Image::Size
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Image::Size(3) User Contributed Perl Documentation Image::Size(3)
NAME
Image::Size - read the dimensions of an image in several popular for-
mats
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.
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 DIAG-
NOSTICS 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 nec-
essarily 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 for-
mats:
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)
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 abbrevia-
tion as listed above. This is useful when operating on open file han-
dles 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 gener-
ated dynamically, at a rate that exceeds the resolution of the modifi-
cation-time value on the filesystem. Thus, the optionally-importable
control variable $NO_CACHE has been introduced. If this value is any-
thing 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 program-
mer 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 envi-
ronment, you may wish to enable sharing of the cached information
between the processes (or threads). Image::Size does not natively pro-
vide any facility for this, as it would add to the list of dependen-
cies.
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 reso-
lutions (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" reso-
lution. The actual resolutions are not listed here, as they are con-
stant 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 read-
ing 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 set-
ting the global value $Image::Size::GIF_BEHAVIOR. Like the PCD set-
ting, 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 immedi-
ately 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 dubi-
ous. 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 life-
time 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 docu-
ment 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 descrip-
tive 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 dependancy 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::Mag-
ick Perl API at <http://www.graphicsmagick.org/perl.html>.
AUTHORS
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.leib-
ing@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) sug-
gested 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 docu-
mentation 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 Skyttä (ville.skytta@iki.fi) provided the
MNG and the Image::Magick fallback code.
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>
COPYRIGHT & LICENSE
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/artis-
tic-license-2.0.php>) or the GNU LGPL 2.1 (<http://www.open-
source.org/licenses/lgpl-2.1.php>).
perl v5.8.8 2009-02-23 Image::Size(3)
