The first and most important step is to make sure that your PHP installations has the GD library enabled. The easiest way to find out if this has been enabled or not is to create a one line PHP program that has only one instruction, phpinfo()

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<?php phpinfo(); ?>

Store this basic program as phpinfo.php in the document root. Then point the browser to

http://localhost/phpinfo.php

If the steps above was followed the browser should now show a lot of information about the PHP installation. In order to find out if the GD have been installed and enabled look for the GD section in the output. The figure below shows a typical output of this section

Figure 3.2. phphinfo() GD-Information

There are three important points to notice here.

In order to remove any remaining doubts that the installation works as intended the following PHP script that only uses the GD library primitives should be run. This allows troubleshooting the installation without involving the additional complexity of JpGraph to make sure that the basics are in place.

Store the script in Example 3.1 your document root as "checkgd.php"

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<?php // content="text/plain; charset=utf-8"
$im = @imagecreate (200, 100) or die ( "cannot create a new gd image.");
$background_color = imagecolorallocate ($im, 240, 240, 240);
$border_color = imagecolorallocate ($im, 50, 50, 50);
$text_color = imagecolorallocate ($im, 233, 14, 91);
 
imagerectangle($im,0,0,199,99,$border_color);
imagestring ($im, 5, 10, 40, "a simple text string", $text_color );
header ("content-type: image/png");
imagepng ($im);
?>

Figure 3.3. Verifying the GD installations (checkgd.php)

Now point the browser to this file and fetch the script. This should show an image in the browser with the text "a simple text string" similar to what is shown in Figure 3.3

In order to be really sure that the GD 2.x version of the GD library is installed (as opposed to just GD 1.x) we need to use a slightly more advanced script that makes use of some features available in GD 2.x but not in GD 1.x. The largest difference is the support for TrueColor images in GD 2.x so we create a script that makes use of a truecolor canvas..

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<?php // content="text/plain; charset=utf-8"
$im =  imagecreatetruecolor ( 300, 200);
$black = imagecolorallocate ($im,  0, 0, 0);
$lightgray = imagecolorallocate ($im,  230, 230, 230);
$darkgreen = imagecolorallocate ($im,  80, 140, 80);
$white = imagecolorallocate ($im,  255, 255, 255);
 
imagefilledrectangle ($im,0,0,299,199 ,$lightgray);
imagerectangle ($im,0,0,299,199,$black);
imagefilledellipse ($im,150,100,210,110,$white);
imagefilledellipse ($im,150,100,200,100,$darkgreen);
header ("Content-type: image/png");
imagepng ($im);
?>

Figure 3.4. Verifying GD2 (checkgd2.php)

In the same way as before store this file on the server and point the browser to it. The result should be the same image as is shown in Figure 3.4

In order to use the library it is absolutely necessary that the above two scrips works as described. If this is not the case the php.ini file needs to be checked as described in the next section.

If neither of the two example above worked and the GD section didn't exist in the output from phpinfo() the chances are that the GD library has not been enabled in the php.ini file.

The first problem to solve is therefore to locate the php.ini file in the installation. Depending on the type of server (and OS) this can be in different places. If the system is running on a Unix server the php.ini file is most likely stored in either /etc/php.ini , /etc/php/php.ini , /etc/php5/php.ini or /etc/php5/apache/php.ini

On a windows server there is no standard location since it completely depends on how the installation of the HTTP server and PHP was done. For example if the WAMP server was installed and put in the top directory c:\wamp\ the php.ini file is installed under c:\wamp\bin\apache\apache2.2.11\bin\php.ini

Open php.ini in a editor and locate the line

extension_dir = <some-path-here>

The directory path specified above is the directory where all PHP extension modules are stored. On a Unix system this is typically specified as /usr/lib/php5/extensions now examine that directory and check if an extension called "gd.so" (for Unix) or "gd.dll" (for Windows) exists (and is un-commented). If this extension cannot be found then this extension needs to be installed. For example, many Unix/Linux installation requires that the extra modules in PHP is manually enabled/installed through the appropriate Packet manager as the example below shows.

$/> sudo zypper install php5-gd

This section is only intended to verify if that support exists for TTF fonts. If this does not work or if it is already known that there are no support for TTF fonts then please go directly to Section 3.4

In order to check if basic TTF font support is available create the following script in the document root and name it checkttf.php

Then it is necessary to locate on the system exactly where the TTF fonts are stored and update the defines for the paths and/or the name of the TTF fonts that is know to exist.

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<?php // content="text/plain; charset=utf-8"
// Change this defines to where Your fonts are stored
DEFINE("TTF_DIR","/usr/share/fonts/truetype/");
 
// Change this define to a font file that You know that You have
DEFINE("TTF_FONTFILE","arial.ttf");
 
// Text to display
DEFINE("TTF_TEXT","Hello World!");
 
$im = imagecreatetruecolor (400, 100);
$white = imagecolorallocate ($im, 255, 255, 255);
$black = imagecolorallocate ($im, 0, 0, 0);
$border_color = imagecolorallocate ($im, 50, 50, 50);
 
imagefilledrectangle($im,0,0,399,99,$white);
imagerectangle($im,0,0,399,99,$border_color);
imagettftext ($im, 30, 0, 90, 60, $black, TTF_DIR.TTF_FONTFILE,TTF_TEXT);
 
header ("Content-type: image/png");
imagepng ($im);
?>

Figure 3.5. Verifying TTF with a known font (checkttf.php)

As usual point the browser to this script and fetch the image. If thing works an image identical to what is shown in Figure 3.5 should be visible.

By default the standard GD image library supports the PNG graphic format.

Hence by default only PNG is supported. If JPEG support is needed this might require additional libraries that must be installed and enabled for usage by PHP/GD (in the php.ini file), again please see PHP documentation for specifics. For most practical purposes PNG is a better format since it normally achieves better compression then GIF (typically by a factor of 2 for the types of images generated by JpGraph).

In comparison with JPEG format PNG is also better for the type of images generated by this library.

So, the bottom line is that there should be very good reasons to choose any other image encoding formats than PNG. By default the image format is set to "auto". This means that JpGraph automatically chooses the best available image encoding format using the preferred order "PNG", "GIF" and "JPG".