PHP Tutorial: How to resize an image by using PHP

Writing your our own php script to resize the image dynamically will control both the image size and the file size. Check out the image to the left - which was resized with a php script.

This is how do we do this. You going to make use of the PHP GD library to manipulate the image, and a $_GET parameter to tell PHP which image to re-size. First, you need to open up your main screenshot file and get it’s size and type.

$src_img = imagecreatefrompng('image.png');
$srcsize = getimagesize('image.png');

imagecreatfrompng() creates an image object and stores it in $src_image. If the file is a different type you can replace “png” with “jpeg” or “gif.” getimagesize() stores an array in $srcsize that contains the width of the image ($srcsize[0]), the height of the image ($srcsize[1]), and the filetype of the image ($srcsize[2]). Now you need to create new dimensions for the new image and actually create an image. Let's resize the screenshot to 200 pixels wide - and then adjust the height to maintain the ratio.

$dest_x = 200;
$dest_y = (200 / $srcsize[0]) * $srcsize[1];
$dst_img = imagecreatetruecolor($dest_x, $dest_y);

imagecopyresampled() copies an image ($dst_img) into a new image ($src_img) with a set of given attributes (including our sizes). The “Header” line tells the browser that this is an image - so that it’s not displayed as a bunch of gibberish. Finally, the imagepng() function actually displays the image. Now, you need to clean up and get rid of the image objects. Otherwise, you could end up eatting a lot of memory from the server.

imagedestroy($src_img);
imagedestroy($dst_img);

If you load the script directly, you should simply see the image. PHP creates an image resource and displays it in the browser - as if “resize-image.php” was really “image.png.” Therefore you need to include this new image in an HTML page is use the php script as the src attribute of our <img> tag. Like this.

<img src='resize-image.php' />

The script will execute, create an image, and use that as the src. The last thing you need to do is modify your script so that we can pass it some information. It wouldn’t any good if you had to write a new php script for every image you wanted to resize. Instead, we can use the $_GET array to ---- a variable (the image filename) to our image resizing script. Here’s the entire image resizing script, with the $_GET variable used for the filename.

// Create source image and dimensions
$src_img = imagecreatefrompng($_GET['image']);
$srcsize = getimagesize($_GET['image']);

$dest_x = 200;
$dest_y = (200 / $srcsize[0]) * $srcsize[1];

$dst_img = imagecreatetruecolor($dest_x, $dest_y);

// Resize image
imagecopyresampled($dst_img, $src_img, 0, 0, 0, 0, $dest_x, $dest_y, $srcsize[0], $srcsize[1]);

// Output image
header("content-type: image/png");
imagepng($dst_img);

// Deletes images
imagedestroy($src_img);
imagedestroy($dst_img);

To use this, you need to slightly modify your HTML and add an “image” parameter to the URL of your script. Like so…

<img src='resize-image.php?image=image.png' />

Now you can resize images on the fly the way you want, and when you want.

source:code-sucks.com

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