Provided by: libimage-size-perl_3.300-1_all bug


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


           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
           @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


       The Image::Size library is based upon the "wwwis" script written by Alex Knowles
       (, 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


       Image::Size provides three interfaces for possible import:

           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.

           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.

           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:

           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:

       PPM family (PPM/PGM/PBM)
       XV thumbnails
       PSD (Adobe PhotoShop)
       SWF (ShockWave/Flash)
       CWS (FlashMX, compressed SWF, Flash 6)
       PCD (Kodak PhotoCD, see notes below)
       EMF (Windows Enhanced Metafile Format)
       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

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


       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.


       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

   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

       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.


       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.


       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.


       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.


       Image::Magick and Image::Info Perl modules at CPAN. The Graphics::Magick Perl API at


       Perl module interface by Randy J. Ray (, original image-sizing code by
       Alex Knowles ( and Andrew Tong (, used with their
       joint permission.

       Some bug fixes submitted by Bernd Leibing (  PPM/PGM/PBM
       sizing code contributed by Carsten Dominik ( Tom Metro
       ( re-wrote the JPG and PNG code, and also provided a PNG image for the test
       suite. Dan Klein ( contributed a re-write of the GIF code.  Cloyce
       Spradling ( contributed TIFF sizing code and test images. Aldo Calpini
       ( 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 ( The ShockWave/Flash support was provided by
       Dmitry Dorofeev ( Though I neglected to take note of who supplied the PSD
       (PhotoShop) code, a bug was identified by Alex Weslowski <>,
       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 A thorough
       read of the documentation and source by Philip Newton found
       several typos and a small buglet. Ville SkyttX ( provided the MNG and
       the Image::Magick fallback code. Craig MacKenna ( suggested making
       the cache available so that it could be used with shared memory, and helped test my change
       before release.


       Please report any bugs or feature requests to "bug-image-size at", or through
       the web interface at <>. I will
       be notified, and then you'll automatically be notified of progress on your bug as I make


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       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
       (<>) or the GNU LGPL 2.1


       Randy J. Ray "<>"