Imager::Filters
Imager::Filters
Imager::Filters - Entire Image Filtering Operations
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);
Filters are operations that have similar calling interface.
Parameters:
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 Imager::Engines/tranform or Imager::Engines/transform2 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
bilinear
radial
radial_square
revolution
conical
The repeat option controls how the fill is repeated for some
ftypes after it leaves the AB range:
none
sawtooth
triangle
saw_both
tri_both
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:
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:
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
As of Imager 0.48 you can create perl or XS based filters and hook them into Imager's filter() method:
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.
See Imager::Filter::Mandelbrot for an example.
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 the module itself. This is done by using DSOs (Dynamic shared object) available on most systems. This way you can maintain our own filters and not have to get me to add it, or worse patch every new version of the Module. 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 modified and recompiled.
load_plugin("dynfilt/dyntest.so")
or die "unable to load plugin\n";
$img->filter(%hsh);
An example plugin comes with the module - Please send feedback to addi@umich.edu if you test this.
Note: This seems to test successfully on the following systems: Linux, Solaris, HPUX, OpenBSD, FreeBSD, TRU64/OSF1, AIX. If you test this on other systems please let me know.
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.
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.
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.
Arnar M. Hrafnkelsson, Tony Cook <tony@imager.perl.org>.
Imager, Imager::Filter::Flines, Imager::Filter::Mandelbrot
$Revision: 1767 $