[magick-users] histogram and PerlMagick

[Ron Savage]

On Wed, 1 Nov 2006 19:42:05 -0700, Brian Jackson wrote:

Hi Brian

> convert image.jpg -channel red histogram:-|convert - red.png

Here's a program which outputs the same data as above. The vertical scale is 
different, though.

-----><8-----
#!/usr/bin/perl
#
# Note:
#	tab = 4 spaces or die.

use strict;
use warnings;

use Config;
use Image::Magick;

# ----------------

print "Perl V $Config{'version'}. \n";
print "Image::Magick V $Image::Magick::VERSION. \n";

my($old_image)	= Image::Magick -> new();
my($old_name)	= 'ag000602.png';

print "Reading old file: $old_name... \n";

my($result) = $old_image -> Read($old_name);
die $result if $result;

print "Read old file: $old_name. \n";
print "Getting width and height... \n";

my(@detail) = $old_image -> Get('width', 'height');

print "Size: $detail[0] x $detail[1]. Pixel count: @{[$detail[0] * $detail[1] 
]}. \n";
print "Getting histogram... \n";

my(@histogram) = $old_image -> Histogram();

print "Elements in histogram array: @{[scalar @histogram]}. \n";

my($max_pixel_count)	= 0;
my($total_pixel_count)	= 0;
my(@color)				= qw/red green blue/;
my($bit_count)			= 9;
my($power_of_2)			= 2 ** $bit_count;

print "Bit count: $bit_count. Power of 2: $power_of_2. \n";

my(%color, $count, %count);
my($opacity);
my($rgb);

$count{$_} = [(0) x 256] for (@color);

while (@histogram)
{
	($color{'red'}, $color{'green'}, $color{'blue'}, $opacity, $count) = 
splice(@histogram, 0, 5);

	$count{$_}[$color{$_} >> $bit_count]	+= $count for (@color);
	$max_pixel_count						= $count if ($count > $max_pixel_count);
	$total_pixel_count						+= $count;

	#print sprintf "Red: 0x%04x. Green: 0x%04x. Blue: 0x%04x. Opacity: 0x%04x. 
Count: %10i. \n", $color{'red'}, $color{'green'}, $color{'blue'}, $opacity, 
$count;
}

print "Max pixel count:   $max_pixel_count. \n";
print "Total pixel count: $total_pixel_count. \n";

my($x);

=pod

print "Counts: \n";
print 'index', join('  ', map{sprintf '%8s', $_} @color), "\n";

for $x (0 .. 255)
{
	print sprintf '%5i', $x;
	print join('  ', map{sprintf '%8i', int($count{$_}[$x] / $power_of_2)} @color);
	print "\n";
}

=cut

print "Creating images of size: 256 x $power_of_2. \n";

my($image);

for $rgb (@color)
{
	$image	= Image::Magick -> new(size => "256x$power_of_2");
	$result	= $image -> Read('xc:black');
	die $result if $result;

	for $x (0 .. 255)
	{
		$count	= int($count{$rgb}[$x] / $power_of_2);
		$result	= $image -> Set("pixel[$x, @{[$power_of_2 - $_]}]" => $rgb) for (0 .. 
$count);
		die $result if $result;
	}

	$result = $image -> Write("$rgb.png");
	die $result if $result;

	print "Wrote $rgb.png. \n";
}
-----><8-----

-- 
Cheers
Ron Savage, ron at savage.net.au on 7/11/2006
http://savage.net.au/index.html
Let the record show: Microsoft is not an Australian company