GD Library - Create Transparent Image

PHP Modules Tutorials - Herong's Tutorial Examples

∟GD Module - Manipulating Images and Pictures

∟GD Library - Create Transparent Image

This section provides a tutorial example on how to create an image with transparent background using GD Library functions.

If you want to create an image with a transparent background with the GD Library, here is what you need to remember:

1. Select a color for the background of the image. Make sure this background color is not used to draw any graphical element on the image.

2. Fill the entire image with the background color using imagefilledrectangle().

3. Draw all graphical elements on the image using imageline(), imageRectangle(), etc.

4. Set the background color to be transparent using imagecolortransparent().

5. Save the image in a format that supports transparent background like GIF or PNG.

Below is a PHP script that creates transparent background image in PNG format.

<?php
#  GD-Create-Transparent-Image.php
#- Copyright 2009 (c) HerongYang.com. All Rights Reserved.

$image = imagecreatetruecolor(400,400);

$blue = imagecolorallocate($image, 0, 0, 255);
$green = imagecolorallocate($image, 0, 255, 0);
$red = imagecolorallocate($image, 255, 0, 0);
$black = imagecolorallocate($image, 0, 0, 0);

print("Fill the background...\n");
$bgColor = $black;
imagefilledrectangle($image, 0, 0, 400, 400, $bgColor);

print("Drawing some graphics...\n");
imagefilledrectangle($image, 50, 50, 350, 350, $blue);
imagefilledellipse($image, 200, 200, 200, 200, $green);

print("Open a circle to see the background...\n");
imagefilledellipse($image, 200, 200, 100, 100, $bgColor);

print("Set the background to be transparent...\n");
imagecolortransparent($image, $bgColor);

$file = "GD-Transparent-Graphics.png";
imagepng($image, $file);
print("Image saved:\n");
print("   File: $file\n");
?>

Run the above PHP script example:

php GD-Create-Transparent-Image.php

Fill the background...
Drawing some graphics...
Open a circle to see the background...
Set the background to be transparent...
Image saved:
   File: GD-Transparent-Graphics.png