The GD library for PHP is available to PHP developers wanting to generate graphics at the server level, or to install imaging applications that require it for manipulation of existing images.

The following image does not exist physically on the server — it’s being calculated and drawn on-the-fly by GD.

To test this yourself, create a PHP file including this:

<?php
// Add values to the graph
$graphValues=array(0,80,23,11,190,245,50,80,111,240,55);

// Define .PNG image
header("Content-type: image/png");
$imgWidth=250;
$imgHeight=250;

// Create image and define colors
$image=imagecreate($imgWidth, $imgHeight);
$colorWhite=imagecolorallocate($image, 235, 255, 255);
$colorGrey=imagecolorallocate($image, 192, 192, 192);
$colorBlue=imagecolorallocate($image, 0, 0, 255);

// Create border around image
imageline($image, 0, 0, 0, 250, $colorGrey);
imageline($image, 0, 0, 250, 0, $colorGrey);
imageline($image, 249, 0, 249, 249, $colorGrey);
imageline($image, 0, 249, 249, 249, $colorGrey);

// Create grid
for ($i=1; $i<11; $i++){
imageline($image, $i*25, 0, $i*25, 250, $colorGrey);
imageline($image, 0, $i*25, 250, $i*25, $colorGrey);
}

// Create line graph
for ($i=0; $i<10; $i++){
imageline($image, $i*25, (250-$graphValues[$i]), ($i+1)*25, (250-$graphValues[$i+1]), $colorBlue);
}

// Output graph and clear image from memory
imagepng($image);
imagedestroy($image);

?>

Then invoke the code on your page with a standard image tag, referencing the PHP file instead of an image file:

<img src="/include/gdtest.php">

For usage information, see the GD documentation at php.net.

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