[magick-users] histogram and PerlMagick

[Gabe Schaffer]

On 11/3/06, Brian Jackson <brian at actionathletics.com> wrote:

> But when the windos and mac ports happen, then I have to convert my
> shell script to whatever in the hell windos uses for shell scripts.
> Mac, not a problem, it's got bash.  Another reason I want a 100% perl
> solution.

Here's some 100% perl code to do pretty much what you want:

	my $temp;
	$temp = $image->Clone();
	$temp->Modulate("100, 0, 0") unless $bw;
	my @black = Histogram($temp);
	$temp = $image->Clone();
	$temp->Channel("Red");
	my @red = Histogram($temp);
	$temp = $image->Clone();
	$temp->Channel("Green");
	my @green = Histogram($temp);
	$temp = $image->Clone();
	$temp->Channel("Blue");
	my @blue = Histogram($temp, $blackpoint, $whitepoint);

sub Histogram
{
	my ($image) = @_;

	my $filename = "histogram" . rand;
	$image->Write("histogram:$filename");
	undef $image->[0];
	my $hg = new Image::Magick;
	$hg->Read($filename);
	unlink $filename;
	return $hg
}

> Maybe I just need to learn some graphics programming and understand that
> HUGE array that is returned from the Histogram() method  :-D

Is the Historgram() method much faster than what you have now?

> > To use less time, you may want to use a Q8 build because it will only
> > have half the data to process. Also, you should try computing a
> > single color histogram and using the individual channels from it to
> > make the different color histograms.
>
> And actually, computing the histogram first and then trying to extract
> the channels from that...doesn't seem to work for me.  I get 3 black
> files :(

What do you mean by black? Do you mean every pixel is black? Or just
that there are no colored pixels?

> > A third trick would be to resize the image, then compute the
> > historgrams from that. This is a notable idea because that's how
> > Photoshop (and presumably The GIMP) can do it so much faster than
> > ImageMagick.
>
> This is from a reduced image size.  That's how my program can process
> 100's of photos in a few minutes.

Do you resize or resample? The method you use will make a difference.

GNS