Código PHP:
<?php
class ImageManipulator
{
/**
* @var int
*/
protected $width;
/**
* @var int
*/
protected $height;
/**
* @var resource
*/
protected $image;
/**
* Image manipulator constructor
*
* @param string $file OPTIONAL Path to image file or image data as string
* @return void
*/
protected $transparent = true; //the watermark transparency
public function __construct($file = null)
{
if (null !== $file) {
if (is_file($file)) {
$this->setImageFile($file);
} else {
$this->setImageString($file);
}
}
}
/**
* Set image resource from file
*
* @param string $file Path to image file
* @return ImageManipulator for a fluent interface
* @throws InvalidArgumentException
*/
public function setImageFile($file)
{
if (!(is_readable($file) && is_file($file))) {
throw new InvalidArgumentException("Image file $file is not readable");
}
if (is_resource($this->image)) {
imagedestroy($this->image);
}
list ($this->width, $this->height, $type) = getimagesize($file);
switch ($type) {
case IMAGETYPE_GIF :
$this->image = imagecreatefromgif($file);
break;
case IMAGETYPE_JPEG :
$this->image = imagecreatefromjpeg($file);
break;
case IMAGETYPE_PNG :
$this->image = imagecreatefrompng($file);
break;
default :
throw new InvalidArgumentException("Image type $type not supported");
}
return $this;
}
/**
* Set image resource from string data
*
* @param string $data
* @return ImageManipulator for a fluent interface
* @throws RuntimeException
*/
public function setImageString($data)
{
if (is_resource($this->image)) {
imagedestroy($this->image);
}
if (!$this->image = imagecreatefromstring($data)) {
throw new RuntimeException('Cannot create image from data string');
}
$this->width = imagesx($this->image);
$this->height = imagesy($this->image);
return $this;
}
/**
* Resamples the current image
*
* @param int $width New width
* @param int $height New height
* @param bool $constrainProportions Constrain current image proportions when resizing
* @return ImageManipulator for a fluent interface
* @throws RuntimeException
*/
public function resample($width, $height, $constrainProportions = true)
{
if (!is_resource($this->image)) {
throw new RuntimeException('No image set');
}
if ($constrainProportions) {
if ($this->height >= $this->width) {
$width = round($height / $this->height * $this->width);
} else {
$height = round($width / $this->width * $this->height);
}
}
$temp = imagecreatetruecolor($width, $height);
imagecopyresampled($temp, $this->image, 0, 0, 0, 0, $width, $height, $this->width, $this->height);
return $this->_replace($temp);
}
/**
* Enlarge canvas
*
* @param int $width Canvas width
* @param int $height Canvas height
* @param array $rgb RGB colour values
* @param int $xpos X-Position of image in new canvas, null for centre
* @param int $ypos Y-Position of image in new canvas, null for centre
* @return ImageManipulator for a fluent interface
* @throws RuntimeException
*/
public function enlargeCanvas($width, $height, array $rgb = array(), $xpos = null, $ypos = null)
{
if (!is_resource($this->image)) {
throw new RuntimeException('No image set');
}
$width = max($width, $this->width);
$height = max($height, $this->height);
$temp = imagecreatetruecolor($width, $height);
if (count($rgb) == 3) {
$bg = imagecolorallocate($temp, $rgb[0], $rgb[1], $rgb[2]);
imagefill($temp, 0, 0, $bg);
}
if (null === $xpos) {
$xpos = round(($width - $this->width) / 2);
}
if (null === $ypos) {
$ypos = round(($height - $this->height) / 2);
}
imagecopy($temp, $this->image, (int) $xpos, (int) $ypos, 0, 0, $this->width, $this->height);
return $this->_replace($temp);
}
/**
* Crop image
*
* @param int|array $x1 Top left x-coordinate of crop box or array of coordinates
* @param int $y1 Top left y-coordinate of crop box
* @param int $x2 Bottom right x-coordinate of crop box
* @param int $y2 Bottom right y-coordinate of crop box
* @return ImageManipulator for a fluent interface
* @throws RuntimeException
*/
public function crop($x1, $y1 = 0, $x2 = 0, $y2 = 0)
{
if (!is_resource($this->image)) {
throw new RuntimeException('No image set');
}
if (is_array($x1) && 4 == count($x1)) {
list($x1, $y1, $x2, $y2) = $x1;
}
$x1 = max($x1, 0);
$y1 = max($y1, 0);
$x2 = min($x2, $this->width);
$y2 = min($y2, $this->height);
$width = $x2 - $x1;
$height = $y2 - $y1;
$temp = imagecreatetruecolor($width, $height);
imagecopy($temp, $this->image, 0, 0, $x1, $y1, $width, $height);
return $this->_replace($temp);
}
/**
* Replace current image resource with a new one
*
* @param resource $res New image resource
* @return ImageManipulator for a fluent interface
* @throws UnexpectedValueException
*/
protected function _replace($res)
{
if (!is_resource($res)) {
throw new UnexpectedValueException('Invalid resource');
}
if (is_resource($this->image)) {
imagedestroy($this->image);
}
$this->image = $res;
$this->width = imagesx($res);
$this->height = imagesy($res);
return $this;
}
/**
* Save current image to file
*
* @param string $fileName
* @return void
* @throws RuntimeException
*/
public function save($fileName, $type = IMAGETYPE_JPEG)
{
$dir = dirname($fileName);
if (!is_dir($dir)) {
if (!mkdir($dir, 0755, true)) {
throw new RuntimeException('Error creating directory ' . $dir);
}
}
try {
switch ($type) {
case IMAGETYPE_GIF :
if (!imagegif($this->image, $fileName)) {
throw new RuntimeException;
}
break;
case IMAGETYPE_PNG :
if (!imagepng($this->image, $fileName)) {
throw new RuntimeException;
}
break;
case IMAGETYPE_JPEG :
default :
if (!imagejpeg($this->image, $fileName, 95)) {
throw new RuntimeException;
}
}
} catch (Exception $ex) {
throw new RuntimeException('Error saving image file to ' . $fileName);
}
}
/**
* Returns the GD image resource
*
* @return resource
*/
public function getResource()
{
return $this->image;
}
/**
* Get current image resource width
*
* @return int
*/
public function getWidth()
{
return $this->width;
}
/**
* Get current image height
*
* @return int
*/
public function getHeight()
{
return $this->height;
}
} Código PHP:
<?php
// Create a 55x30 image
$im = imagecreatetruecolor(55, 30);
$red = imagecolorallocate($im, 255, 0, 0);
$black = imagecolorallocate($im, 0, 0, 0);
// Make the background transparent
imagecolortransparent($im, $black);
// Draw a red rectangle
imagefilledrectangle($im, 4, 4, 50, 25, $red);
// Save the image
imagepng($im, './imagecolortransparent.png');
imagedestroy($im);
?> 
Respuesta: imagecolortransparent 
