Page 204 - Open Soource Technologies 304.indd

Unit 12: Images

imagecolordeallocate($line_color); Notes
imagecolordeallocate($text_color);

imagecolordeallocate($background);
imagedestroy($my_img);

?>
The above code creates a 200x80 PNG image with a blue background and yellow text. It can
be called from within your web page simply by referencing the php file. For example, if the
PHP file that contains the above code is called myimage.php, then the HTML code to invoke
it can simply be:

<img src=”myimpage.php” alt=”Image created by a PHP script” width=”200” height=”80”>
Explanation of the Code

• Creating the Image
The first thing the code does is to call the imagecreate() function with the dimensions of
the image, namely its width and height in that order. This function returns a resource
identifier for the image which we save in$my_img. The identifier is needed for all our
operations on the image.

If the function fails for some reason, it will return FALSE. If you want your
code to be robust, you should test for this.

• Using Colours in PHP
Before you can use any sort of colours in your image at all, you will need to allocate the
colour. Colours are represented by three digits, known as the RGB value. The first digit
denotes the red component, the second the green and the third blue, hence RGB, for
Red-Green-Blue. These are the same colour values that you use for your web page as well
as numerous other computer applications.

Colours are allocated using the imagecolorallocate() function. This function will automatically
fill the background of the image with the colour the first time you call it, as well as return
an identifier for that particular colour. Subsequent calls to imagecolorallocate() will simply
create a colour identifier for your colour, without affecting your image background.

As you can see from the above code, my script allocates a blue identifier for the image,
and in so doing, causes imagecolorallocate() to set the background to blue automatically.
It also allocates a colour identifier for yellow and one for a shade of green. The latter two
identifiers will be used later to write text and draw a line.

imagecolorallocate() returns FALSE if the function fails for any reason.

• Writing Text to the Image
To write text to your image, you will need to use the imagestring() function. This function
uses a set of built-in fonts to do the writing. The fonts have various sizes, ranging from 1
to 5, where 1 is the smallest font size and 5 the largest. The size of the font is specified in
the second parameter to the function. The third and fourth parameters to imagestring()
specify the x,y coordinate for the top left hand corner of the text. In the case of the example
above, my text will begin 25 pixels from the top edge of the image, and 30 pixels from the
left.

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