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.