ras_palette
Format descriptions for palette files for NCAR Graphics translators.
Synopsis
palette_file.pal
palette_file.txt
Description
NCAR View supports a binary as well as a textual format for color
palettes.
The binary format is compatible with NCSA HDF and must have a file
extension of ".pal". The palette has a red, a green, and a blue table,
each with 256 single unsigned byte entries. A 0 represents no
intensity for a given color, and a 255 full intensity. In the file,
the palette is stored as:
R0 R1 ... R255 G0 G1 ... G255 B0 B1 ... B255
for a total of 768 bytes.
The textual format can be created by a program or manually with a text
editor. It provides for 256 RGB entries but also allows for a sparse
color table. In the latter case, missing values are calculated from
those provided using linear interpolation. If unspecified, the 0 entry
defaults to black and the 255 entry to white. Each color palette
entry has the following format:
index_number red green blue
where index_number, red, green, and
blue are all integers in the range 0 to 255.
Examples
All of the examples below deal with textual color palettes.
Setting Entries
Set color index 0 to black.
0 0 0 0
Set color index 255 to white
255 255 255 255
Grayscale Ramp
Let's suppose you have a file named "my.txt" and it has just two lines
in it: the black entry and the white entry from above. This will
produce a grayscale color palette, where the table starts at black and
ramps up to white; since only entries 0 and 255 are specified, the
remaining indicies are interpolated.
0 0 0 0
255 255 255 255
(Note: An empty palette file (e.g. "empty.txt") is legal and,
since the 0 index defaults to black and the 255 index to white,
produces a grayscale ramp just as in the above example.)
Temperature Color Scale
Let's suppose you want entry 0 to be black, and the remaining indices
to start at 1 with a fully-saturated blue and shift linearly to 255
with a fully-saturated red. Only three entries are required in your
file, "temp.txt".
0 0 0 0
1 0 0 255
255 255 0 0
See also
rasview, rascat,
rasgetpal, rassplit, rasls, ras_formats
Bugs/caveats
Color palettes are only useful with indexed-color imagery.
Copyright
Copyright © 1987-1999
University Corporation for Atmospheric Research
The use of this
software and documentation is governed by a License Agreement.