


IMG(2)                Standards and Formats                IMG(2)



NAME
     IMG File Format - The IMG file format for use in the  VolVis
     system


DESCRIPTION
     The IMG file format is the format for  image  files  in  the
     VolVis  system.   VolVis  1.0 can currently input and output
     only 24 bit  image  files  (although  these  images  can  be
     displayed  on  an  8 bit monitor).  The format consists of a
     header, followed by the red component of the image, then the
     green  componenet,  then the blue component.  Each component
     may be compressed using a run-length encoding technique,  or
     may  be  uncompressed.  When  an image is saved using VolVis
     1.0, compression is always  attempted.   If  compressing  an
     image would result in an image size greater than it would be
     uncompressed, compression is not used. The system  can  read
     in compressed and uncompressed images.  The exact IMG format
     is as follows:

      byte      size   name            description
      ----------------------------------------------
      0          int  width      the width of the image
                                 in pixels
      4          int  height     the height of the image
                                 in pixels
      8          int  depth      the depth of the image
                                 in bytes (in version 1.0
                                 this will always be a 3)
      12 C_CompressionType ctype the compression type used
                                 on this image - it will be
                                 either C_RUN_LENGTH_ENCODE
                                 or C_NO_COMPRESSION
      16      C_Byte  red        the red information
                                 the size of this depends
                                 on the compression type
      XX      C_Byte  green      the green information
                                 the size of this depends
                                 on the compression type
      YY      C_Byte  blue       the blue information
                                 the size of this depends
                                 on the compression type

     If the compression type is C_NO_COMPRESSION, then  the  size
     of  each of the red, green, and blue components of the image
     will be width*height bytes.   If  the  compression  type  is
     C_RUN_LENGTH_ENCODE,  then  the size of each color component
     is dependent on how well the data compresses.


SEE ALSO
     FUN,   SLC,    TXT,    C_write_IMG_file,    C_read_IMG_file,



VolVis 1.0          Last change: May 17, 1993                   1






IMG(2)                Standards and Formats                IMG(2)



     C_encode_bytes, C_decode_bytes



AUTHOR
          Lisa Sobierajski

















































VolVis 1.0          Last change: May 17, 1993                   2



