Page 548 - Beginning PHP 5.3

Part III: Using PHP in Practice
Creating Images

Now that you understand the some basic image concepts, you can start writing scripts to generate
images. Creating an image in PHP requires four steps:
1. Create a blank image canvas for PHP to work with. This is an area of the Web server ’ s memory
that is set aside for drawing onto.
2. Work through the steps involved in drawing the image that you want. This includes setting up
colors and drawing the shapes and text that you want within your image.
3. Send your finished image to the Web browser or save it to disk.
4. Remove your image from the server ’ s memory.

Creating a New Image

The first thing to do is to create a new blank image canvas to store your new image. To do this you can
use either the imagecreate() function, which creates an 8 - bit palette - based image with a maximum of
256 colors, or use the imagecreatetruecolor() function, which creates a 24 - bit true color image
capable of including up to 16.7 million colors. Both the imagecreate() and imagecreatetruecolor()
functions take two parameters: the width and height of the blank image that you want to create.
For example:
$myImage = imagecreate( 200, 150 );

The blank image that this code creates is 200 pixels wide and 150 pixels high.

Both functions return an image resource (stored in $myImage in the example) that points to the image in
memory. You then pass this image resource to other image functions so that they know which image to
work with.

Allocating Colors

Before you can start drawing on your blank image, you need to decide the color you want to draw with,
then use the imagecolorallocate() function to create the color. This function takes four arguments:
the image resource created by imagecreate() or imagecreatetruecolor() , and the red, green, and
blue components of the color that you ’ d like to create. Each component can have a value between 0
and 255.

For example, the following code creates a green color and stores it in a variable called $myGreen :

$myGreen = imagecolorallocate( $myImage, 51, 153, 51 );

The imagecolorallocate() function returns a color identifier that points to the newly created color.
You can then use this identifier with various drawing functions, as you see in a moment.
What if you ’ ve run out of space to allocate colors? This can happen if a palette - based image created with
imagecreate() already contains 256 colors, and there ’ s no space to allocate a new color. In this case,
imagecolorallocate() returns false .

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