       Image  comments are similar to environment variables. They
       have a name and optional value and are saved along with an
       image.   They  can be used to save human-readable informa-
       tion or data for use by other programs.  RLE  files  store
       comments in a manner were they are retrievable.   Comments
       may also be added to pixmaps.  If a pixmap is then  copied
       to an RLE file, the comments are also copied.  The follow-
       ing comments are added automatically by Tcl-SIPP:

              o TSIPP_VERSION - The Tcl-SIPP version number.

              o TSIPP_IMAGE - Data describing the  image  in  the
              form  of a Tcl list.  The list consists of the fol-
              lowing elements:

                 o The rendering mode: FLAT,  GOURAUD,  PHONG  or
                 LINE.   UNKNOWN24 is used for 24 bit images were
                 the rendering mode is unknown.

                 o The oversampling factor  used  to  render  the
                 image.

                 o  BOTH,  ODD or EVEN, indicates which scanlines
                 are included in the image.

                 o The background color, in the standard Tcl-SIPP
                 format.

                 o  The line color, in the standard Tcl-SIPP for-
                 mat.  This useful only if LINE  mode  is  speci-
                 fied.

              o  HISTORY - A variable containing the command line
              that was used to render the image.  This is a stan-
              dard  RLE comment, all image filters add their com-
              mand lines to the comment, so it serves as  a  his-
              tory of how the image was processed.

       The  following  comments  are  standard to the Utah Raster
       Toolkit.  They are not added by Tcl-SIPP, but it  is  sug-
       gested that you use them.

              o image_gamma - The image gamma.  I have found that
              a value of 0.4 produces getx11  displays  that  are
              similar to the default photo widget displays.

              o image_title - A title for the image.
