PHP | imagecolortransparent() Function

Last Updated : 11 Jul, 2025

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

<?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: image transparent

Program 2:

php

<?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);
?>