Bitmap/Flood fill: Difference between revisions
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Note that this does not make any attempt to smoothly fill 'banks' or have a tolerance it matches exact colors only. This will fill the example image with red inside green: |
Note that this does not make any attempt to smoothly fill 'banks' or have a tolerance; it matches exact colors only. This will fill the example image with red inside green: |
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<lang e>{ |
<lang e>{ |
Revision as of 18:22, 26 July 2009
You are encouraged to solve this task according to the task description, using any language you may know.
Implement a flood fill.
A flood fill is a way of filling an area using color banks to define the contained area or a target color which "determines" the area (the valley that can be flooded; Wikipedia uses the term target color). It works almost like a water flooding from a point towards the banks (or: inside the valley): if there's a hole in the banks, the flood is not contained and all the image (or all the "connected valleys") get filled.
To accomplish the task, you need implementing just one of the possible algorithms (examples are on Wikipedia). Variations on the theme are allowed (e.g. adding a tolerance parameter or argument for color-matching of the banks or target color).
Testing: the basic algorithm is not suitable for truecolor images; a possible test image is the one shown on the right box; you can try to fill the white area, or the black inner circle.
Ada
<lang ada> procedure Flood_Fill
( Picture : in out Image; From : Point; Fill : Pixel; Replace : Pixel; Distance : Luminance := 20 ) is function Diff (A, B : Luminance) return Luminance is pragma Inline (Diff); begin if A > B then return A - B; else return B - A; end if; end Diff;
function "-" (A, B : Pixel) return Luminance is pragma Inline ("-"); begin return Luminance'Max (Luminance'Max (Diff (A.R, B.R), Diff (A.G, B.G)), Diff (A.B, B.B)); end "-"; procedure Column (From : Point); procedure Row (From : Point);
Visited : array (Picture'Range (1), Picture'Range (2)) of Boolean := (others => (others => False));
procedure Column (From : Point) is X1 : Positive := From.X; X2 : Positive := From.X; begin Visited (From.X, From.Y) := True; for X in reverse Picture'First (1)..From.X - 1 loop exit when Visited (X, From.Y); declare Color : Pixel renames Picture (X, From.Y); begin Visited (X, From.Y) := True; exit when Color - Replace > Distance; Color := Fill; X1 := X; end; end loop; for X in From.X + 1..Picture'Last (1) loop exit when Visited (X, From.Y); declare Color : Pixel renames Picture (X, From.Y); begin Visited (X, From.Y) := True; exit when Color - Replace > Distance; Color := Fill; X2 := X; end; end loop; for X in X1..From.X - 1 loop Row ((X, From.Y)); end loop; for X in From.X + 1..X2 loop Row ((X, From.Y)); end loop; end Column;
procedure Row (From : Point) is Y1 : Positive := From.Y; Y2 : Positive := From.Y; begin Visited (From.X, From.Y) := True; for Y in reverse Picture'First (2)..From.Y - 1 loop exit when Visited (From.X, Y); declare Color : Pixel renames Picture (From.X, Y); begin Visited (From.X, Y) := True; exit when Color - Replace > Distance; Color := Fill; Y1 := Y; end; end loop; for Y in From.Y + 1..Picture'Last (2) loop exit when Visited (From.X, Y); declare Color : Pixel renames Picture (From.X, Y); begin Visited (From.X, Y) := True; exit when Color - Replace > Distance; Color := Fill; Y2 := Y; end; end loop; for Y in Y1..From.Y - 1 loop Column ((From.X, Y)); end loop; for Y in From.Y + 1..Y2 loop Column ((From.X, Y)); end loop; end Row;
Color : Pixel renames Picture (From.X, From.Y);
begin
if Color - Replace <= Distance then Visited (From.X, From.Y) := True; Color := Fill; Column (From); end if;
end Flood_Fill; </lang> The procedure has the following parameters. Picture is the image to change. From is the point to start at. Fill is the color to fill with. Replace is the color to replace. Distance defines the range of color around Replace to replace as well. The distance is defined as a maximum of the differences of stimuli. The following code snippet reads the test file, fills the area between two circles red, and writes the result: <lang ada> declare
File : File_Type;
begin
Open (File, In_File, "Unfilledcirc.ppm"); declare Picture : Image := Get_PPM (File); begin Close (File); Flood_Fill ( Picture => Picture, From => (122, 30), Fill => (255,0,0), Replace => White ); Create (File, Out_File, "Filledcirc.ppm"); Put_PPM (File, Picture); Close (File); end;
end; </lang>
C
The sys/queue.h
is not POSIX. (See FIFO)
<lang c>/* #include <sys/queue.h> */ typedef struct {
color_component red, green, blue;
} rgb_color; typedef rgb_color *rgb_color_p;
void floodfill(image img, int px, int py, rgb_color_p bankscolor, rgb_color_p rcolor);</lang>
<lang c>#include "imglib.h"
typedef struct _ffill_node {
int px, py; TAILQ_ENTRY(_ffill_node) nodes;
} _ffill_node_t; TAILQ_HEAD(_ffill_queue_s, _ffill_node); typedef struct _ffill_queue_s _ffill_queue;
inline void _ffill_removehead(_ffill_queue *q) {
_ffill_node_t *n = q->tqh_first; if ( n != NULL ) { TAILQ_REMOVE(q, n, nodes); free(n); }
}
inline void _ffill_enqueue(_ffill_queue *q, int px, int py) {
_ffill_node_t *node; node = malloc(sizeof(_ffill_node_t)); if ( node != NULL ) { node->px = px; node->py = py; TAILQ_INSERT_TAIL(q, node, nodes); }
}
inline double color_distance( rgb_color_p a, rgb_color_p b ) {
return sqrt( (double)(a->red - b->red)*(a->red - b->red) +
(double)(a->green - b->green)*(a->green - b->green) + (double)(a->blue - b->blue)*(a->blue - b->blue) ) / (256.0*sqrt(3.0)); }
inline void _ffill_rgbcolor(image img, rgb_color_p tc, int px, int py) {
tc->red = GET_PIXEL(img, px, py)[0]; tc->green = GET_PIXEL(img, px, py)[1]; tc->blue = GET_PIXEL(img, px, py)[2];
}
- define NSOE(X,Y) do { \
if ( ((X)>=0)&&((Y)>=0) && ((X)<img->width)&&((Y)<img->height)) { \ _ffill_rgbcolor(img, &thisnode, (X), (Y)); \ if ( color_distance(&thisnode, bankscolor) > tolerance ) { \
if (color_distance(&thisnode, rcolor) > 0.0) { \ put_pixel_unsafe(img, (X), (Y), rcolor->red, \ rcolor->green, \ rcolor->blue); \ _ffill_enqueue(&head, (X), (Y)); \ pixelcount++; \ } \
} \ } \ } while(0)
unsigned int floodfill(image img, int px, int py,
rgb_color_p bankscolor,
rgb_color_p rcolor)
{
_ffill_queue head; rgb_color thisnode; unsigned int pixelcount = 0; double tolerance = 0.05;
if ( (px < 0) || (py < 0) || (px >= img->width) || (py >= img->height) ) return;
TAILQ_INIT(&head);
_ffill_rgbcolor(img, &thisnode, px, py); if ( color_distance(&thisnode, bankscolor) <= tolerance ) return;
_ffill_enqueue(&head, px, py); while( head.tqh_first != NULL ) { _ffill_node_t *n = head.tqh_first; _ffill_rgbcolor(img, &thisnode, n->px, n->py); if ( color_distance(&thisnode, bankscolor) > tolerance ) { put_pixel_unsafe(img, n->px, n->py, rcolor->red, rcolor->green, rcolor->blue); pixelcount++; } int tx = n->px, ty = n->py; _ffill_removehead(&head); NSOE(tx - 1, ty); NSOE(tx + 1, ty); NSOE(tx, ty - 1); NSOE(tx, ty + 1); } return pixelcount;
}</lang>
The pixelcount could be used to know the area of the filled region. The internal parameter tolerance
can be tuned to cope with antialiasing, bringing "sharper" resuts.
Usage example
(Comments show changes to fill the white area instead of the black circle)
<lang c>#include <stdio.h>
- include <stdlib.h>
- include "imglib.h"
int main(int argc, char **argv) {
image animage; rgb_color ic; rgb_color rc;
if ( argc > 1 ) { animage = read_image(argv[1]); if ( animage != NULL ) { ic.red = 255; /* = 0; */ ic.green = 255; /* = 0; */ ic.blue = 255; /* = 0; */ rc.red = 0; rc.green = 255; rc.blue = 0; floodfill(animage, 100, 100, &ic, &rc); /* 150, 150 */ print_jpg(animage, 90); free(animage); } } return 0;
}</lang>
E
Using the image type from Basic bitmap storage#E.
<lang e>def floodFill(image, x, y, newColor) {
def matchColor := image[x, y] def w := image.width() def h := image.height() /** For any given pixel x,y, this algorithm first fills a contiguous horizontal line segment of pixels containing that pixel, then recursively scans the two adjacent rows over the same horizontal interval. Let this be invocation 0, and the immediate recursive invocations be 1, 2, 3, ..., # be pixels of the wrong color, and * be where each scan starts; the fill ordering is as follows: --------------##########------- -...1111111111*11####*33333...- ###########000*000000000000...- -...2222222222*22222##*4444...- --------------------##--------- Each invocation returns the x coordinate of the rightmost pixel it filled, or x0 if none were. Since it is recursive, this algorithm is unsuitable for large images with small stacks. */ def fillScan(var x0, y) { if (y >= 0 && y < h && x0 >= 0 && x0 < w) { image[x0, y] := newColor var x1 := x0 # Fill rightward while (x1 < w - 1 && image.test(x1 + 1, y, matchColor)) { x1 += 1 image[x1, y] := newColor # This could be replaced with a horizontal-line drawing operation } # Fill leftward while (x0 > 0 && image.test(x0 - 1, y, matchColor)) { x0 -= 1 image[x0, y] := newColor } if (x0 > x1) { return x0 } # Filled at most center
# x0..x1 is now a run of newly-filled pixels. # println(`Filled $y $x0..$x1`) # println(image) # Scan the lines above and below for ynext in [y - 1, y + 1] { if (ynext >= 0 && ynext < h) { var x := x0 while (x <= x1) { if (image.test(x, ynext, matchColor)) { x := fillScan(x, ynext) } x += 1 } } } return x1 } else { return x0 } }
fillScan(x, y)
}</lang>
Note that this does not make any attempt to smoothly fill 'banks' or have a tolerance; it matches exact colors only. This will fill the example image with red inside green:
<lang e>{
println("Read") def i := readPPM(<import:java.io.makeFileInputStream>(<file:Unfilledcirc.ppm>)) println("Fill 1") floodFill(i, 100, 100, makeColor.fromFloat(1, 0, 0)) println("Fill 2") floodFill(i, 200, 200, makeColor.fromFloat(0, 1, 0)) println("Write") i.writePPM(<import:java.io.makeFileOutputStream>(<file:Filledcirc.ppm>)) println("Done")
}</lang>
Forth
This simple recursive algorithm uses routines from Basic bitmap storage. <lang forth>
- third 2 pick ;
- 3dup third third third ;
- 4dup 2over 2over ;
- flood ( color x y bmp -- )
3dup b@ >r ( R: color to fill ) 4dup b! third 0 > if rot 1- -rot 3dup b@ r@ = if recurse then rot 1+ -rot then third 1+ over bwidth < if rot 1+ -rot 3dup b@ r@ = if recurse then rot 1- -rot then over 0 > if swap 1- swap 3dup b@ r@ = if recurse then swap 1+ swap then over 1+ over bheight < if swap 1+ swap 3dup b@ r@ = if recurse then swap 1- swap then r> drop ;
</lang>
Fortran
Here the target color paradigm is used. Again the matchdistance
parameter can be tuned to ignore small differences that could come because of antialiasing.
<lang fortran>module RCImageArea
use RCImageBasic use RCImagePrimitive implicit none
real, parameter, private :: matchdistance = 0.2
private :: northsouth, eastwest
contains
subroutine northsouth(img, p0, tcolor, fcolor) type(rgbimage), intent(inout) :: img type(point), intent(in) :: p0 type(rgb), intent(in) :: tcolor, fcolor
integer :: npy, spy, y type(rgb) :: pc
npy = p0%y - 1 do if ( inside_image(img, p0%x, npy) ) then call get_pixel(img, p0%x, npy, pc) if ( ((pc .dist. tcolor) > matchdistance ) .or. ( pc == fcolor ) ) exit else exit end if npy = npy - 1 end do npy = npy + 1 spy = p0%y + 1 do if ( inside_image(img, p0%x, spy) ) then call get_pixel(img, p0%x, spy, pc) if ( ((pc .dist. tcolor) > matchdistance ) .or. ( pc == fcolor ) ) exit else exit end if spy = spy + 1 end do spy = spy - 1 call draw_line(img, point(p0%x, spy), point(p0%x, npy), fcolor) do y = min(spy, npy), max(spy, npy) if ( y == p0%y ) cycle call eastwest(img, point(p0%x, y), tcolor, fcolor) end do end subroutine northsouth
subroutine eastwest(img, p0, tcolor, fcolor) type(rgbimage), intent(inout) :: img type(point), intent(in) :: p0 type(rgb), intent(in) :: tcolor, fcolor
integer :: npx, spx, x type(rgb) :: pc
npx = p0%x - 1 do if ( inside_image(img, npx, p0%y) ) then call get_pixel(img, npx, p0%y, pc) if ( ((pc .dist. tcolor) > matchdistance ) .or. ( pc == fcolor ) ) exit else exit end if npx = npx - 1 end do npx = npx + 1 spx = p0%x + 1 do if ( inside_image(img, spx, p0%y) ) then call get_pixel(img, spx, p0%y, pc) if ( ((pc .dist. tcolor) > matchdistance ) .or. ( pc == fcolor ) ) exit else exit end if spx = spx + 1 end do spx = spx - 1 call draw_line(img, point(spx, p0%y), point(npx, p0%y), fcolor) do x = min(spx, npx), max(spx, npx) if ( x == p0%x ) cycle call northsouth(img, point(x, p0%y), tcolor, fcolor) end do end subroutine eastwest
subroutine floodfill(img, p0, tcolor, fcolor) type(rgbimage), intent(inout) :: img type(point), intent(in) :: p0 type(rgb), intent(in) :: tcolor, fcolor type(rgb) :: pcolor
if ( .not. inside_image(img, p0%x, p0%y) ) return call get_pixel(img, p0%x, p0%y, pcolor) if ( (pcolor .dist. tcolor) > matchdistance ) return
call northsouth(img, p0, tcolor, fcolor) call eastwest(img, p0, tcolor, fcolor) end subroutine floodfill
end module RCImageArea</lang>
Usage example excerpt (which on the test image will fill with green the inner black circle):
<lang fortran> call floodfill(animage, point(100,100), rgb(0,0,0), rgb(0,255,0))</lang>
Perl
The fill of the Perl package Image::Imlib2 is a flood fill (so the documentatin of Image::Imlib2 says). The target colour is the one of the starting point pixel; the color set with set_color is the fill colour.
<lang perl>#! /usr/bin/perl
use strict; use Image::Imlib2;
my $img = Image::Imlib2->load("Unfilledcirc.jpg"); $img->set_color(0, 255, 0, 255); $img->fill(100,100); $img->save("filledcirc.jpg"); exit 0;</lang>
A homemade implementation can be:
<lang perl>use strict; use Image::Imlib2;
sub colordistance {
my ( $c1, $c2 ) = @_;
my ( $r1, $g1, $b1 ) = @$c1; my ( $r2, $g2, $b2 ) = @$c2; return sqrt(( ($r1-$r2)**2 + ($g1-$g2)**2 + ($b1-$b2)**2 ))/(255.0*sqrt(3.0));
}
sub floodfill {
my ( $img, $x, $y, $r, $g, $b ) = @_; my $distparameter = 0.2;
my %visited = (); my @queue = ();
my @tcol = ( $r, $g, $b ); my @col = $img->query_pixel($x, $y); if ( colordistance(\@tcol, \@col) > $distparameter ) { return; } push @queue, [$x, $y]; while ( scalar(@queue) > 0 ) {
my $pointref = shift(@queue); ( $x, $y ) = @$pointref; if ( ($x < 0) || ($y < 0) || ( $x >= $img->width ) || ( $y >= $img->height ) ) { next; } if ( ! exists($visited{"$x,$y"}) ) { @col = $img->query_pixel($x, $y); if ( colordistance(\@tcol, \@col) <= $distparameter ) { $img->draw_point($x, $y); $visited{"$x,$y"} = 1; push @queue, [$x+1, $y]; push @queue, [$x-1, $y]; push @queue, [$x, $y+1]; push @queue, [$x, $y-1]; } }
}
}
- usage example
my $img = Image::Imlib2->load("Unfilledcirc.jpg"); $img->set_color(0,255,0,255); floodfill($img, 100,100, 0, 0, 0); $img->save("filledcirc1.jpg"); exit 0;</lang>
This fills better than the Image::Imlib2 fill function the inner circle, since because of JPG compression and thanks to the $distparameter, it "sees" as black also pixel that are no more exactly black.
Tcl
Using struct::queue
package from
Using code from Basic bitmap storage#Tcl, Bresenham's line algorithm#Tcl and Midpoint circle algorithm#Tcl <lang tcl>package require Tcl 8.5 package require Tk package require struct::queue
proc floodFill {img colour point} {
set new [colour2rgb $colour] set old [getPixel $img $point] struct::queue Q Q put $point while {[Q size] > 0} { set p [Q get] if {[getPixel $img $p] eq $old} { set w [findBorder $img $p $old west] set e [findBorder $img $p $old east] drawLine $img $new $w $e set q $w while {[x $q] <= [x $e]} { set n [neighbour $q north] if {[getPixel $img $n] eq $old} {Q put $n} set s [neighbour $q south] if {[getPixel $img $s] eq $old} {Q put $s} set q [neighbour $q east] } } } Q destroy
}
proc findBorder {img p colour dir} {
set lookahead [neighbour $p $dir] while {[getPixel $img $lookahead] eq $colour} { set p $lookahead set lookahead [neighbour $p $dir] } return $p
}
proc x p {lindex $p 0} proc y p {lindex $p 1}
proc neighbour {p dir} {
lassign $p x y switch -exact -- $dir { west {return [list [incr x -1] $y]} east {return [list [incr x] $y]} north {return [list $x [incr y -1]]} south {return [list $x [incr y]]} }
}
proc colour2rgb {color_name} {
foreach part [winfo rgb . $color_name] { append colour [format %02x [expr {$part >> 8}]] } return #$colour
}
set img [newImage 70 50] fill $img white
drawLine $img blue {0 0} {0 25} drawLine $img blue {0 25} {35 25} drawLine $img blue {35 25} {35 0} drawLine $img blue {35 0} {0 0} floodFill $img yellow {3 3}
drawCircle $img black {35 25} 24 drawCircle $img black {35 25} 10 floodFill $img orange {34 5} floodFill $img red {36 5}
toplevel .flood label .flood.l -image $img pack .flood.l </lang> Results in: