Flood-Fill. Flood-fill. Flood-Fill from Seed. Recursive Flood-Fill. 8-connected vs. 4-connected. Recursive Flood-Fill Algorithm

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1 Flood-fill Flood-Fill Used in interctive pint systems. The user specify seed by pointing to the interior of the region to initite flood opertion Recursive Flood-Fill Fill imge-spce region with some intensity (color) vlue How to define the region? Fill Until vs. Fill While 4-connectivity vs. 8-connectivity Flood-Fill from eed trt from the seed nd floods the region until boundry is met. simple recursive lgorithm cn be used: void floodfill(int x, int y, int fill, int old) if (getpixel(x, y) == old) setpixel(fill, x, y); floodfill(x+1, y, fill, old); floodfill(x, y+1, fill, old); floodfill(x-1, y, fill, old); floodfill(x, y-1, fill, old); 8-connected vs. 4-connected Recursive Flood-Fill lgorithm The lgorithm is very simple, however it is: n 8-connected flood is ble to flood through corners tht 4-connected flood cnnot. highly recursive - requiring huge number of procedurl clls; cn cuse recursion stck to overflow no mechnism to determine whether the visited pixels hve been tested before 1

Fill Until vs. Fill While 4-connectivity vs. 8-connectivity Flood-Fill from eed trt from the seed nd floods the region until boundry is met.

2 Fill Until vs. Fill While Flood Until seed void flooduntil(int x, int y, int n_color, int _color) c = getpixel(x, y); if (c!= n_color && c!= _color) setpixel(new_color, x, y); floodfill(x+1, y, n_color _color); floodfill(x, y+1, n_color _color); floodfill(x-1, y, n_color _color); floodfill(x, y-1, n_color _color); Flood While With globl vribles void floodwhile(int x, int y, int n_color, int old) if (getpixel(x, y) == old) setpixel(fill, x, y); floodfill(x+1, y, n_color, old); floodfill(x, y+1, n_color, old); floodfill(x-1, y, n_color, old); floodfill(x, y-1, n_color, old); void floodwhile(int x, int y) if (getpixel(x, y) == old_color) setpixel(n_color, x, y); floodfill(x+1, y); floodfill(x, y+1); floodfill(x-1, y); floodfill(x, y-1); Use stck Queue q = Ø dd the seed to q While(!q.empty()) P = q.pop(); For (x = P s neighboring pixels) If (getpixel(x) == old) setpixel(x, new_color); q.push(x); :KLOHYV8QWLO procedure FloodWhile (x,y: integer; oldvl, nwvl: color); if RedPixel (x,y) = oldvl then WritePixel (x, y, newvl); FloodWhile (x, y-1, oldvl, newvl); FloodWhile (x, y+1, oldvl, newvl); FloodWhile (x-1, y, oldvl, newvl); FloodWhile (x+1, y, oldvl, newvl); procedure FloodUntil (x,y: integer; boundryvl, nwvl: color); vr c: color c:=redpixel (x,y); if (c <> boundryvl) nd ( c <> newvl) then WritePixel (x, y, newvl); FloodUntil (x, y-1, boundryvl, newvl); FloodUntil (x, y+1, boundryvl, newvl); FloodUntil (x-1, y, boundryvl, newvl); FloodUntil (x+1, y, boundryvl, newvl); 2

vribles void floodwhile(int x, int y, int n_color, int old) if (getpixel(x, y) == old) setpixel(fill, x, y); floodfill(x+1, y, n_color, old); floodfill(x, y+1, n_color, old); floodfill(x-1, y,

3 eril Recursion is Depth-First o the fill lgorithm will continue in one direction until boundry is reched. It will then chnge directions momentrily nd ttempt to continue bck in the originl direction. Potentil problem of stck overflow. How to void it? reth-first Trversl Queue q = Ø dd the seed to q While(!q.empty()) P = q.removefirst(); For (x = P s neighboring pixels) If (getpixel(x) == old) setpixel(x, fill); q.insert(x); Recursive Flood-Fill lgorithm Cn lso hve n until version, defining region by boundry Recursive flood-fill is somewht blind nd mny pixels my be retested severl times Tg pixel with direction nd void redundnt clls Row coherence cn improve performnce drmticlly Push ddress of seed pixel onto stck while(stck is not empty) Pop the stck to provide next seed Fill in the run defined by the seed In the djcent rows (bove nd below) find the rechble interior runs, nd push the ddress of their rightmost pixels C C 3

removefirst(); For (x = P s neighboring pixels) If (getpixel(x) == old) setpixel(x, fill); q.

4 D D b 4

5 The then contins:,c,d,f,g b g e d c d c f Flood Fill lgorithm procedure Fill ( x, y : integer; oldvl, newvl: color); push (x, y); while stck is not empty pop (x, y); open_up = FLE; open_down = FLE; while color [x--, y] == oldvl; /* move to most left pixel */ while color [x++,y] == oldvl color [x,y] = newvl; if open_up == FLE if color [x, y+1] == oldvl push (x, y+1); open_up = TRUE; else if color [x, y+1] <> oldvl open_up = FLE; if open_down == FLE if color [x, y-1] == oldvl push (x, y-1); open_down = TRUE; else if color [x, y-1] <> oldvl open_doun = FLE; 5

oldvl color [x,y] = newvl; if open_up == FLE if color [x, y+1] == oldvl push (x, y+1); open_up = TRUE; else if color [x, y+1] <> oldvl

PROF. BOYAN KOSTADINOV NEW YORK CITY COLLEGE OF TECHNOLOGY, CUNY

MAT 0630 INTERNET RESOURCES, REVIEW OF CONCEPTS AND COMMON MISTAKES PROF. BOYAN KOSTADINOV NEW YORK CITY COLLEGE OF TECHNOLOGY, CUNY Contents 1. ACT Compss Prctice Tests 1 2. Common Mistkes 2 3. Distributive