oracular (3) Imager::Filters.3pm.gz
NAME
Imager::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
autolevels_skew 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
gaussian2 stddevX
stddevY
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 luminance of the image so that the luminance will cover the possible range for the image.
"lsat" and "usat" truncate the range by the specified fraction at the top and bottom of the range
respectively.
# increase contrast, losing little detail
$img->filter(type=>"autolevels")
or die $img->errstr;
The method used here is typically called Histogram Equalization
<http://en.wikipedia.org/wiki/Histogram_equalization>.
"autolevels_skew"
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_skew")
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;
This filter was the original "autolevels" filter, but it's typically useless due to the significant
color skew it can produce.
"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;
"gaussian2"
performs a Gaussian blur of the image, using "stddevX", "stddevY" as the standard deviation of the
curve used to combine pixels on the X and Y axis, respectively. 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 "stddevX" or "stddevY" around 0.5 provide a barely noticeable blur, values around 5 provide
a very strong blur.
# only slightly blurred
$img->filter(type=>"gaussian2", stddevX=>0.5, stddevY=>0.5)
or die $img->errstr;
# blur an image in the Y axis
$img->filter(type=>"gaussian", stddevX=>0, stddevY=>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.
rgb_difference()
You can create a new image that is the difference between 2 other images.
my $diff = $img->rgb_difference(other=>$other_img);
For each pixel in $img that is different to the pixel in $other_img, the arithmetic difference for
the value of the pixel in $img from $other_img per color is given. Transparency is ignored.
This can be used for measuring image differences ("How much are they different?").
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
AUTHOR
Arnar M. Hrafnkelsson, Tony Cook <tonyc@cpan.org>.
SEE ALSO
Imager, Imager::Filter::Flines, Imager::Filter::Mandelbrot
REVISION
$Revision$