don’t have the capability
to capture the dynamic range (the gamut of
luminances between dark and bright regions) that
is present in the real world. However, the range
can be recovered by ta king a ser ies of pictures of
thesamesubjectwithdifferentexposuresettings,
and combining them into one image file.
This type of image is called a high dynamic range
image (HDRI) or radiance map.HDRIfileshave
an .hdr extension and radiance maps have a .pic
extension. The file actually contains all the data
from all the pictures, so a wide luminance range
is present, from bright, white highlights to the
darkest black.
HDR fi les are particularly useful as backgrounds
for compositing, and as reflection maps on
composited objects. When using a HDR image
as a sky light, use the p a rameters in the Exposure
group to control the brightness of the scene.
Procedure
To use a HDR image as a background, or as a diffuse
or r ef l ecti on ma p:
1.
In the Material Editor, choose Bitmap as the
map t ype.
2. On the Select Bitmap Image File dialog, under
Files Of Type, choose Radiance Image File
(HDRI). Open the HDR file you would want
to use.
TheHDRILoadSettingsdialogappears,with
the image displayed in its preview window.
3. On the HDRI Load Settings dialog, look at the
Measured Min/Max values to see the luminance
rangefortheimage.
4. Turn on Black Point.
5. AdjusttheBlackPointandWhitePointvalues
until the red lines on the histogram encompass