Imager::Filters(3) User Contributed Perl Documentation Imager::Filters(3)NAMEImager::Filters - Entire Image Filtering Operations
SYNOPSIS
use Imager;
$img = ...;
$img->filter(type=>'autolevels');
$img->filter(type=>'autolevels', lsat=>0.2);
$img->filter(type=>'turbnoise')
# and lots of others
load_plugin("dynfilt/dyntest.so")
or die "unable to load plugin\n";
$img->filter(type=>'lin_stretch', a=>35, b=>200);
unload_plugin("dynfilt/dyntest.so")
or die "unable to load plugin\n";
$out = $img->difference(other=>$other_img);
DESCRIPTION
Filters are operations that have similar calling interface.
filter()
Parameters:
· type - the type of filter, see "Types of Filters".
· many other possible parameters, see "Types of Filters" below.
Returns the invocant ($self) on success, returns a false value on
failure. You can call "$self->errstr" to determine the cause of
the failure.
$self->filter(type => $type, ...)
or die $self->errstr;
Types of Filters
Here is a list of the filters that are always available in Imager.
This list can be obtained by running the "filterlist.perl" script that
comes with the module source.
Filter Arguments Default value
autolevels lsat 0.1
usat 0.1
skew 0
bumpmap bump lightx lighty
elevation 0
st 2
bumpmap_complex bump
channel 0
tx 0
ty 0
Lx 0.2
Ly 0.4
Lz -1
cd 1.0
cs 40.0
n 1.3
Ia (0 0 0)
Il (255 255 255)
Is (255 255 255)
contrast intensity
conv coef
fountain xa ya xb yb
ftype linear
repeat none
combine none
super_sample none
ssample_param 4
segments(see below)
gaussian stddev
gradgen xo yo colors
dist 0
hardinvert
hardinvertall
mosaic size 20
noise amount 3
subtype 0
postlevels levels 10
radnoise xo 100
yo 100
ascale 17.0
rscale 0.02
turbnoise xo 0.0
yo 0.0
scale 10.0
unsharpmask stddev 2.0
scale 1.0
watermark wmark
pixdiff 10
tx 0
ty 0
All parameters must have some value but if a parameter has a default
value it may be omitted when calling the filter function.
Every one of these filters modifies the image in place.
If none of the filters here do what you need, the "transform()" in
Imager::Engines or "transform2()" in Imager::Engines function may be
useful.
A reference of the filters follows:
autolevels
scales the value of each channel so that the values in the image
will cover the whole possible range for the channel. "lsat" and
"usat" truncate the range by the specified fraction at the top and
bottom of the range respectively.
# increase contrast per channel, losing little detail
$img->filter(type=>"autolevels")
or die $img->errstr;
# increase contrast, losing 20% of highlight at top and bottom range
$img->filter(type=>"autolevels", lsat=>0.2, usat=>0.2)
or die $img->errstr;
bumpmap
uses the channel "elevation" image "bump" as a bump map on your
image, with the light at ("lightx", "lightty"), with a shadow
length of "st".
$img->filter(type=>"bumpmap", bump=>$bumpmap_img,
lightx=>10, lighty=>10, st=>5)
or die $img->errstr;
bumpmap_complex
uses the channel "channel" image "bump" as a bump map on your
image. If "Lz < 0" the three L parameters are considered to be the
direction of the light. If "Lz > 0" the L parameters are
considered to be the light position. "Ia" is the ambient color,
"Il" is the light color, "Is" is the color of specular highlights.
"cd" is the diffuse coefficient and "cs" is the specular
coefficient. "n" is the shininess of the surface.
$img->filter(type=>"bumpmap_complex", bump=>$bumpmap_img)
or die $img->errstr;
contrast
scales each channel by "intensity". Values of "intensity" < 1.0
will reduce the contrast.
# higher contrast
$img->filter(type=>"contrast", intensity=>1.3)
or die $img->errstr;
# lower contrast
$img->filter(type=>"contrast", intensity=>0.8)
or die $img->errstr;
conv
performs 2 1-dimensional convolutions on the image using the values
from "coef". "coef" should be have an odd length and the sum of
the coefficients must be non-zero.
# sharper
$img->filter(type=>"conv", coef=>[-0.5, 2, -0.5 ])
or die $img->errstr;
# blur
$img->filter(type=>"conv", coef=>[ 1, 2, 1 ])
or die $img->errstr;
# error
$img->filter(type=>"conv", coef=>[ -0.5, 1, -0.5 ])
or die $img->errstr;
fountain
renders a fountain fill, similar to the gradient tool in most paint
software. The default fill is a linear fill from opaque black to
opaque white. The points "A(Cxa, ya)" and "B(xb, yb)" control the
way the fill is performed, depending on the "ftype" parameter:
"linear"
the fill ramps from A through to B.
"bilinear"
the fill ramps in both directions from A, where AB defines the
length of the gradient.
"radial"
A is the center of a circle, and B is a point on it's
circumference. The fill ramps from the center out to the
circumference.
"radial_square"
A is the center of a square and B is the center of one of it's
sides. This can be used to rotate the square. The fill ramps
out to the edges of the square.
"revolution"
A is the center of a circle and B is a point on its
circumference. B marks the 0 and 360 point on the circle, with
the fill ramping clockwise.
"conical"
A is the center of a circle and B is a point on it's
circumference. B marks the 0 and point on the circle, with the
fill ramping in both directions to meet opposite.
The "repeat" option controls how the fill is repeated for some
"ftype"s after it leaves the AB range:
"none"
no repeats, points outside of each range are treated as if they
were on the extreme end of that range.
"sawtooth"
the fill simply repeats in the positive direction
"triangle"
the fill repeats in reverse and then forward and so on, in the
positive direction
"saw_both"
the fill repeats in both the positive and negative directions
(only meaningful for a linear fill).
"tri_both"
as for triangle, but in the negative direction too (only
meaningful for a linear fill).
By default the fill simply overwrites the whole image (unless you
have parts of the range 0 through 1 that aren't covered by a
segment), if any segments of your fill have any transparency, you
can set the combine option to 'normal' to have the fill combined
with the existing pixels. See the description of combine in
Imager::Fill.
If your fill has sharp edges, for example between steps if you use
repeat set to 'triangle', you may see some aliased or ragged edges.
You can enable super-sampling which will take extra samples within
the pixel in an attempt anti-alias the fill.
The possible values for the super_sample option are:
none
no super-sampling is done
grid
a square grid of points are sampled. The number of points
sampled is the square of ceil(0.5 + sqrt(ssample_param)).
random
a random set of points within the pixel are sampled. This
looks pretty bad for low ssample_param values.
circle
the points on the radius of a circle within the pixel are
sampled. This seems to produce the best results, but is fairly
slow (for now).
You can control the level of sampling by setting the ssample_param
option. This is roughly the number of points sampled, but depends
on the type of sampling.
The segments option is an arrayref of segments. You really should
use the Imager::Fountain class to build your fountain fill. Each
segment is an array ref containing:
start
a floating point number between 0 and 1, the start of the range
of fill parameters covered by this segment.
middle
a floating point number between start and end which can be used
to push the color range towards one end of the segment.
end a floating point number between 0 and 1, the end of the range
of fill parameters covered by this segment. This should be
greater than start.
c0
c1 The colors at each end of the segment. These can be either
Imager::Color or Imager::Color::Float objects.
segment type
The type of segment, this controls the way the fill parameter
varies over the segment. 0 for linear, 1 for curved
(unimplemented), 2 for sine, 3 for sphere increasing, 4 for
sphere decreasing.
color type
The way the color varies within the segment, 0 for simple RGB,
1 for hue increasing and 2 for hue decreasing.
Don't forget to use Imager::Fountain instead of building your own.
Really. It even loads GIMP gradient files.
# build the gradient the hard way - linear from black to white,
# then back again
my @simple =
(
[ 0, 0.25, 0.5, 'black', 'white', 0, 0 ],
[ 0.5. 0.75, 1.0, 'white', 'black', 0, 0 ],
);
# across
my $linear = $img->copy;
$linear->filter(type => "fountain",
ftype => 'linear',
repeat => 'sawtooth',
segments => \@simple,
xa => 0,
ya => $linear->getheight / 2,
xb => $linear->getwidth - 1,
yb => $linear->getheight / 2)
or die $linear->errstr;
# around
my $revolution = $img->copy;
$revolution->filter(type => "fountain",
ftype => 'revolution',
segments => \@simple,
xa => $revolution->getwidth / 2,
ya => $revolution->getheight / 2,
xb => $revolution->getwidth / 2,
yb => 0)
or die $revolution->errstr;
# out from the middle
my $radial = $img->copy;
$radial->filter(type => "fountain",
ftype => 'radial',
segments => \@simple,
xa => $im->getwidth / 2,
ya => $im->getheight / 2,
xb => $im->getwidth / 2,
yb => 0)
or die $radial->errstr;
gaussian
performs a Gaussian blur of the image, using "stddev" as the
standard deviation of the curve used to combine pixels, larger
values give bigger blurs. For a definition of Gaussian Blur, see:
http://www.maths.abdn.ac.uk/~igc/tch/mx4002/notes/node99.html
Values of "stddev" around 0.5 provide a barely noticeable blur,
values around 5 provide a very strong blur.
# only slightly blurred
$img->filter(type=>"gaussian", stddev=>0.5)
or die $img->errstr;
# more strongly blurred
$img->filter(type=>"gaussian", stddev=>5)
or die $img->errstr;
gradgen
renders a gradient, with the given colors at the corresponding
points (x,y) in "xo" and "yo". You can specify the way distance is
measured for color blending by setting "dist" to 0 for Euclidean, 1
for Euclidean squared, and 2 for Manhattan distance.
$img->filter(type="gradgen",
xo=>[ 10, 50, 10 ],
yo=>[ 10, 50, 50 ],
colors=>[ qw(red blue green) ]);
hardinvert
inverts the image, black to white, white to black. All color
channels are inverted, excluding the alpha channel if any.
$img->filter(type=>"hardinvert")
or die $img->errstr;
hardinvertall
inverts the image, black to white, white to black. All channels
are inverted, including the alpha channel if any.
$img->filter(type=>"hardinvertall")
or die $img->errstr;
mosaic
produces averaged tiles of the given "size".
$img->filter(type=>"mosaic", size=>5)
or die $img->errstr;
noise
adds noise of the given "amount" to the image. If "subtype" is
zero, the noise is even to each channel, otherwise noise is added
to each channel independently.
# monochrome noise
$img->filter(type=>"noise", amount=>20, subtype=>0)
or die $img->errstr;
# color noise
$img->filter(type=>"noise", amount=>20, subtype=>1)
or die $img->errstr;
radnoise
renders radiant Perlin turbulent noise. The center of the noise is
at ("xo", "yo"), "ascale" controls the angular scale of the noise ,
and "rscale" the radial scale, higher numbers give more detail.
$img->filter(type=>"radnoise", xo=>50, yo=>50,
ascale=>1, rscale=>0.02)
or die $img->errstr;
postlevels
alters the image to have only "levels" distinct level in each
channel.
$img->filter(type=>"postlevels", levels=>10)
or die $img->errstr;
turbnoise
renders Perlin turbulent noise. ("xo", "yo") controls the origin
of the noise, and "scale" the scale of the noise, with lower
numbers giving more detail.
$img->filter(type=>"turbnoise", xo=>10, yo=>10, scale=>10)
or die $img->errstr;
unsharpmask
performs an unsharp mask on the image. This increases the contrast
of edges in the image.
This is the result of subtracting a Gaussian blurred version of the
image from the original. "stddev" controls the "stddev" parameter
of the Gaussian blur. Each output pixel is:
in + scale * (in - blurred)
eg.
$img->filter(type=>"unsharpmask", stddev=>1, scale=>0.5)
or die $img->errstr;
"unsharpmark" has the following parameters:
· "stddev" - this is equivalent to the "Radius" value in the
GIMP's unsharp mask filter. This controls the size of the
contrast increase around edges, larger values will remove fine
detail. You should probably experiment on the types of images
you plan to work with. Default: 2.0.
· "scale" - controls the strength of the edge enhancement,
equivalent to Amount in the GIMP's unsharp mask filter.
Default: 1.0.
watermark
applies "wmark" as a watermark on the image with strength
"pixdiff", with an origin at ("tx", "ty")
$img->filter(type=>"watermark", tx=>10, ty=>50,
wmark=>$wmark_image, pixdiff=>50)
or die $img->errstr;
A demonstration of most of the filters can be found at:
http://www.develop-help.com/imager/filters.html
External Filters
As of Imager 0.48 you can create perl or XS based filters and hook them
into Imager's filter() method:
register_filter()
Registers a filter so it is visible via Imager's filter() method.
Imager->register_filter(type => 'your_filter',
defaults => { parm1 => 'default1' },
callseq => [ qw/image parm1/ ],
callsub => \&your_filter);
$img->filter(type=>'your_filter', parm1 => 'something');
The following parameters are needed:
· "type" - the type value that will be supplied to filter() to
use your filter.
· "defaults" - a hash of defaults for the filter's parameters
· "callseq" - a reference to an array of required parameter
names.
· "callsub" - a code reference called to execute your filter.
The parameters passed to filter() are supplied as a list of
parameter name, value ... which can be assigned to a hash.
The special parameters "image" and "imager" are supplied as the
low level image object from $self and $self itself
respectively.
The function you supply must modify the image in place.
To indicate an error, die with an error message followed by a
newline. "filter()" will store the error message as the
"errstr()" for the invocant and return false to indicate
failure.
sub my_filter {
my %opts = @_;
_is_valid($opts{myparam})
or die "myparam invalid!\n";
# actually do the filtering...
}
See Imager::Filter::Mandelbrot for an example.
Plug-ins
The plug in interface is deprecated. Please use the Imager API, see
Imager::API and "External Filters" for details
It is possible to add filters to the module without recompiling Imager
itself. This is done by using DSOs (Dynamic shared object) available
on most systems. This way you can maintain your own filters and not
have to have it added to Imager, or worse patch every new version of
Imager. Modules can be loaded AND UNLOADED at run time. This means
that you can have a server/daemon thingy that can do something like:
load_plugin("dynfilt/dyntest.so")
or die "unable to load plugin\n";
$img->filter(type=>'lin_stretch', a=>35, b=>200);
unload_plugin("dynfilt/dyntest.so")
or die "unable to load plugin\n";
Someone decides that the filter is not working as it should - dyntest.c
can be modified and recompiled, and then reloaded:
load_plugin("dynfilt/dyntest.so")
or die "unable to load plugin\n";
$img->filter(%hsh);
Note: This has been tested successfully on the following systems:
Linux, Solaris, HPUX, OpenBSD, FreeBSD, TRU64/OSF1, AIX, Win32, OS X.
load_plugin()
This is a function, not a method, exported by default. You should
import this function explicitly for future compatibility if you
need it.
Accepts a single parameter, the name of a shared library file to
load.
Returns true on success. Check Imager->errstr on failure.
unload_plugin()
This is a function, not a method, which is exported by default.
You should import this function explicitly for future compatibility
if you need it.
Accepts a single parameter, the name of a shared library to unload.
This library must have been previously loaded by load_plugin().
Returns true on success. Check Imager->errstr on failure.
A few example plug-ins are included and built (but not installed):
· plugins/dyntest.c - provides the "null" (no action) filter, and
"lin_stretch" filters. "lin_stretch" stretches sample values
between "a" and "b" out to the full sample range.
· plugins/dt2.c - provides the "html_art" filter that writes the
image to the HTML fragment file supplied in "fname" as a HTML
table.
· plugins/flines.c - provides the "flines" filter that dims alternate
lines to emulate an old CRT display. Imager::Filter::Flines
provides the same functionality.
· plugins/mandelbrot.c - provides the "mandelbrot" filter that
renders the Mandelbrot set within the given range of x [-2, 0.5)
and y [-1.25, 1,25). Imager::Filter::Mandelbrot provides a more
flexible Mandelbrot set renderer.
Image Difference
difference()
You can create a new image that is the difference between 2 other
images.
my $diff = $img->difference(other=>$other_img);
For each pixel in $img that is different to the pixel in
$other_img, the pixel from $other_img is given, otherwise the pixel
is transparent black.
This can be used for debugging image differences ("Where are they
different?"), and for optimizing animated GIFs.
Note that $img and $other_img must have the same number of
channels. The width and height of $diff will be the minimum of
each of the width and height of $img and $other_img.
Parameters:
· "other" - the other image object to compare against
· "mindist" - the difference between corresponding samples must
be greater than "mindist" for the pixel to be considered
different. So a value of zero returns all different pixels,
not all pixels. Range: 0 to 255 inclusive. Default: 0.
For large sample images this is scaled down to the range 0 ..
1.
AUTHOR
Arnar M. Hrafnkelsson, Tony Cook <tonyc@cpan.org>.
SEE ALSO
Imager, Imager::Filter::Flines, Imager::Filter::Mandelbrot
REVISION
$Revision$
perl v5.14.3 2012-09-28 Imager::Filters(3)
