How Do I Create Thumbnail Images?

[+skyler_sdf]

Building a basic thumbnail is a five stage process:

1. load the source image into a php variable

2. determinate the height and width of the original image

3. create a blank thumbnail image of the correct size

4. copy the original image to the blank thumbnail

5. display the thumbnail using the correct content type.

Let's create a thumbnail from a large version of the SitePoint logo in jpeg format

<?php

//specify source image

$sourceimage='sample_images/sitepoint_logo.jpg';

//Specify thumbnail height and width

$thumbwidht=200;

$thumbheight=100;

//load the source image

$original=imagecreatefromjpeg($sourceimage);

//get the size of the original

$dims=getimagesize($sourceimage);

//create a blank thumbnail (note slightly reduced height)

$thumb=imagecreatetruecolor($thumbwidth, $thumbheight);

//copy a resized version of the original onto the thumbnail

imagecopyresampled($thumb, $original, 0, 0, 0, 0, $thumbwidht, $thumbheight, $dims[0], $dims[1]);

//send the content header

header("Content-type: image/jpeg");

//display the image

imagejpeg($thumb);

?>

imagecreatefromjpeg=load an image from the file system into a PHP variable

The getimagesize function tells us the width and height of the image (more on getimagesize in a moment)

The imagecreatetruecolor function is used to create a blank image(in memory, as a PHP variable) into which the thumbnail image will be placed.

The imagecopyresampled function is the point at which the thumbnail is actually created from the original.It places a resized version of the image into the blank thumbnail image, resambling along the way to ensure that the image is resized smoothly.

We use imagejpeg to output the completed thumbanil.