Edge Finder

Edge Finding facilities are provided by "vision/edge/edge".

$\begin{emtabbing} {\bf edge1} \it img \=\&optional \=(method 1) \\lq [function]\ ... ...>\&aux (width (send img :width)) (height (send img :height)) \rm \end{emtabbing}$

: finds edge pixels in this image. edge1 first applies a gradient operator to every pixel. There are three kinds of gradient operators provided: grad3 which takes difference between horizontally and vertically neighboring pixels, prewitt and sobel. method=0,1 selects grad3, 2 selects prewitt and 3 selects sobel. Pixels that have edge intensity greater than th1 are identified as strong edge pixels. After thinning edges referring to edge intensities and directions of gradient, isolated edge pixels are marked. Starting from end points of these strong edges, weak edge pixels that are consistent with the strong edge's direction are searched for and linked to compose elongated lines. Weak edge pixels that have greater edge intensity than th2 are unconditionally linked. Even very weak edge pixels that have less edge intensity than th2 can be linked as long as they connect to another weak or strong edge within run length. edge1 returns a pixel-image object each pixel of which represents either a strong edge pixel (=1), a weak and elongated edge pixel (=2), or an isolated pixel (=255).

overlay-edge ximg edgeimg [function]

: displays edgeimg obtained by edge1 on top of x-display-able pixel image ximg. Strong edge pixels are colored in red, weak pixels in green, and isolated pixels in blue.

$\begin{emtabbing} {\bf edge2} \it img1 edge1result \&key \=(kvalue 8.0) \\lq [func... ...) (line-error 2.8)\\ \>(curve-error 2.8) (plane-limit 0.3) \rm \end{emtabbing}$

: tries to fit straight lines and elliptic curves to the result obtained by edge1. A list of three elements, which represents regions, boundaries, and line segments is returned.

Three elements represented by edge2 are defined as follow.

region [class]


  :super   propertied-object 

  :slots 		 contour area intensity std-deviation

: represents region.

boundary [class]


  :super   propertied-object 

  :slots 		 parent-region  hole  segments  intensity  top-left  bottom-right  length

: represents boundary.

edge-segment [class]


  :super   propertied-object 

  :slots 		 prev next   wing ; the other half-edge  intensity std-deviation   start end

: represents edge-segment.

line-edge-segment [class]


  :super   edge-segment 

  :slots 		 la lb

: represents line-edge-segment.

curved-edge-segment [class]


  :super   edge-segment 

  :slots 		 rotation total-rot side   a b c d e

: represents curved-edge-segment.

$\begin{emtabbing} {\bf draw-ellipse-segment} \it elp gc \&optional \=(vs *views... ...*) (height (send vs :height)) \\lq [function]\\ \>(x 0) (y 0) \rm \end{emtabbing}$

: draws curved-edge-segment object elp on xwindow vs.

draw-line-segment s &optional gc (vs *viewsurface*) (height (send vs :height)) (x 0) (y 0) [function]

: draws line-edge-segment object s on xwindow vs.

$\begin{emtabbing} {\bf draw-segments} \it segs \&key \=(line-gc image::*red-gc*... ...*) (height (send vs :height)) (step nil)\\ \>(x 0) (y 0) \rm \end{emtabbing}$

: draws s, a list of edge-segment objects on xwindow vs.

draw-boundary b &optional gc [function]

: draws segments of boundary object b on xwindow vs.

draw-boundaries bs &optional gc (step nil) [function]

: draws segments of boundary objects bs on xwindow vs.

*red-gc* [variable]

: GC whose foreground color is #ff0000

*blue-gc* [variable]

: GC whose foreground color is #0000ff

*green-gc* [variable]

: GC whose foreground color is #00ff00

*yellow-gc* [variable]

: GC whose foreground color is #ffff00

*cyan-gc* [variable]

: GC whose foreground color is #00ffff

**Figure 14:** Edge Finder and Overlaid Edges
$\begin{figure}\begin{center} \mbox{\epsfsize10cm \epsfbox{fig/block1.edg.ps} }\end{center}\end{figure}$

k-okada 2013-05-21