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Manual Reference Pages  -  IMAGE::BASE (3)

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Image::Base - base class for loading, manipulating and saving images.



 # base class only
 package My::Image::Class;
 use base Image::Base;


This is a base class for image. It shouldn’t be used directly. Known inheritors are Image::Xbm and Image::Xpm and in see SEE ALSO below.

    use Image::Xpm ;

    my $i = Image::Xpm->new( -file => test.xpm ) ;
    $i->line( 1, 1, 3, 7, red ) ;
    $i->ellipse( 3, 3, 6, 7, #ff00cc ) ;
    $i->rectangle( 4, 2, 9, 8, blue ) ;

Subclasses like Image::Xpm and Image::Xbm are stand-alone Perl code implementations of the respective formats. They’re good for drawing and manipulating image files with a modest amount of code and dependencies.

Other inheritors like Image::Base::GD are front-ends to big image libraries. They can be handy for pointing generic Image::Base style code at a choice of modules and supported file formats. Some inheritors like Image::Base::X11::Protocol::Drawable even go to a window etc for direct display.

    More Methods

If you want to create your own algorithms to manipulate images in terms of (x,y,colour) then you could extend this class (without changing the file), like this:

    # Filename:
    package Image::Base ; # Switch to this class to build on it.
    sub mytransform {
        my $self  = shift ;
        my $class = ref( $self ) || $self ;

        # Perform your transformation here; might be drawing a line or filling
        # a rectangle or whatever... getting/setting pixels using $self->xy().

    package main ; # Switch back to the default package.

Now if you require after you’ve used Image::Xpm or any other Image::Base inheriting classes then all these classes will inherit your mytransform() method.



    my $bitmap = Image::Xbm->new( -file => bitmap.xbm ) ;
    my $pixmap = $bitmap->new_from_image( Image::Xpm, -cpp => 1 ) ;
    $pixmap->save( pixmap.xpm ) ;

Note that the above will only work if you’ve installed Image::Xbm and Image::Xpm, but will work correctly for any image object that inherits from Image::Base and respects its API.

You can use this method to transform an image to another image of the same type but with some different characteristics, e.g.

    my $p = Image::Xpm->new( -file => test1.xpm ) ;
    my $q = $p->new_from_image( ref $p, -cpp => 2, -file => test2.xpm ) ;
    $q->save ;


    $i->line( $x0, $y0, $x1, $y1, $colour ) ;

Draw a line from point ($x0,$y0) to point ($x1,$y1) in colour $colour.



    $i->ellipse( $x0, $y0, $x1, $y1, $colour ) ;
    $i->ellipse( $x0, $y0, $x1, $y1, $colour, $fill ) ;

Draw an oval enclosed by the rectangle whose top left is ($x0,$y0) and bottom right is ($x1,$y1) using a line colour of $colour. If optional argument $fill is true then the ellipse is filled.

     **         **                         
    *             *                        
     **         **                         


    $i->rectangle( $x0, $y0, $x1, $y1, $colour ) ;
    $i->rectangle( $x0, $y0, $x1, $y1, $colour, $fill ) ;

Draw a rectangle whose top left is ($x0,$y0) and bottom right is ($x1,$y1) using a line colour of $colour. If $fill is true then the rectangle will be filled.

    *             *                        
    *             *                        
    *             *                        


    $i->diamond( $x0, $y0, $x1, $y1, $colour ) ;
    $i->diamond( $x0, $y0, $x1, $y1, $colour, $fill ) ;

Draw a diamond shape within the rectangle top left ($x0,$y0) and bottom right ($x1,$y1) using a $colour. If optional argument $fill is true then the diamond is filled. For example

       ****   ****
    ***           ***
       ****   ****


Virtual - must be overridden.

Recommend that it at least supports -file (filename), -width and -height.


Not implemented. Recommended for inheritors. Should accept a string serialised using serialise() and return an object (reference).


Not implemented. Recommended for inheritors. Should return a string representation (ideally compressed).


    my $width = $i->get( -width ) ;
    my( $hotx, $hoty ) = $i->get( -hotx, -hoty ) ;

Get any of the object’s attributes. Multiple attributes may be requested in a single call.

See xy get/set colours of the image itself.


Virtual - must be overridden.

Set any of the object’s attributes. Multiple attributes may be set in a single call; some attributes are read-only.

See xy get/set colours of the image itself.


Virtual - must be overridden. Expected to provide the following functionality:

    $i->xy( 4, 11, #123454 ) ;    # Set the colour at point 4,11
    my $colour = $i->xy( 9, 17 ) ;  # Get the colour at point 9,17

Get/set colours using x, y coordinates; coordinates start at 0.

When called to set the colour the value returned is class specific; when called to get the colour the value returned is the colour name, e.g. ’blue’ or ’#f0f0f0’, etc, e.g.

    $colour = xy( $x, $y ) ;  # e.g. #123456
    xy( $x, $y, $colour ) ;   # Return value is class specific

We don’t normally pick up the return value when setting the colour.


Virtual - must be overridden. Expected to provide the following functionality:

    $i->load ;
    $i->load( test.xpm ) ;

Load the image from the -file attribute filename. Or if a filename parameter is given then set -file to that name and load it.


Virtual - must be overridden. Expected to provide the following functionality:

    $i->save ;
    $i->save( test.xpm ) ;

Save the image to the -file attribute filename. Or if a filename parameter is given then set -file to that name and save to there.

The save format depends on the Image::Base subclass. Some implement a -file_format attribute if multiple formats can be saved.


Add colours to the image palette, if applicable.

    $i->add_colours( $name, $name, ...)

The drawing functions add colours as necessary, so this is just a way to pre-load the palette.

add_colours() does nothing for images which don’t have a palette or can’t take advantage of pre-loading colour names. The base code in Image::Base is a no-op.


The attributes for new(), get() and set() are up to the subclasses, but the common settings, when available, include
-width (integers)
-height The size of the image. These might be create-only with new() taking a size which is then fixed. If the image can be resized then set() of -width and/or -height does a resize.
-file (string) Set by new() reading a file, or load() or save() if passed a filename, or just by set() ready for a future load() or save().
-file_format (string) The name of the file format loaded or to save as. This is generally an abbreviation like XPM, set by load() or set() and then used by save().
-hotx (integers, or maybe -1 or maybe undef)
-hoty The coordinates of the hotspot position. Images which can be a mouse cursor or similar have a position within the image which is the active pixel for clicking etc. For example XPM and CUR (cursor form of ICO) formats have hotspot positions.
-zlib_compression (integer -1 to 9, or undef) The compression level for images which use Zlib, such as PNG. 0 is no compression, 9 is maximum compression. -1 is the Zlib compiled-in default (usually 6). undef means no setting to use an image library default if it has one, or the Zlib default.

For reference, PNG format doesn’t record the compression level used in the file, so for it -zlib_compression can be set() to control a save(), but generally won’t read back from a load().

-quality_percent (integer 0 to 100, or undef) The quality level for saving lossy image formats such as JPEG. 0 is the worst quality, 100 is the best. Lower quality should mean a smaller file, but fuzzier. undef means no setting which gives some image library default.



Sloping lines are drawn by a basic Bressenham line drawing algorithm with integer-only calculations. It ends up drawing the same set of pixels no matter which way around the two endpoints are passed.

Would there be merit in rounding odd numbers of pixels according to which way around line ends are given? Eg. a line 0,0 to 4,1 might do 2 pixels on y=0 and 3 on y=1, but 4,1 to 0,0 the other way around. Or better to have consistency either way around? For reference, in the X11 drawing model the order of the ends doesn’t matter for wide lines, but for implementation-dependent thin lines it’s only encouraged, not required.


Ellipses are drawn with the midpoint ellipse algorithm. This algorithm chooses between points x,y or x,y-1 according to whether the position x,y-0.5 is inside or outside the ellipse (and similarly x+0.5,y on the vertical parts).

The current ellipse code ends up with 0.5’s in the values, which means floating point, but is still exact since binary fractions like 0.5 are exactly representable. Some rearrangement and factors of 2 could make it all-integer. The discriminator in the calculation may exceed 53-bits of float mantissa at around 160,000 pixels wide or high. That might affect the accuracy of the pixels chosen, but should be no worse than that.


The current code draws a diamond with the Bressenham line algorithm along each side. Just one line is calculated and is then replicated to the four sides, which ensures the result is symmetric. Rounding in the line (when width not a multiple or height, or vice versa) is biased towards making the pointier vertices narrower. That tends to look better, especially when the diamond is small.

    Image Libraries

The subclasses like GD or PNGwriter which are front-ends to other drawing libraries don’t necessarily use these base algorithms, but can be expected to something sensible within the given line endpoints or ellipse bounding box. (Among the image libraries it’s surprising how variable the quality of the ellipse drawing is.)


Image::Xpm, Image::Xbm, Image::Pbm, Image::Base::GD, Image::Base::Imager, Image::Base::Imlib2, Image::Base::Magick, Image::Base::PNGwriter, Image::Base::SVG, Image::Base::SVGout, Image::Base::Text, Image::Base::Multiplex

Image::Base::Gtk2::Gdk::Drawable, Image::Base::Gtk2::Gdk::Image, Image::Base::Gtk2::Gdk::Pixbuf, Image::Base::Gtk2::Gdk::Pixmap, Image::Base::Gtk2::Gdk::Window

Image::Base::Prima::Drawable, Image::Base::Prima::Image

Image::Base::Tk::Canvas, Image::Base::Tk::Photo

Image::Base::Wx::Bitmap, Image::Base::Wx::DC, Image::Base::Wx::Image

Image::Base::X11::Protocol::Drawable, Image::Base::X11::Protocol::Pixmap, Image::Base::X11::Protocol::Window


Mark Summerfield. I can be contacted as <> - please include the word ’imagebase’ in the subject line.


Copyright (c) Mark Summerfield 2000. All Rights Reserved.

Copyright (c) Kevin Ryde 2010, 2011, 2012.

This module may be used/distributed/modified under the LGPL.

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perl v5.20.3 IMAGE::BASE (3) 2012-08-01

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