PHP is a very versatile programming language with many available libraries. A popular one, the GD Library, enables you to manipulate images. This post will take you through the process of manipulating images using the PHP GD library.

To begin any manipulation, one must access an image resource. Here are four functions to accomplish this:

• imagecreate( int $width, int $height ) – creates a blank image resource of the specified size.
• imagecreatefromgif( string $filename ) – creates an image resource from the specified GIF format file.
• imagecreatefromjpeg( string $filename ) – creates an image resource from the specified JPEG format file.
• imagecreatefrompng( string $filename ) – creates an image resource from the specified PNG format file.

All of these functions return ‘resources’, which are used in the GD Library as parameters.

Let us start off with an image called sunburst.jpg. To obtain the resource, use the following snippet:

<?php
	$img = imagecreatefromjpeg( 'sunburst.jpg' );
?>

We shall now proceed on to two more functions, imagesx( resource $image ) and imagesy( resource $image ). imagesx returns the image’s width and imagesy returns the image’s height.

sunburst.jpg has the dimensions 549×359, so the following code:

	echo imagesx( $img ), ' ', imagesy( $img );

will print 549 359.

What good would this image be if we can’t save or display it? The following functions output the resource to the browser or file:

• imagegif( resource $image [, string $filename ] )
• imagejpeg( resource $image [, string $filename ] )
• imagegif( resource $image [, string $filename ] )

For example, if we were to use these functions without the optional parameter $filename:

<?php
	$image = imagecreatefromjpeg( 'sunburst.jpg' );
	header( 'Content-type: image/jpeg' );
	imagejpeg( $image );
	imagedestroy( $image );
?>

sunburst.jpg would be displayed in the browser.

On the other hand, using a $filename:

<?php
	$image = imagecreatefromjpeg( 'sunburst.jpg' );
	imagejpeg( $image, 'sunburstcopy.jpg' );
	imagedestroy( $image );
?>

would output the image to sunburstcopy.jpg.

The function imagedestroy( resource $image ) frees up memory. Remember that each pixel of an image takes up one byte in memory; having several large images open can crash a server. As such, it is always good practice to free up this space.

We can now move to more advanced manipulation:

• imagecopy( resource $dst_im, resource $src_im, int $dst_x, int $dst_y, int $src_x, int $src_y, int $src_w, int $src_h ) – copies an image or part of an image to another image.
• imagecopymerge( resource $dst_im, resource $src_im, int $dst_x, int $dst_y, int $src_x, int $src_y, int $src_w, int $src_h, int $pct ) – copies an image or part of an image to another image with transparency.
• imagecopy( resource $dst_im, resource $src_im, int $dst_x, int $dst_y, int $src_x, int $src_y, int $dst_w, int $dst_h, int $src_w, int $src_h ) – copies an image or part of an image to another image with resampling.

Here are some demonstrations of the above functions.

Imagecopy

Code:

<?php
	$src = imagecreatefromjpeg( 'sunburst.jpg' );
	$dst = imagecreatefromjpeg( 'orchid.jpg' );
	imagecopy( $dst, $src, 10, 10, 0, 0, 200, 200 );
	header( 'Content-type: image/jpeg' );
	imagejpeg( $dst );
	imagedestroy( $src );
	imagedestroy( $dst );
?>

This copies a 200px by 200px square from $src with the top-left corner at (0, 0) to $dst at (10, 10).

Product:

Imagecopymerge

Code:

<?php
	$src = imagecreatefromjpeg( 'sunburst.jpg' );
	$dst = imagecreatefromjpeg( 'orchid.jpg' );
	imagecopymerge( $dst, $src, 10, 10, 0, 0, 200, 200, 50 );
	header( 'Content-type: image/jpeg' );
	imagejpeg( $dst );
	imagedestroy( $src );
	imagedestroy( $dst );
?>

This applies the same effects as the previous example, but with 50% opacity.

Product:

Imagecopyresampled

Code:

<?php
	$src = imagecreatefromjpeg( 'sunburst.jpg' );
	$dst = imagecreatefromjpeg( 'orchid.jpg' );
	imagecopyresampled( $dst, $src, 10, 10, 0, 0, 200, 200, 300, 300 );
	header( 'Content-type: image/jpeg' );
	imagejpeg( $dst );
	imagedestroy( $src );
	imagedestroy( $dst );
?>

This code copies a 300px by 300px square from $src with the top-left corner at (0, 0), resampled to 200px by 100px, to $dst at (10, 10).

Product:

Practical applications for these functions:

Imagecopy – cropped thumbnail

Let us create a 100×100 thumbnail of sunburst.jpg, cropped from the center:

<?php
	$src = imagecreatefromjpeg( 'sunburst.jpg' );
	$dst = imagecreate( 100, 100 ); # Create a blank target image

	# Calculate top-left coordinates of the source by getting the
	# center coordinates and then subtracting half the target width
	$src_x = ( imagesx( $src ) / 2 ) - 50;
	$src_y = ( imagesy( $src ) / 2 ) - 50;

	imagecopy( $dst, $src, 0, 0, $src_x, $src_y, 100, 100 );

	header( 'Content-type: image/jpeg' );
	imagejpeg( $dst );
	imagedestroy( $src );
	imagedestroy( $dst );
?>

The product:

Cropped Thumbnail

Imagecopymerge – watermark

What if I have a logo that needs to be embedded onto my image? The following would suffice:

<?php
	$mark = imagecreatefromjpeg( 'logo.jpg' );
	$dst = imagecreatefromjpeg( 'sunburst.jpg' );

	# Calculate top-left coordinates of the destination by getting
	# getting the bottom coordinates (width, height) and subtracting
	# the width and height of the watermark
	$dst_x = imagesx( $dst ) - imagesx( $mark );
	$dst_y = imagesy( $dst ) - imagesy( $mark );

	imagecopymerge( $dst, $mark, $dst_x, $dst_y, 0, 0, imagesx( $mark ), imagesy( $mark), 50 );

	header( 'Content-type: image/jpeg' );
	imagejpeg( $dst );
	imagedestroy( $mark );
	imagedestroy( $dst );
?>

The product:

Imagecopyresampled – resampled thumbnail

This creates a thumbnail of the original image resampled to a maximum dimension of 100px. You may recognize this from Create a Simple Picture Gallery with PHP.

<?php
	$src = imagecreatefromjpeg( 'sunburst.jpg' );

	# Calculate width and height based on larger dimension
	if ( ($oldW = imagesx($src)) < ($oldH = imagesy($src)) ) {
		$newW = $oldW * (100 / $oldH);
		$newH = 100;
	} else {
		$newW = 100;
		$newH = $oldH * (100 / $oldW);
	}

	# Create a blank target image
	$dst = imagecreate( $newW, $newH );

	imagecopyresampled( $dst, $src, 0, 0, 0, 0, $newW, $newH imagesx( $src ), imagesy( $src ) );

	header( 'Content-type: image/jpeg' );
	imagejpeg( $dst );
	imagedestroy( $src );
	imagedestroy( $dst );
?>

The product:

Resampled Thumbnail

Cool, eh? Have fun manipulating images.