PHP | imagecolortransparent() Function

Last Updated : 23 Aug, 2019

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:

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<?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:

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<?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); ?>