Instant image resize using PHP GD library

While working on an e-commerce website, I once faced a situation when my client requests me to change all the product thumbnail resolutions and I had to resize all the product images manually. In fact, I made a PHP script to resize all the images in a specific folder. But there is an even better solution for this which I found in a later stage. I am going to share a source code of it below.

Copy and paste the below code to a specific place in your project folder. E.g. myproject/functions/resize.php

<?php
//checking if paramateres and file exists 
if (isset($_GET["path"]) && $_GET["path"] != "" && file_exists($_GET["path"])) {
	$path = $_GET["path"];

	//getting extension type (jpg, png, etc) 
	$type = explode(".", $path);
	$ext = strtolower($type[sizeof($type) - 1]);
	$ext = (!in_array($ext, array("jpeg", "png", "gif"))) ? "jpeg" : $ext;

	//get image size 
	$size = getimagesize($path);
	$width = $size[0];
	$height = $size[1];

	//get source image 
	$func = "imagecreatefrom" . $ext;
	$source = $func($path);

	//setting default values 
	$new_width = $width;
	$new_height = $height;
	$k_w = 1;
	$k_h = 1;
	$dst_x = 0;
	$dst_y = 0;
	$src_x = 0;
	$src_y = 0;

	//selecting width and height 
	if (!isset($_GET["width"]) && !isset($_GET["height"])) {
		$new_height = $height;
		$new_width = $width;
	} else if (!isset($_GET["width"])) {
		$new_height = $_GET["height"];
		$new_width = ($width * $_GET["height"]) / $height;
	} else if (!isset($_GET["height"])) {
		$new_height = ($height * $_GET["width"]) / $width;
		$new_width = $_GET["width"];
	} else {
		$new_width = $_GET["width"];
		$new_height = $_GET["height"];
	}

	//secelcting_offsets 
	if ($new_width > $width) {
		//by width 
		$dst_x = ($new_width - $width) / 2;
	}

	if ($new_height > $height) {
		//by height 
		$dst_y = ($new_height - $height) / 2;
	}
	if ($new_width < $width || $new_height < $height) {
		$k_w = $new_width / $width;
		$k_h = $new_height / $height;
		if ($new_height > $height) {
			$src_x = ($width - $new_width) / 2;
		} else if ($new_width > $width) {
			$src_y = ($height - $new_height) / 2;
		} else {
			if ($k_h > $k_w) {
				$src_x = round(($width - ($new_width / $k_h)) / 2);
			} else {
				$src_y = round(($height - ($new_height / $k_w)) / 2);
			}
		}
	}
	$output = imagecreatetruecolor($new_width, $new_height);

	//to preserve PNG transparency 
	if ($ext == "png") {

		//saving all full alpha channel information 
		imagesavealpha($output, true);

		//setting completely transparent color 
		$transparent = imagecolorallocatealpha($output, 0, 0, 0, 127);

		//filling created image with transparent color 
		imagefill($output, 0, 0, $transparent);
	}
	imagecopyresampled($output, $source, $dst_x, $dst_y, $src_x, $src_y, $new_width - 2 * $dst_x, $new_height - 2 * $dst_y, $width - 2 * $src_x, $height - 2 * $src_y);

	//free resources 
	ImageDestroy($source);

	//output image 
	header('Content-Type: image/' . $ext);
	$func = "image" . $ext;
	$func($output);

	//free resources 
	ImageDestroy($output);
}

Now in your HTML code, wherever you have written tags, use it the way I have done below example.

$image_path = "myproject/images/product-1.jpg";

<img src="/myproject/resize.php?path=<?php=$image_path;?>&width=205&height=310" />

So basically we are passing the resize.php file as the image source and then giving 3 values as a query string.

1. path – it is the original image path which is obviously a bigger sized image
2. width – the width of the resized thumbnail
3. height – the height of the resized thumbnail

This way it will simply resize the image and render it on front-end. Plus you don’t need to store this resized image anywhere as it will be resized under the server cache and then rendered.

Hope you guys find it helpful.