Bitmap/Histogram: Difference between revisions
Rename Perl 6 -> Raku, alphabetize, minor clean-up
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Thundergnat (talk | contribs) (Rename Perl 6 -> Raku, alphabetize, minor clean-up) |
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* Find the median: defined as the luminance such that the image has an approximately equal number of pixels with lesser and greater luminance.
* Replace each pixel of luminance lesser than the median to black, and others to white.
Use [[read ppm file | read]]/[[write ppm file]], and [[grayscale image]] solutions.
=={{header|Ada}}==
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ibw( img <= m ) = 0;
jpgwrite("lennamed.jpg", ibw, 100);</lang>
=={{header|Phix}}==
Line 1,343 ⟶ 1,284:
Sorry guys... I just give up on linking/displaying these images any other way!
=={{header|Raku}}==
(formerly Perl 6)
{{works with|Rakudo|2017.09}}
Uses pieces from [[Bitmap#Perl_6| Bitmap]], [[Bitmap/Write_a_PPM_file#Perl_6| Write a PPM file]] and [[Grayscale_image#Perl_6| Grayscale image]] tasks. Included here to make a complete, runnable program.
<lang perl6>class Pixel { has UInt ($.R, $.G, $.B) }
class Bitmap {
has UInt ($.width, $.height);
has Pixel @.data;
}
role PBM {
has @.BM;
method P4 returns Blob {
"P4\n{self.width} {self.height}\n".encode('ascii')
~ Blob.new: self.BM
}
}
sub getline ( $fh ) {
my $line = '#'; # skip comments when reading image file
$line = $fh.get while $line.substr(0,1) eq '#';
$line;
}
sub load-ppm ( $ppm ) {
my $fh = $ppm.IO.open( :enc('ISO-8859-1') );
my $type = $fh.&getline;
my ($width, $height) = $fh.&getline.split: ' ';
my $depth = $fh.&getline;
Bitmap.new( width => $width.Int, height => $height.Int,
data => ( $fh.slurp.ords.rotor(3).map:
{ Pixel.new(R => $_[0], G => $_[1], B => $_[2]) } )
)
}
sub grayscale ( Bitmap $bmp ) {
map { (.R*0.2126 + .G*0.7152 + .B*0.0722).round(1) min 255 }, $bmp.data;
}
sub histogram ( Bitmap $bmp ) {
my @gray = grayscale($bmp);
my $threshold = @gray.sum / @gray;
for @gray.rotor($bmp.width) {
my @row = $_.list;
@row.push(0) while @row % 8;
$bmp.BM.append: @row.rotor(8).map: { :2(($_ X< $threshold)».Numeric.join) }
}
}
my $filename = './Lenna.ppm';
my Bitmap $b = load-ppm( $filename ) but PBM;
histogram($b);
'./Lenna-bw.pbm'.IO.open(:bin, :w).write: $b.P4;</lang>
See [https://github.com/thundergnat/rc/blob/master/img/Lenna.png Lenna], and [https://github.com/thundergnat/rc/blob/master/img/Lenna-bw.png Lenna-bw] images. (converted to .png as .ppm format is not widely supported).
=={{header|Ruby}}==
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