NAME
Image::Quantize - quantize image data into 256 or fewer colours
SYNOPSIS
use Image::Quantize;DESCRIPTION
Image::Quantize is an interface to the C library "libimagequant".
METHODS
This is an XS module which uses [libimagequant](http://pngquant.org/lib/) to quantize PNG and other images.
All of the PNG handling is done by Image::PNG::Libpng rather than by the code from pngquant, so we just use libimagequant to handle quantization. Because it is not PNG specific, we just call it Image::Quantize and then a subclass Image::Quantize::PNG handles the PNG stuff.
new
Image::Quantize->newcorresponds to `liq_attr_create`. Arguments include
* max_colors * speed * dithering_level * quality * min_opacity * min_posterization
which correspond to the setters described below.
DESTROY calls `liq_attr_destroy`.
set
All setters can be accessed like this:
$quantizer->set (dithering_level => $y);get
All getters can be accessed like this:
my $dl = $quantizer->get ('dithering_level');The above is Perl which accesses the following XS mirrors of libimagequant. I copy the names but `s/^liq_[gs]et_//` and use context to imply set or get.
max_colors
$quantizer->max_colors ($x)calls `liq_set_max_colors`.
quality
$quantizer->quality ($min, $max)calls `liq_set_quality`.
dithering_level
$quantizer->dithering_level ($x)This overrides the default dithering level. The default can be restored with
default_dithering_level
$quantizer->default_dithering_level ();The default dithering depends on the speed chosen. The default speed is 3.
speed
$quantizer->speed ($x)calls `liq_set_speed`. The default speed is 3, and the value of the speed is an integer from 1 to 10.
min_opacity
$quantizer->min_opacity ($x)calls `liq_set_min_opacity`.
min_posterization
$quantizer->min_posterization ($x)calls `liq_set_min_posterization`.
quantization_error
my $qe = $quantizer->quantization_error ()calls `liq_get_quantization_error`.
output_gamma
$quantizer->output_gamma ($x)calls `liq_set_output_gamma`. Called without argument it returns value from `liq_get_output_gamma`, e.g.
my $gamma = $quantizer->output_gamma ();quantize
The main routine looks like this:
my $qpng = $quantizer->quantize ($png);This handles all of the jive to do with getting memory out of the PNG, ensuring that the image is RGBA using libpng transforms, etc. An alternative interface,
quantize_in_place
$quantizer->quantize_in_place ($png);replaces the image data in $png with quantized data.
(unimplemented)
quantize_file
Also
$quantizer->quantize_file (in => 'in.png', out => 'out.png');saves having to think about files, PNG objects etc. for the casual user who wants to quantize a bunch of files.
All of the setters can be added as options after `$png`:
my $qpng = $quantizer->quantize ($png, dithering_level => $y);This just calls the Perl setting routine. I would like to have it so that these were local only to `$png` but libimagequant doesn't seem to provide `liq_get_dithering_level` - maybe hack that into it.
`liq_image_create_rgba` is handled within $quantizer->quantize ();, not user-visible. `liq_quantize_image` is also handled by the quantize method.
`liq_get_palette` is handled within `quantize` method.
set_log_callback
Logging can be handled like
sub do_something
{
my ($message, $user_data) = @_;
}
$quantizer->set_log_callback (\& do_something);and cancelled with
$quantizer->set_log_callback ();Image::Quantize is a base class, and then a subclass Image::Quantize::PNG handles PNG images. No other image types are currently planned. Image::Quantize::PNG is bundled into Image::Quantize, and uses Image::PNG::Libpng objects for reading and writing as shown in the synopsis above.