phpman > perldoc > Image::Size(3pm)

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 AT ed.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 AT blackperl.com)*, original image-sizing code by
    Alex Knowles *(alex AT ed.uk)* and Andrew Tong *(werdna AT ugcs.edu)*, used with their
    joint permission.

    Some bug fixes submitted by Bernd Leibing *(bernd.leibing AT rz.de)*. PPM/PGM/PBM sizing
    code contributed by Carsten Dominik *(dominik AT strw.nl)*. Tom Metro *(tmetro AT vl.com)*
    re-wrote the JPG and PNG code, and also provided a PNG image for the test suite. Dan Klein
    *(dvk AT lonewolf.com)* contributed a re-write of the GIF code. Cloyce Spradling
    *(cloyce AT headgear.org)* contributed TIFF sizing code and test images. Aldo Calpini
    *(a.calpini AT 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 AT comm.ca)*. The ShockWave/Flash support was provided by Dmitry Dorofeev
    *(dima AT yasp.com)*. Though I neglected to take note of who supplied the PSD (PhotoShop) code, a
    bug was identified by Alex Weslowski <aweslowski AT 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 AT wetafx.nz*. A thorough read of the documentation and
    source by Philip Newton *Philip.Newton AT datenrevision.de* found several typos and a small buglet.
    Ville Skytt� *(ville.skytta AT iki.fi)* provided the MNG and the Image::Magick fallback code. Craig
    MacKenna *(mackenna AT 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 AT blackperl.com>"