Provided by: libimage-size-perl_3.300-3_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)
WEBP
ICO (Microsoft icon format)
CUR (Microsoft mouse cursor 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 Caching 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 caching 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 played 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 occurred. 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.
SEE ALSO
Image::Magick and Image::Info Perl modules at CPAN. The Graphics::Magick Perl API at
<http://www.graphicsmagick.org/perl.html>.
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 Skytt� (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>. 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>
• AnnoCPAN: Annotated CPAN documentation
<http://annocpan.org/dist/Image-Size>
• CPAN Ratings
<http://cpanratings.perl.org/d/Image-Size>
• Search CPAN
<http://search.cpan.org/dist/Image-Size>
• Project page on GitHub
<http://github.com/rjray/image-size>
REPOSITORY
<https://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>) or the GNU LGPL 2.1
(<http://www.opensource.org/licenses/lgpl-2.1.php>).
AUTHOR
Randy J. Ray "<rjray@blackperl.com>"
perl v5.36.0 2022-10-13 Image::Size(3pm)