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Creating images from scratch with the GD library - PHP

The GD library comes bundled with both PHP 4 and PHP 5. While it is a popular library that has been around for a while, many web developers do not take full advantage of its capabilities. In this five-part series, we will take a close look at what the GB library can do for you, especially in the area of dynamically-generated graphics.

TABLE OF CONTENTS:
  1. A Close Look at the GD Library in PHP
  2. Creating images from scratch with the GD library
  3. An alternative way to create image streams from scratch
  4. Generating dynamic streams from existing GIF images with the GD library
By: Alejandro Gervasio
Rating: starstarstarstarstar / 6
August 15, 2007

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We will start exploring the numerous functions that come bundled with the GD extension by showing how to create a dynamic image from scratch. In this case, this basic task can be performed by using three core GD functions, called "imagecreate()", "imagecolorallocate()" and "imagestring()" respectively.

Concerning the usage of the aforementioned functions, below I coded a simple example, which shows how to utilize these functions:

// example of 'imagecreate()', 'imagecolorallocate()',
'imagestring()' functions
try{
   if(!$image=imagecreate(300,200)){
     throw new Exception('Error creating blank image');
   }
   // create background color for image
   $backColor=imagecolorallocate($image,0,0,255);
   // create text color
   if(!$textColor=imagecolorallocate($image,255,255,255)){
     throw new Exception('Error creating text color');
   }
   // include text string into image stream
   if(!$text=imagestring($image,5,10,90,'This is a sample text
string.',$textColor)){
     throw new Exception('Error creating image text');
   }
   header("Content-type:image/png");
   // display image
   imagepng($image);
   // free up memory
   imagedestroy($image);
}
catch(Exception $e){
   echo $e->getMessage();
   exit();
}

Basically, all the previous examples does is create a 300px X 200px image stream via the "imagecreate()" function, then allocate a white color into the stream by the means of "imagecolorallocate()", and finally include a sample string by using the "imagestring()" function. Two additional functions are used in the proper sequence, that is "imagepng()" and imagedestroy()" to output the image in PNG format to the browser, and free up the memory occupied by the respective image.

The PNG image generated by the previous example is shown below:

As you saw, the above example not only demonstrates how easy it is to create an image from scratch with the GD extension, but how intuitive its main functions are, right?

Also, in a similar fashion, the example can be quickly rewritten, this time using a simple procedural function. This approach is illustrated by the code sample below:

try{
  
// define procedural function
  
function displayTextOnImage($text='This is a sample text
string'){
     if(!$text){
       throw new Exception('Invalid text string'); 
     }
     if(!$image=imagecreate(300,200)){
       throw new Exception('Error creating blank image');
     }
     // create background color for image
     $backColor=imagecolorallocate($image,0,0,255);
     // create text color
     if(!$textColor=imagecolorallocate($image,255,255,255)){
       throw new Exception('Error creating text color');
     }
     // include text string into image stream
     if(!imagestring($image,5,10,90,$text,$textColor)){
       throw new Exception('Error creating image text');
     }
     header("Content-type:image/png");
     // display image
     imagepng($image);
     // free up memory
     imagedestroy($image);
   }
   // display image on the browser
   displayTextOnImage('This text was created with GD.');
}
catch(Exception $e){
   echo $e->getMessage();
   exit();
}

Of course, as you might have guessed, the custom "displayTextOnImage()" function that I defined previously displays a new PNG image on the browser, similar to the one shown below:

All right, now that you hopefully learned how to create an image from scratch by using a few intuitive functions bundled with the GD library, it's a good time to move forward and continue analyzing other useful functions. Thus, in the following section I'll show you how to utilize an alternative GD function to generate basic image streams.

To learn how this brand new function will be used, please click on the link below and keep reading.



 
 
>>> More PHP Articles          >>> More By Alejandro Gervasio
 

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