PerlMagick, Perl API

PerlMagick is an object-oriented Perl interface to ImageMagick. Use the module to read, manipulate, or write an image or image sequence from within a Perl script. This makes it very suitable for Web CGI scripts. You must have ImageMagick 6.5.5 or above and Perl version 5.005_02 or greater installed on your system for PerlMagick to build properly.

There are a number of useful scripts available to show you the value of PerlMagick. You can do Web based image manipulation and conversion with MagickStudio, or use L-systems to create images of plants using mathematical constructs, and finally navigate through collections of thumbnail images and select the image to view with the WebMagick Image Navigator.

You can try PerlMagick from your Web browser at the ImageMagick Studio. Or, you can see examples of select PerlMagick functions.

Installation

UNIX

Is PerlMagick available from your system RPM repository? For example, on our CentOS system, we install PerlMagick thusly:

yum install ImageMagick-perl

If not, you must install PerlMagick from the ImageMagick source distribution. Download the latest source release.

Unpack the distribution with this command:

tar xvzf ImageMagick.tar.gz

Next configure and compile ImageMagick:

cd ImageMagick-7.1.2-34
./configure -with-perl
make

If ImageMagick / PerlMagick configured and compiled without complaint, you are ready to install it on your system. Administrator privileges are required to install. To install, type

sudo make install

You may need to configure the dynamic linker run-time bindings:

sudo ldconfig /usr/local/lib

Finally, verify the PerlMagick install worked properly, type

perl -MImage::Magick -le 'print Image::Magick->QuantumDepth'

Congratulations, you have a working ImageMagick distribution and you are ready to use PerlMagick to convert, compose, or edit your images.

Windows XP / Windows 2000

ImageMagick must already be installed on your system. Also, the ImageMagick source distribution for Windows 2000 is required. You must also have the nmake from the Visual C++ or J++ development environment. Copy \bin\IMagick.dll and \bin\X11.dll to a directory in your dynamic load path such as c:\perl\site\5.00502.

Next, type

cd PerlMagick
perl Makefile.nt
nmake
nmake install

Running the Regression Tests

To verify a correct installation, type

make test

Use nmake test under Windows. There are a few demonstration scripts available to exercise many of the functions PerlMagick can perform.

Use the prove utility to execute a test from the build folder:

prove --blib blib -I `pwd` -bv ./t/read.t

cd demo
make

You are now ready to utilize the PerlMagick methods from within your Perl scripts.

Overview

Any script that wants to use PerlMagick methods must first define the methods within its namespace and instantiate an image object. Do this with:

use Image::Magick;
$image = Image::Magick->new;

PerlMagick is quantum aware. You can request a specific quantum depth when you instantiate an image object:

use Image::Magick::Q16;
$image = Image::Magick::Q16->new;

The new() method takes the same parameters as SetAttribute. For example,

$image = Image::Magick->new(size=>'384x256');

Next you will want to read an image or image sequence, manipulate it, and then display or write it. The input and output methods for PerlMagick are defined in Read or Write an Image. See Set an Image Attribute for methods that affect the way an image is read or written. Refer to Manipulate an Image for a list of methods to transform an image. Get an Image Attribute describes how to retrieve an attribute for an image. Refer to Create an Image Montage for details about tiling your images as thumbnails on a background. Finally, some methods do not neatly fit into any of the categories just mentioned. Review Miscellaneous Methods for a list of these methods.

Once you are finished with a PerlMagick object you should consider destroying it. Each image in an image sequence is stored in virtual memory. This can potentially add up to mebibytes of memory. Upon destroying a PerlMagick object, the memory is returned for use by other Perl methods. The recommended way to destroy an object is with undef:

undef $image;

To delete all the images but retain the Image::Magick object use

@$image = ();

and finally, to delete a single image from a multi-image sequence, use

undef $image->[$x];

The next section illustrates how to use various PerlMagick methods to manipulate an image sequence.

Some of the PerlMagick methods require external programs such as Ghostscript. This may require an explicit path in your PATH environment variable to work properly. For example (in Linux),

$ENV{PATH} = '/../bin:/usr/bin:/usr/local/bin';

Example Script

Here is an example script to get you started:

#!/usr/local/bin/perl
use Image::Magick;
my($image, $x);
$image = Image::Magick->new;
$x = $image->Read('girl.png', 'logo.png', 'rose.png');
warn "$x" if "$x";
$x = $image->Crop(geometry=>'100x100+100+100');
warn "$x" if "$x";
$x = $image->Write('x.png');
warn "$x" if "$x";

The script reads three images, crops them, and writes a single image as a GIF animation sequence. In many cases you may want to access individual images of a sequence. The next example illustrates how this done:

#!/usr/local/bin/perl
use Image::Magick;
my($image, $p, $q);
$image = new Image::Magick;
$image->Read('x1.png');
$image->Read('j*.jpg');
$image->Read('k.miff[1, 5, 3]');
$image->Contrast();
for ($x = 0; $image->[$x]; $x++)
{
  $image->[$x]->Frame('100x200') if $image->[$x]->Get('magick') eq 'GIF';
  undef $image->[$x] if $image->[$x]->Get('columns') < 100;
}
$p = $image->[1];
$p->Draw(stroke=>'red', primitive=>'rectangle', points=>'20,20 100,100');
$q = $p->Montage();
undef $image;
$q->Write('x.miff');

Suppose you want to start out with a 100 by 100 pixel white canvas with a red pixel in the center. Try

$image = Image::Magick->new;
$image->Set(size=>'100x100');
$image->ReadImage('canvas:white');
$image->Set('pixel[49,49]'=>'red');

Here we reduce the intensity of the red component at (1,1) by half:

@pixels = $image->GetPixel(x=>1,y=>1);
$pixels[0]*=0.5;
$image->SetPixel(x=>1,y=>1,color=>\@pixels);

Or suppose you want to convert your color image to grayscale:

$image->Quantize(colorspace=>'gray');

Let's annotate an image with a Taipei TrueType font:

$text = 'Works like magick!';
$image->Annotate(font=>'kai.ttf', pointsize=>40, fill=>'green', text=>$text);

Perhaps you want to extract all the pixel intensities from an image and write them to STDOUT:

@pixels = $image->GetPixels(map=>'I', height=>$height, width=>$width, normalize=>true);
binmode STDOUT;
print pack('B*',join('',@pixels));

Other clever things you can do with a PerlMagick objects include

$i = $#$p+1;      # return the number of images associated with object p
push(@$q, @$p);  # push the images from object p onto object q
@$p = ();        # delete the images but not the object p
$p->Convolve([1, 2, 1, 2, 4, 2, 1, 2, 1]);   # 3x3 Gaussian kernel

Read or Write an Image

Use the methods listed below to either read, write, or display an image or image sequence:

For convenience, methods Write(), Display(), and Animate() can take any parameter that SetAttribute knows about. For example,

$image->Write(filename=>'image.png', compression=>'None');

Use - as the filename to method Read() to read from standard in or to method Write() to write to standard out:

binmode STDOUT;
$image->Write('png:-');

To read an image in the GIF format from a PERL filehandle, use:

$image = Image::Magick->new;
open(IMAGE, 'image.gif');
$image->Read(file=>\*IMAGE);
close(IMAGE);

To write an image in the PNG format to a PERL filehandle, use:

$filename = "image.png";
open(IMAGE, ">$filename");
$image->Write(file=>\*IMAGE, filename=>$filename);
close(IMAGE);

Note, reading from or writing to a Perl filehandle may fail under Windows due to different versions of the C-runtime libraries between ImageMagick and the ActiveState Perl distributions or if one of the DLL's is linked with the /MT option. See Potential Errors Passing CRT Objects Across DLL Boundaries for an explanation.

If %0Nd, %0No, or %0Nx appears in the filename, it is interpreted as a printf format specification and the specification is replaced with the specified decimal, octal, or hexadecimal encoding of the scene number. For example,

image%03d.miff

converts files image000.miff, image001.miff, etc.

You can optionally add Image to any method name. For example, ReadImage() is an alias for method Read().

Manipulate an Image

Once you create an image with, for example, method ReadImage() you may want to operate on it. Below is a list of all the image manipulations methods available to you with PerlMagick. There are examples of select PerlMagick methods. Here is an example call to an image manipulation method:

$image->Crop(geometry=>'100x100+10+20');
$image->[$x]->Frame("100x200");

And here is a list of other image manipulation methods you can call:

Note that the geometry parameter is a shortcut for the width and height parameters (e.g. geometry=>'106x80' is equivalent to width=>106, height=>80).

You can optionally add Image to any method name above. For example, TrimImage() is an alias for method Trim().

Set an Image Attribute

Use method Set() to set an image attribute. For example,

$image->Set(dither=>'True');
$image->[$x]->Set(delay=>3);

Where this example uses 'True' and this document says '{True, False}', you can use the case-insensitive strings 'True' and 'False', or you can use the integers 1 and 0.

When you call Get() on a Boolean attribute, Image::Magick returns 1 or 0, not a string.

And here is a list of all the image attributes you can set:

SetAttribute() is an alias for method Set().

Get an Image Attribute

Use method Get() to get an image attribute. For example,

($a, $b, $c) = $image->Get('colorspace', 'magick', 'adjoin');
$width = $image->[3]->Get('columns');

In addition to all the attributes listed in Set an Image Attribute, you can get these additional attributes:

GetAttribute() is an alias for method Get().

Compare an Image to its Reconstruction

Mathematically and visually annotate the difference between an image and its reconstruction with the Compare() method. The method supports these parameters:

In this example, we compare the ImageMagick logo to a sharpened reconstruction:

use Image::Magick;
$logo = Image::Magick->New();
$logo->Read('logo:');
$sharp = Image::Magick->New();
$sharp->Read('logo:');
$sharp->Sharpen('0x1');
$difference = $logo->Compare(image=>$sharp, metric=>'rmse');
print $difference->Get('error'), "\n";
$difference->Display();

In addition to the reported root mean squared error of around 0.024, a difference image is displayed so you can visually identify the difference between the images.

Create an Image Montage

Use method Montage() to create a composite image by combining several separate images. The images are tiled on the composite image with the name of the image optionally appearing just below the individual tile. For example,

$image->Montage(geometry=>'160x160', tile=>'2x2', texture=>'granite:');

And here is a list of Montage() parameters you can set:

MontageImage() is an alias for method Montage().

Working with Blobs

A blob contains data that directly represent a particular image format in memory instead of on disk. PerlMagick supports blobs in any of these image formats and provides methods to convert a blob to or from a particular image format.

ImageToBlob() returns the image data in their respective formats. You can then print it, save it to an ODBC database, write it to a file, or pipe it to a display program:

@blobs = $image->ImageToBlob();
open(DISPLAY, "| display -") || die;
binmode DISPLAY;
print DISPLAY $blobs[0];
close DISPLAY;

Method BlobToImage() returns an image or image sequence converted from the supplied blob:

@blob = $db->GetImage();
$image = Image::Magick->new(magick=>'jpg');
$image->BlobToImage(@blob);

Direct-access to Image Pixels

Use these methods to obtain direct access to the image pixels:

Miscellaneous Methods

The Append() method appends a set of images. For example,

$p = $image->Append(stack=>{true,false});

appends all the images associated with object $image. By default, images are stacked left-to-right. Set stack to True to stack them top-to-bottom.

The Clone() method copies a set of images. For example,

$q = $p->Clone();

copies all the images from object $p to $q.

Coalesce() composites a set of images while respecting any page offsets and disposal methods.

$q = $p->Coalesce();

Method Mogrify() is a single entry point for the image manipulation methods. For example, these calls are equivalent:

$image->Crop('340x256+0+0');
$image->Mogrify('crop', '340x256+0+0');

Ping() is a convenience method that returns information about an image without having to read the image into memory:

($width, $height, $size, $format) = $image->Ping('logo.png');

Handling Exceptions

All PerlMagick methods return an undefined string context upon success. If any problems occur, the error is returned as a string with an embedded numeric status code. A status code less than 400 is a warning. A numeric code greater or equal to 400 is an error and indicates the operation failed completely.

Methods which return a number (e.g. Read(), Write()):

$x = $image->Read(...);
warn "$x" if "$x";      # print the error message
$x =~ /(\d+)/;
print $1;               # print the error number
print 0+$x;             # print the number of images read

Review the complete list of error and warning codes.

Constants

PerlMagick includes these constants:

BlobError
BlobWarning
CacheError
CacheWarning
CoderError
CoderWarning
ConfigureError
ConfigureWarning
CorruptImageError
CorruptImageWarning
DelegateError
DelegateWarning
DrawError
DrawWarning
ErrorException
FatalErrorException
FileOpenError
FileOpenWarning
ImageError
ImageWarning
MissingDelegateError
MissingDelegateWarning
ModuleError
ModuleWarning
Opaque
OptionError
OptionWarning
QuantumDepth
QuantumRange
RegistryError
RegistryWarning
ResourceLimitError
ResourceLimitWarning
StreamError
StreamWarning
Success
Transparent
TypeError
TypeWarning
WarningException
XServerError
XServerWarning

You can access them like this:

Image::Magick->QuantumDepth