Author image Kevin Ryde
and 1 contributors


Image::Base::GD -- draw images with GD


 use Image::Base::GD;
 my $image = Image::Base::GD->new (-width => 100,
                                   -height => 100);
 $image->rectangle (0,0, 99,99, 'white');
 $image->xy (20,20, 'black');
 $image->line (50,50, 70,70, '#FF00FF');
 $image->line (50,50, 70,70, '#0000AAAA9999');
 $image->save ('/some/filename.png');


Image::Base::GD is a subclass of Image::Base,



Image::Base::GD extends Image::Base to create or update image files in various formats using the GD module and library (libgd version 2 or higher).

Native GD drawing has many more features but this module is an easy way to point Image::Base style code at a GD and is a good way to get PNG and other formats out of Image::Base code.

Colour Names

Colour names for drawing are

    "#RGB"           hex upper or lower case
    "None"           transparent

See GD::Simple for its color_names() list. Special "None" means transparent. Colours are allocated when first used. GD works in 8-bit components so 3 and 4-digit hex forms are truncated to the high 2 digits, and 1-digit hex "#123" expands to "#112233".

File Formats

GD can read and write

    png      with libpng
    jpeg     with libjpeg
    gif      unless disabled in
    wbmp     wireless app bitmap
    gd       GD's own format, raw
    gd2      GD's own format, compressed

And read-only,

    xpm      with libXpm

PNG, JPEG and XPM are available if libgd is compiled with the respective support libraries. GIF will be unavailable if the Perl GD interface was built with its option to disable GIF.

load() auto-detects the file format and calls the corresponding newFromPng() etc. "gd" file format differs between libgd 1.x and 2.x. libgd 2.x can load the 1.x format, but always writes 2.x so that's what save() here gives. Both "gd" formats are a byte dump mainly intended for temporary files.

WBMP is a bitmap format and is treated by GD as colours black "#000000" for 0 and white "#FFFFFF" for 1. On save any non-black is treated as white 1 too, but not sure that's a documented feature.

Other GD Modules

Some other modules implement a GD-like interface with other output types or features. To the extent they're GD-compatible they should work passed in as a -gd object here.

GD::SVG::Image (see GD::SVG) can be saved with -file_format set to "svg". (Or see Image::Base::SVG to go directly to an SVG module object if that's desired.)

Image::WMF (see Image::WMF) can be saved by setting -file_format to "wmf".

GD::Window (see GD::Window) as of its version 0.02 almost works in passThrough mode, but look for a bug fix post 0.02.


See "FUNCTIONS" in Image::Base for the behaviour common to all Image-Base classes.

$image = Image::Base::GD->new (key=>value,...)

Create and return a new image object. A new image can be started with -width and -height,

    $image = Image::Base::GD->new (-width => 200, -height => 100);

Or an existing file can be read,

    $image = Image::Base::GD->new (-file => '/some/filename.png');

Or a GD::Image object can be given,

    $image = Image::Base::GD->new (-gd => $gdimageobject);
$new_image = $image->new (key=>value,...)

Create and return a copy of $image. The GD within $image is cloned (per $gd->clone()). The optional parameters are applied to the new image as per set().

    # copy image, new compression level
    my $new_image = $image->new (-zlib_compression => 9);
$colour = $image->xy ($x, $y)
$image->xy ($x, $y, $colour)

Get or set an individual pixel.

Currently the $colour return is hex "#RRGGBB", or "None" for a fully transparent pixel. Partly transparent pixels are returned as a colour.

$image->rectangle ($x1,$y1, $x2,$y2, $colour, $fill)

Draw a rectangle with corners at $x1,$y1 and $x2,$y2. If $fill is true then it's filled, otherwise just the outline.

GD library 2.0.36 has a bug when drawing 1-pixel high $y1 == $y2 unfilled rectangles where it adds 3-pixel high sides to the result. Image::Base::GD has a workaround to avoid that. The intention isn't to second guess GD, but this fix is easy to apply and makes the output consistent with other Image::Base modules.

$image->ellipse ($x1,$y1, $x2,$y2, $colour)
$image->ellipse ($x1,$y1, $x2,$y2, $colour, $fill)

Draw an ellipse within the rectangle with top-left corner $x1,$y1 and bottom-right $x2,$y2. Optional $fill true means a filled ellipse.

In the current implementation ellipses with odd length sides (meaning $x2-$x1+1 and $y2-$y1+1 both odd numbers) are drawn with GD. The rest go to Image::Base because GD circa 2.0.36 doesn't seem to draw even widths very well. This different handling for different sizes is a bit inconsistent.

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

Add colours to the GD palette. Colour names are the same as for the drawing functions.

    $image->add_colours ('red', 'green', '#FF00FF');

The drawing functions automatically add a colour if it doesn't already exist so add_colours() in not needed, but it can be used to initialize the palette with particular desired colours.

For a truecolor GD add_colours() does nothing since in that case each pixel has its own RGBA rather than an index into a palette.

$image->load ($filename)

Read the -file, or set -file to $filename and then read. This creates and sets a new underlying -gd because it's not possible to read into an existing GD image object, only a new one.

$image->save ($filename)

Save to -file, or with a $filename argument set -file then save to that. The file format written is taken from the -file_format (see below).


-width (integer, read-only)
-height (integer, read-only)

The size of a GD image cannot be changed once created.

-ncolours (integer, read-only)

The number of colours allocated in the palette, or undef on a truecolor GD (which doesn't have a palette).

This count is similar to the -ncolours of Image::Xpm.

-file_format (string)

The file format as a string like "png" or "jpeg". See "File Formats" above for the choices.

After load() the -file_format is the format read. Setting -file_format can change the format for a subsequent save.

The default is "png", which means a newly created image (not read from a file) is saved as PNG by default.

-quality_percent (0 to 100 or undef)

The image quality when saving to JPEG format. JPEG compresses by reducing colours and resolution. 100 means full quality, no such reductions. undef means the libjpeg default (which is normally 75).

This becomes the $quality parameter to $gd->jpeg().

-zlib_compression (integer 0-9 or -1, default -1)

The amount of data compression to apply when saving. The value is Zlib style 0 for no compression up to 9 for maximum effort. -1 means Zlib's default level (usually 6).

This becomes the $compression_level parameter to $gd->png().


The underlying GD::Image object.


Putting colour "None" into pixels requires GD "alpha blending" turned off. Image::Base::GD turns off blending for GD objects it creates, but currently if you pass in a -gd then you must set the blending yourself if you're going to use None. Is that the best way? The ideal might be to save and restore blending while drawing None, but there's no apparent way to read back the blending out of a GD to later restore. Or maybe turn blending off and leave it off on first drawing any None.


Image::Base, GD, GD::Simple

Image::Base::PNGwriter, Image::Xpm

GD::SVG, GD::Window, Image::WMF



Image-Base-GD is Copyright 2010, 2011, 2012, 2019 Kevin Ryde

Image-Base-GD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version.

Image-Base-GD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with Image-Base-GD. If not, see <>.