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        xsize    => $self->xsize,
        ysize    => $self->ysize,
        channels => 4,
    );

    my $matrix  = $self->matrix;

    my ($w, $h) = ($self->xsize, $self->ysize);
    my $max     = max(@{ $matrix });

    unless ($max) {
        carp "Nothing to be rendered";
        return $img;
    }

    my %color_cache;
    for (my $y = 0; $y < $h; $y++) {
        my @linedata = map {
            my $hue   = int((1 - $_/$max)*240);
            my $alpha = int(sqrt($_/$max)*255);

            $color_cache{"$hue $alpha"} ||= Imager::Color->new(
                hue        => $hue,
                saturation => 1.0,
                value      => 1.0,
                alpha      => $alpha,
            );
        } @$matrix[$y*$w..$y*$w+$w-1];

        $img->setscanline('y' => $y, pixels => \@linedata);
    }

    return $img;
}

1;
__END__

=head1 NAME

Imager::Heatmap - Perl extension for drawing Heatmap using Imager

=head1 SYNOPSIS

    use Imager::Heatmap;
    my $hmap = Imager::Heatmap->new(
        xsize  => 640,        # Image width
        ysize  => 480,        # Image height
        xsigma => 10,         # Sigma value of X-direction
        ysigma => 10,         # Sigma value of Y-direction
    );

    # Add point datas to construct density matrix
    $hmap->insert_datas(@piont_datas); # @point_datas should be: ( [ x1, y1, weight1 ], [ x2, y2, weight2 ] ... )

    $hmap->insert_datas(...); # You can call multiple times to add large data that cannot process at a time.

    # After adding datas, you could get heatmap as Imager instance.
    my $img = $hmap->draw;

    # Returned image is 4-channels image. So you can overlay it on other images.
    $base_img->rubthrough( src => $hmap->img );  # Overlay on other images(see Imager::Transformations)

    # And you can access probability density matrix using matrix method if you like.
    # In case, maybe you would like to create some graduations which be assigned to color of heatmap and its value.
    $hmap->matrix;

=head1 DESCRIPTION

Imager::Heatmap is a module to draw heatmap using Imager.

This module calculates probability density matrix from input data and
map a color for each pixels to represent density of input data.

=head1 METHODS

=head2 new()

Create a blessed object of Imager::Heatmap.
You can specify some options as follows.
See the accessors description for more details about each parameters.

    $hmap = Imager::Heatmap->new(xsize => 300, ysize => 300);

=head3 Options

=over

=item o xsize       (required)

X-direction size of heatmap image.
 
=item o ysize       (required)

Y-direction size of heatmap image.

=item o xsigma      (optional, default: 1.0)

Sigma value of X-direction.

=item o ysigma      (optional, default: 1.0)

Sigma value of Y-direction.

=item o correlation (optional, default: 0.0)

Correlation between X and Y.

=back

=head2 xsize()

Set/Get the X-direction size of heatmap image.
Constructed matrix will invalidated after call this method as "Setter".

    $hmap->xsize(100);
    $xsize = $hmap->xsize;

=head2 ysize()

Set/Get the Y-direction size of heatmap image.