Rebol R3 skeleton

Using erode and dilate is similar to OpenCV morphologyEx (not supported by Rebol 3) 

#!/usr/local/bin/r3
Rebol [
]
;--all images are binary with 1 channel
;--using erode and dilate is similar to OpenCV morphologyEx (not supported by Rebol 3)
cv: import opencv
with cv [
    img: imread/with "../images/char.png" IMREAD_GRAYSCALE ;--source image as GS
    threshold :img :img 127 255 THRESH_BINARY ;--binary thresholding
    namedWindow win1: "Source"
    moveWindow win1 0x0
    imshow/name img "Source"
    skel: Matrix [:img/size CV_8UC1] ;--1 channel matrix (8-bit)
    element: getStructuringElement MORPH_CROSS 3x3 -1x-1 ;--structuring element for the kernel
    until [
    eroded: erode :img none element -1x-1 1 ;--erode
    temp: dilate :eroded none element -1x-1 1 ;--then dilate
    subtract :img :temp :temp ;--img source - eroded image
    bitwise-or :skel :temp :skel ;--just OR operator
    img: :eroded ;--update source image
    maxi: second minMaxLoc img ;--get maxi value
    maxi = 0 ;--repeat until maxi = 0
    ]
    namedWindow win2: "Skeleton"
    moveWindow win2 250x0
    imshow/name skel win2
    waitKey 0
    destroyAllWindows
]