PHP | imagecolortransparent() Function

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The imagecolortransparent() function is an inbuilt function in PHP which is used to define color as transparent. It sets the color of a transparent image. It returns the identifier of the new transparent color. If an image has no transparent color and color not specified then it returns -1.

Syntax:

int imagecolortransparent ( $image, $color )

Parameters: This function accepts two parameters as mentioned above and described below:

$image: It is returned by one of the image creation functions, such as imagecreatetruecolor(). It is used to create size of image.
$color: This parameter is used to set the color identifier created by imagecolorallocate() function.

Return Value: This function returns the identifier of the new transparent color. If the color of an image is not specified and the image has no transparent color then it returns -1.

Below programs illustrate the imagecolortransparent() function in PHP:

Program 1:

<?php 
  
// Create an image of size 500x400 
$image = imagecreatetruecolor(500, 400); 
  
// Allocate green color to image 
$green = imagecolorallocate($image, 0, 153, 0); 
  
// Allocate black color to image 
$black = imagecolorallocate($image, 0, 0, 0); 
   
// Make the background transparent 
imagecolortransparent($image, $black); 
   
// Draw a green filled rectangle  
imagefilledrectangle($image, 50, 50, 450, 300, $green); 
   
// Output the image to the browser 
header('Content-Type: image/png'); 
    
imagepng($image); 
   
imagedestroy($image); 
?> 

output:

Program 2:

<?php 
  
// Create an image of size 500x400 
$image = imagecreatetruecolor(500, 400); 
  
// Allocate green color to image 
$green = imagecolorallocate($image, 0, 153, 0); 
  
// Allocate black color to image 
$black = imagecolorallocate($image, 0, 0, 0); 
   
// Make the background transparent 
imagecolortransparent($image, $black); 
   
// Function to draw the circle 
imageellipse($image, 250, 200, 250, 250, $green); 
   
// Output the image to the browser 
header('Content-Type: image/png'); 
    
imagepng($image); 
   
imagedestroy($image); 
?> 