Ubuntu Manpage: Image::Size - read the dimensions of an image in several popular formats

Provided by: libimage-size-perl_3.232-1_all

NAME

       Image::Size - read the dimensions of an image in several popular formats

SYNOPSIS

           use Image::Size;
           # Get the size of globe.gif
           ($globe_x, $globe_y) = imgsize("globe.gif");
           # Assume X=60 and Y=40 for remaining examples

           use Image::Size 'html_imgsize';
           # Get the size as 'width="X" height="Y"' for HTML generation
           $size = html_imgsize("globe.gif");
           # $size == 'width="60" height="40"'

           use Image::Size 'attr_imgsize';
           # Get the size as a list passable to routines in CGI.pm
           @attrs = attr_imgsize("globe.gif");
           # @attrs == ('-width', 60, '-height', 40)

           use Image::Size;
           # Get the size of an in-memory buffer
           ($buf_x, $buf_y) = imgsize(\$buf);
           # Assuming that $buf was the data, imgsize() needed a
           $ reference to a scalar

DESCRIPTION

       The Image::Size library is based upon the "wwwis" script written by Alex Knowles
       (alex@ed.ac.uk), a tool to examine HTML and add 'width' and 'height' parameters to image
       tags. The sizes are cached internally based on file name, so multiple calls on the same
       file name (such as images used in bulleted lists, for example) do not result in repeated
       computations.

SUBROUTINES/METHODS

Image::Size provides three interfaces for possible import:

imgsize(stream)
Returns a three-item list of the X and Y dimensions (width and height, in that order)
and image type of stream. Errors are noted by undefined (undef) values for the first
two elements, and an error string in the third. The third element can be (and usually
is) ignored, but is useful when sizing data whose type is unknown.

html_imgsize(stream)
Returns the width and height (X and Y) of stream pre-formatted as a single string
'width="X" height="Y"' suitable for addition into generated HTML IMG tags. If the
underlying call to "imgsize" fails, undef is returned. The format returned is dually
suited to both HTML and XHTML.

attr_imgsize(stream)
Returns the width and height of stream as part of a 4-element list useful for routines
that use hash tables for the manipulation of named parameters, such as the Tk or CGI
libraries. A typical return value looks like "("-width", X, "-height", Y)". If the
underlying call to "imgsize" fails, undef is returned.

By default, only "imgsize()" is exported. Any one or combination of the three may be
explicitly imported, or all three may be with the tag :all.

Input Types
The sort of data passed as stream can be one of three forms:

string
If an ordinary scalar (string) is passed, it is assumed to be a file name (either
absolute or relative to the current working directory of the process) and is searched
for and opened (if found) as the source of data. Possible error messages (see
DIAGNOSTICS below) may include file-access problems.

scalar reference
If the passed-in stream is a scalar reference, it is interpreted as pointing to an in-
memory buffer containing the image data.

# Assume that &read_data gets data somewhere (WWW, etc.)
$img = &read_data;
($x, $y, $id) = imgsize(\$img);
# $x and $y are dimensions, $id is the type of the image

Open file handle
The third option is to pass in an open filehandle (such as an object of the "IO::File"
class, for example) that has already been associated with the target image file. The
file pointer will necessarily move, but will be restored to its original position
before subroutine end.

# $fh was passed in, is IO::File reference:
($x, $y, $id) = imgsize($fh);
# Same as calling with filename, but more abstract.

Recognized Formats
Image::Size natively understands and sizes data in the following formats:

GIF
JPG
XBM
XPM
PPM family (PPM/PGM/PBM)
XV thumbnails
PNG
MNG
TIF
BMP
PSD (Adobe PhotoShop)
SWF (ShockWave/Flash)
CWS (FlashMX, compressed SWF, Flash 6)
PCD (Kodak PhotoCD, see notes below)
EMF (Windows Enhanced Metafile Format)

Additionally, if the Image::Magick module is present, the file types supported by it are
also supported by Image::Size. See also "CAVEATS".

When using the "imgsize" interface, there is a third, unused value returned if the
programmer wishes to save and examine it. This value is the identity of the data type,
expressed as a 2-3 letter abbreviation as listed above. This is useful when operating on
open file handles or in-memory data, where the type is as unknown as the size. The two
support routines ignore this third return value, so those wishing to use it must use the
base "imgsize" routine.

Note that when the Image::Magick fallback is used (for all non-natively supported files),
the data type identity comes directly from the 'format' parameter reported by
Image::Magick, so it may not meet the 2-3 letter abbreviation format. For example, a WBMP
file might be reported as 'Wireless Bitmap (level 0) image' in this case.

Information Cacheing and $NO_CACHE
When a filename is passed to any of the sizing routines, the default behavior of the
library is to cache the resulting information. The modification-time of the file is also
recorded, to determine whether the cache should be purged and updated. This was originally
added due to the fact that a number of CGI applications were using this library to
generate attributes for pages that often used the same graphical element many times over.

However, the cacheing can lead to problems when the files are generated dynamically, at a
rate that exceeds the resolution of the modification-time value on the filesystem. Thus,
the optionally-importable control variable $NO_CACHE has been introduced. If this value is
anything that evaluates to a non-false value (be that the value 1, any non-null string,
etc.) then the cacheing is disabled until such time as the program re-enables it by
setting the value to false.

The parameter $NO_CACHE may be imported as with the imgsize routine, and is also imported
when using the import tag ":all". If the programmer chooses not to import it, it is still
accessible by the fully-qualified package name, $Image::Size::NO_CACHE.

Sharing the Cache Between Processes
If you are using Image::Size in a multi-thread or multi-process environment, you may wish
to enable sharing of the cached information between the processes (or threads).
Image::Size does not natively provide any facility for this, as it would add to the list
of dependencies.

To make it possible for users to do this themselves, the %CACHE hash-table that
Image::Size uses internally for storage may be imported in the use statement. The user may
then make use of packages such as IPC::MMA (IPC::MMA) that can "tie" a hash to a shared-
memory segment:

use Image::Size qw(imgsize %CACHE);
use IPC::MMA;

...

tie %CACHE, 'IPC::MM::Hash', $mmHash; # $mmHash via mm_make_hash
# Now, forked processes will share any changes made to the cache

Sizing PhotoCD Images
With version 2.95, support for the Kodak PhotoCD image format is included. However, these
image files are not quite like the others. One file is the source of the image in any of a
range of pre-set resolutions (all with the same aspect ratio). Supporting this here is
tricky, since there is nothing inherent in the file to limit it to a specific resolution.

The library addresses this by using a scale mapping, and requiring the user (you) to
specify which scale is preferred for return. Like the $NO_CACHE setting described earlier,
this is an importable scalar variable that may be used within the application that uses
Image::Size. This parameter is called $PCD_SCALE, and is imported by the same name. It,
too, is also imported when using the tag ":all" or may be referenced as
$Image::Size::PCD_SCALE.

The parameter should be set to one of the following values:

base/16
base/4
base
base4
base16
base64

Note that not all PhotoCD disks will have included the "base64" resolution. The actual
resolutions are not listed here, as they are constant and can be found in any
documentation on the PCD format. The value of $PCD_SCALE is treated in a case-insensitive
manner, so "base" is the same as "Base" or "BaSe". The default scale is set to "base".

Also note that the library makes no effort to read enough of the PCD file to verify that
the requested resolution is available. The point of this library is to read as little as
necessary so as to operate efficiently. Thus, the only real difference to be found is in
whether the orientation of the image is portrait or landscape. That is in fact all that
the library extracts from the image file.

Controlling Behavior with GIF Images
GIF images present a sort of unusual situation when it comes to reading size. Because
GIFs can be a series of sub-images to be isplayed as an animated sequence, what part does
the user want to get the size for?

When dealing with GIF files, the user may control the behavior by setting the global value
$Image::Size::GIF_BEHAVIOR. Like the PCD setting, this may be imported when loading the
library. Three values are recognized by the GIF-handling code:

0 This is the default value. When this value is chosen, the returned dimensions are
those of the "screen". The "screen" is the display area that the GIF declares in the
first data block of the file. No sub-images will be greater than this in size; if they
are, the specification dictates that they be cropped to fit within the box.

This is also the fastest method for sizing the GIF, as it reads the least amount of
data from the image stream.

1 If this value is set, then the size of the first sub-image within the GIF is returned.
For plain (non-animated) GIF files, this would be the same as the screen (though it
doesn't have to be, strictly-speaking).

When the first image descriptor block is read, the code immediately returns, making
this only slightly-less efficient than the previous setting.

2 If this value is chosen, then the code loops through all the sub-images of the
animated GIF, and returns the dimensions of the largest of them.

This option requires that the full GIF image be read, in order to ensure that the
largest is found.

Any value outside this range will produce an error in the GIF code before any image data
is read.

The value of dimensions other than the view-port ("screen") is dubious. However, some
users have asked for that functionality.

Image::Size AND WEBSERVERS

There are a few approaches to getting the most out of Image::Size in a multi-process
webserver environment. The two most common are pre-caching and using shared memory. These
examples are focused on Apache, but should be adaptable to other server approaches as
well.

Pre-Caching Image Data
One approach is to include code in an Apache start-up script that reads the information on
all images ahead of time. A script loaded via "PerlRequire", for example, becomes part of
the server memory before child processes are created. When the children are created, they
come into existence with a pre-primed cache already available.

The shortcoming of this approach is that you have to plan ahead of time for which image
files you need to cache. Also, if the list is long-enough it can slow server start-up
time.

The advantage is that it keeps the information centralized in one place and thus easier to
manage and maintain. It also requires no additional CPAN modules.

Shared Memory Caching
Another approach is to introduce a shared memory segment that the individual processes all
have access to. This can be done with any of a variety of shared memory modules on CPAN.

Probably the easiest way to do this is to use one of the packages that allow the tying of
a hash to a shared memory segment. You can use this in combination with importing the hash
table variable that is used by Image::Size for the cache, or you can refer to it
explicitly by full package name:

use IPC::Shareable;
use Image::Size;

tie %Image::Size::CACHE, 'IPC::Shareable', 'size', { create => 1 };

That example uses IPC::Shareable (see IPC::Shareable) and uses the option to the "tie"
command that tells IPC::Shareable to create the segment. Once the initial server process
starts to create children, they will all share the tied handle to the memory segment.

Another package that provides this capability is IPC::MMA (see IPC::MMA), which provides
shared memory management via the mm library from Ralf Engelschall (details available in
the documentation for IPC::MMA):

use IPC::MMA;
use Image::Size qw(%CACHE);

my $mm = mm_create(65536, '/tmp/test_lockfile');
my $mmHash = mm_make_hash($mm);
tie %CACHE, 'IPC::MM::Hash', $mmHash;

As before, this is done in the start-up phase of the webserver. As the child processes are
created, they inherit the pointer to the existing shared segment.

MORE EXAMPLES

       The attr_imgsize interface is also well-suited to use with the Tk extension:

           $image = $widget->Photo(-file => $img_path, attr_imgsize($img_path));

       Since the "Tk::Image" classes use dashed option names as "CGI" does, no further
       translation is needed.

       This package is also well-suited for use within an Apache web server context.  File sizes
       are cached upon read (with a check against the modified time of the file, in case of
       changes), a useful feature for a mod_perl environment in which a child process endures
       beyond the lifetime of a single request.  Other aspects of the mod_perl environment
       cooperate nicely with this module, such as the ability to use a sub-request to fetch the
       full pathname for a file within the server space. This complements the HTML generation
       capabilities of the CGI module, in which "CGI::img" wants a URL but "attr_imgsize" needs a
       file path:

           # Assume $Q is an object of class CGI, $r is an Apache request object.
           # $imgpath is a URL for something like "/img/redball.gif".
           $r->print($Q->img({ -src => $imgpath,
                               attr_imgsize($r->lookup_uri($imgpath)->filename) }));

       The advantage here, besides not having to hard-code the server document root, is that
       Apache passes the sub-request through the usual request lifecycle, including any stages
       that would re-write the URL or otherwise modify it.

DIAGNOSTICS

       The base routine, "imgsize", returns undef as the first value in its list when an error
       has occured. The third element contains a descriptive error message.

       The other two routines simply return undef in the case of error.

CAVEATS

       Caching of size data can only be done on inputs that are file names. Open file handles and
       scalar references cannot be reliably transformed into a unique key for the table of cache
       data. Buffers could be cached using the MD5 module, and perhaps in the future I will make
       that an option. I do not, however, wish to lengthen the dependency list by another item at
       this time.

       As Image::Magick operates on file names, not handles, the use of it is restricted to cases
       where the input to "imgsize" is provided as file name.

CONTRIBUTORS

       Perl module interface by Randy J. Ray (rjray@blackperl.com), original image-sizing code by
       Alex Knowles (alex@ed.ac.uk) and Andrew Tong (werdna@ugcs.caltech.edu), used with their
       joint permission.

       Some bug fixes submitted by Bernd Leibing (bernd.leibing@rz.uni-ulm.de).  PPM/PGM/PBM
       sizing code contributed by Carsten Dominik (dominik@strw.LeidenUniv.nl). Tom Metro
       (tmetro@vl.com) re-wrote the JPG and PNG code, and also provided a PNG image for the test
       suite. Dan Klein (dvk@lonewolf.com) contributed a re-write of the GIF code.  Cloyce
       Spradling (cloyce@headgear.org) contributed TIFF sizing code and test images. Aldo Calpini
       (a.calpini@romagiubileo.it) suggested support of BMP images (which I really should have
       already thought of :-) and provided code to work with. A patch to allow html_imgsize to
       produce valid output for XHTML, as well as some documentation fixes was provided by
       Charles Levert (charles@comm.polymtl.ca). The ShockWave/Flash support was provided by
       Dmitry Dorofeev (dima@yasp.com). Though I neglected to take note of who supplied the PSD
       (PhotoShop) code, a bug was identified by Alex Weslowski <aweslowski@rpinteractive.com>,
       who also provided a test image. PCD support was adapted from a script made available by
       Phil Greenspun, as guided to my attention by Matt Mueller mueller@wetafx.co.nz. A thorough
       read of the documentation and source by Philip Newton Philip.Newton@datenrevision.de found
       several typos and a small buglet. Ville Skyttae (ville.skytta@iki.fi) provided the MNG and
       the Image::Magick fallback code. Craig MacKenna (mackenna@animalhead.com) suggested making
       the cache available so that it could be used with shared memory, and helped test my change
       before release.

BUGS

       Please report any bugs or feature requests to "bug-image-size at rt.cpan.org", or through
       the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Image-Size
       <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Image-Size>. I will be notified, and then
       you'll automatically be notified of progress on your bug as I make changes.

SUPPORT

       •   RT: CPAN's request tracker

           http://rt.cpan.org/NoAuth/Bugs.html?Dist=Image-Size
           <http://rt.cpan.org/NoAuth/Bugs.html?Dist=Image-Size>

       •   AnnoCPAN: Annotated CPAN documentation

           http://annocpan.org/dist/Image-Size <http://annocpan.org/dist/Image-Size>

       •   CPAN Ratings

           http://cpanratings.perl.org/d/Image-Size <http://cpanratings.perl.org/d/Image-Size>

       •   Search CPAN

           http://search.cpan.org/dist/Image-Size <http://search.cpan.org/dist/Image-Size>

       •   Project page on GitHub

           http://github.com/rjray/image-size <http://github.com/rjray/image-size>

LICENSE AND COPYRIGHT

       This file and the code within are copyright (c) 1996-2009 by Randy J. Ray.

       Copying and distribution are permitted under the terms of the Artistic License 2.0
       (http://www.opensource.org/licenses/artistic-license-2.0.php
       <http://www.opensource.org/licenses/artistic-license-2.0.php>) or the GNU LGPL 2.1
       (http://www.opensource.org/licenses/lgpl-2.1.php
       <http://www.opensource.org/licenses/lgpl-2.1.php>).

AUTHOR

       Randy J. Ray "<rjray@blackperl.com>"