PHP | imagecolordeallocate() Function

<?php 

// It create the size of image or blank image. 
$image_size = imagecreatetruecolor(500, 300); 

// Set the background color of image using 
// imagecolorallocate() function. 
$bg = imagecolorallocate($image_size, 0, 103, 0); 

// Use imagecolordeallocate() function to
// deallocate the color
$bg = imagecolordeallocate($image_size, $bg);

// Fill background with above selected color. 
imagefill($image_size, 0, 0, $bg); 

// Output image in the browser 
header("Content-type: image/png"); 
imagepng($image_size); 

// free memory 
imagedestroy($image_size); 

?> 

<?php 

// It create the size of image or blank image. 
$image_size = imagecreatetruecolor(500, 300); 

// Set the background color of image. 
$bg = imagecolorallocate($image_size, 0, 103, 0); 

// Use imagecolordeallocate() function to
// deallocate the color
$bg = imagecolordeallocate($image_size, $bg); 

// Fill background with above selected color. 
imagefill($image_size, 0, 0, $bg); 

// Set the colors of image 
$white_color = imagecolorallocate($image_size, 255, 255, 255); 

// Draw a circle 
imagearc($image_size, 200, 150, 200, 200, 0, 360, $white_color); 

// Output image in the browser 
header("Content-type: image/png"); 
imagepng($image_size); 

?>