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Randy J Ray

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.

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)
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 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 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 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.

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.

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.

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.

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

http://www.tardis.ed.ac.uk/~ark/wwwis/ for a description of wwwis and how to obtain it, Image::Magick.

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.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 Skyttä (ville.skytta@iki.fi) provided the MNG and the Image::Magick fallback code.

1 POD Error

The following errors were encountered while parsing the POD:

Around line 583:

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