NAME

       ras_palette - format descriptions for palette files for NCAR View

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(1NCARG),rascat(1NCARG),rasgetpal(1NCARG), rassplit(1NCARG),rasls(1NCARG),ras_formats(5NCARG)

BUGS/CAVEATS

       Color palettes are only useful with indexed-color imagery.

COPYRIGHT

       Copyright (C) 1987-2009
       University Corporation for Atmospheric Research

       The use of this Software is governed by a License Agreement.

NCARG                                             January 1993                               RAS_PALETTE(5NCARG)