Imager::Filters - Entire Image Filtering Operations |
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.
filter()
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;
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
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 the Imager::Engines manpage or transform2() in the Imager::Engines manpage function may be useful.
A reference of the filters follows:
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.
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.
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;
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;
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;
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;
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
ftype
s 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 the Imager::Fill manpage.
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 the Imager::Fountain manpage 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;
=item 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;
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) ]);
$img->filter(type=>"hardinvert") or die $img->errstr;
$img->filter(type=>"hardinvertall") or die $img->errstr;
size
.
$img->filter(type=>"mosaic", size=>5) or die $img->errstr;
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;
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;
levels
distinct level in each
channel.
$img->filter(type=>"postlevels", levels=>10) or die $img->errstr;
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;
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.
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:
register_filter()
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 the Imager::Filter::Mandelbrot manpage for an example.
The plug in interface is deprecated. Please use the Imager API, see the Imager::API manpage 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()
Accepts a single parameter, the name of a shared library file to load.
Returns true on success. Check Imager->errstr on failure.
unload_plugin()
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):
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.
the Imager::Filter::Flines manpage 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). the Imager::Filter::Mandelbrot manpage provides a more flexible
Mandelbrot set renderer.
difference()
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 <tonyc@cpan.org>.
Imager, Imager::Filter::Flines, Imager::Filter::Mandelbrot
$Revision$
Imager::Filters - Entire Image Filtering Operations |