Create solid color image in PHP

Not related to teaching, but I needed a little snippet of code earlier this week that would create a PNG image using PHP for another site that I’m working on.  I was working on creating open graph tags for several of the pages and wanted to use solid color swatches.

The GD library made it pretty easy.

<?php
$red = 100;
$blue = 150;
$green = 200; 
$my_img = imagecreate( 1000, 1000 );
$background = imagecolorallocate( $my_img, $red, $green, $blue );
header( "Content-type: image/png" );
imagepng( $my_img );
imagecolordeallocate( $my_img, $background );
imagedestroy( $my_img );
die(); 

The first 3 lines define the red, green and blue values in the range between 0 and 255, inclusive. For the actual site I used mod_rewrite so that the filename matched the color requested. But for a demo, this is close enough.

imagecreate creates an empty image that’s then filled with the defined color.

A content-type header of image/png is sent to the browser so that it knows it’s a PNG image.

The data is then sent, the image is destroyed and the script ends with die.