How to Turn Raster Image into Black & White with Outlines?

Code:
; FU_sketch_sketch-drawing.scm

; version 2.9 [gimphelp.org]

; last modified/tested by Paul Sherman

; 02/15/2014 on GIMP-2.8.10

;

; 02/15/2014  - accommodated indexed images, option tyo flatten upon completion

; (and made flatten default)

;==============================================================

;

; Installation:

; This script should be placed in the user or system-wide script folder.

;

;    Windows Vista/7/8)

;    C:\Program Files\GIMP 2\share\gimp\2.0\scripts

;    or

;    C:\Users\YOUR-NAME\.gimp-2.8\scripts

;    

;    Windows XP

;    C:\Program Files\GIMP 2\share\gimp\2.0\scripts

;    or

;    C:\Documents and Settings\yourname\.gimp-2.8\scripts   

;    

;    Linux

;    /home/yourname/.gimp-2.8/scripts  

;    or

;    Linux system-wide

;    /usr/share/gimp/2.0/scripts

;

;==============================================================

;

; LICENSE

;

;    This program is free software: you can redistribute it and/or modify

;    it under the terms of the GNU General Public License as published by

;    the Free Software Foundation, either version 3 of the License, or

;    (at your option) any later version.

;

;    This program is distributed in the hope that it will be useful,

;    but WITHOUT ANY WARRANTY; without even the implied warranty of

;    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

;    GNU General Public License for more details.

;

;    You should have received a copy of the GNU General Public License

;    along with this program.  If not, see <http://www.gnu.org/licenses/>.

;

;==============================================================

; Original information 

; 

; Drawing script  for GIMP 2.2

; Copyright (C) 2007 Eddy Verlinden <eddy_verlinden@hotmail.com>

;==============================================================





(define (FU-drawing

        img

        drawable

        thickness

        inFlatten

    )



  (gimp-image-undo-group-start img)

  (define indexed (car (gimp-drawable-is-indexed drawable)))

    (if (= indexed TRUE)(gimp-image-convert-rgb img))

    

  (let* (

     (width (car (gimp-drawable-width drawable)))

     (height (car (gimp-drawable-height drawable)))

     (old-selection (car (gimp-selection-save img)))

         (thf (* height  0.005 thickness ))

     (image-type (car (gimp-image-base-type img)))

     (layer-type (car (gimp-drawable-type drawable)))

     (layer-temp1 (car (gimp-layer-new img width height layer-type "temp1"  100 NORMAL-MODE)))

     (layer-temp2 (car (gimp-layer-new img width height layer-type "temp2"  100 NORMAL-MODE)))

        ) 



    (if (eqv? (car (gimp-selection-is-empty img)) TRUE)

        (gimp-drawable-fill old-selection WHITE-IMAGE-FILL)) ; so Empty and All are the same.

    (gimp-selection-none img)

    (gimp-image-insert-layer img layer-temp1 0 -1)

    (gimp-image-insert-layer img layer-temp2 0 -1)

    (gimp-edit-copy drawable)

    (gimp-floating-sel-anchor (car (gimp-edit-paste layer-temp1 0)))



    (if (eqv? (car (gimp-drawable-is-gray drawable)) FALSE)      

        (gimp-desaturate layer-temp1))

    (gimp-edit-copy layer-temp1)

    (gimp-floating-sel-anchor (car (gimp-edit-paste layer-temp2 0)))

    (gimp-invert layer-temp2)

    (plug-in-gauss 1 img layer-temp2 thf thf 0)

    (gimp-layer-set-mode layer-temp2 16)

    (gimp-image-merge-down img layer-temp2 0)

    (set! layer-temp1 (car (gimp-image-get-active-layer img)))

    (gimp-levels layer-temp1 0 215 235 1.0 0 255) 



    (gimp-image-select-item img CHANNEL-OP-REPLACE old-selection)

    (gimp-selection-invert img)

    (if (eqv? (car (gimp-selection-is-empty img)) FALSE) ; both Empty and All are denied

        (begin

        (gimp-edit-clear layer-temp1)

        ))



    (gimp-item-set-name layer-temp1 "Drawing")

    (gimp-image-select-item img CHANNEL-OP-REPLACE old-selection)

    (gimp-image-remove-channel img old-selection)



    (if (= inFlatten TRUE)(gimp-image-flatten img))

    (gimp-image-undo-group-end img)

    (gimp-displays-flush)

  )

)



(script-fu-register

    "FU-drawing"

    "<Image>/Script-Fu/Sketch/Drawing"

    "Creates a drawing.\n\nThis version lets you adjust the line thickness."

    "Eddy Verlinden <eddy_verlinden@hotmail.com>"

    "Eddy Verlinden"

    "2007, juli"

    "*"

    SF-IMAGE      "Image"                            0

    SF-DRAWABLE   "Drawable"                        0

    SF-ADJUSTMENT "thickness"                        '(2 1 5 1 1 0 0)

    SF-TOGGLE     "Flatten image when complete?"     TRUE

)