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.
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.
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.
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.
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 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>"