[FIXED] How can I have a nice radial transparent gradient applied to an image with PHP?

Issue

How can one specify an image and apply a radial transparent gradient where it fades out radially. I do not have Imagemagick installed.

Marginal example:

Solution

Thanks to the function linked by @Baba I was able to alter the script to allow for semi transparent vignette effect.

<?php
class PhotoEffect
{
  private $_photoLocation;
  private $_width;
  private $_height;
  private $_type;

  private $_originalImage;
  private $_afterImage;

  /**
   * Load image URL in constructor
   */
  final public function __construct($photoLocation)
  {
    $this->_photoLocation = $photoLocation;
    if (!$size = @getimagesize($this->_photoLocation)){
      throw new Exception('Image cannot be handled');
    }
    $this->_width = $size[0];
    $this->_height = $size[1];
    $this->_type = $size[2];


    switch ( $this->_type ) {
      case IMAGETYPE_GIF:
        $this->_originalImage = imagecreatefromgif($this->_photoLocation);
      break;
      case IMAGETYPE_JPEG:
        $this->_originalImage = imagecreatefromjpeg($this->_photoLocation);
      break;
      case IMAGETYPE_PNG:
        $this->_originalImage = imagecreatefrompng($this->_photoLocation);
      break;
      default:
        throw new Exception('Unknown image type');
    }
  }

  /**
   * Destroy created images
   */
  final private function __destruct() {
     if (!empty($this->_originalImage))
     {
       imagedestroy($this->_originalImage);
     }

     if (!empty($this->_afterImage))
     {
       imagedestroy($this->_afterImage);
     }
   }

  /**
   * Apply vignette effect
   */
  final public function Vignette($sharp=0.4, $level=1, $alpha=1)
  {
    if (empty($this->_originalImage))
    {
      throw new Exception('No image');
    }

    if (!is_numeric($sharp) || !($sharp>=0 && $sharp<=10))
    {
      throw new Exception('sharp must be between 0 and 10');            
    }

    if (!is_numeric($level) || !($level>=0 && $level<=1))
    {
      throw new Exception('level must be between 0 and 10');            
    }

    if (!is_numeric($alpha) || !($alpha>=0 && $alpha<=10))
    {
      throw new Exception('alpha must be between 0 and 1');         
    }

    $this->_afterImage = imagecreatetruecolor($this->_width, $this->_height);
    imagesavealpha($this->_afterImage, true);
    $trans_colour = imagecolorallocatealpha($this->_afterImage, 0, 0, 0, 127);
    imagefill($this->_afterImage, 0, 0, $trans_colour);


    for($x = 0; $x < $this->_width; ++$x){
      for($y = 0; $y < $this->_height; ++$y){  
        $index = imagecolorat($this->_originalImage, $x, $y);
        $rgb = imagecolorsforindex($this->_originalImage, $index);

        $l = sin(M_PI / $this->_width * $x) * sin(M_PI / $this->_height * $y);
        $l = pow($l, $sharp);

        $l = 1 - $level * (1 - $l);

        $rgb['red'] *= $l;
        $rgb['green'] *= $l;
        $rgb['blue'] *= $l;
        $rgb['alpha'] = 127 - (127 * ($l*$alpha));


        $color = imagecolorallocatealpha($this->_afterImage, $rgb['red'], $rgb['green'], $rgb['blue'], $rgb['alpha']);

        imagesetpixel($this->_afterImage, $x, $y, $color);  
      }
    }

  }


  /**
   * Ouput PNG with correct header
   */
  final public function OutputPng()
  {
    if (empty($this->_afterImage))
    {
      if (empty($this->_originalImage))
      {
        throw new Exception('No image');
      }
      $this->_afterImage = $this->_originalImage;
    }

    header('Content-type: image/png');
    imagepng($this->_afterImage);
  }

  /**
   * Save PNG
   */
  final public function SavePng($filename)
  {
    if (empty($filename)) {
        throw new Exception('Filename is required');
    }

    if (empty($this->_afterImage))
    {
      if (empty($this->_originalImage))
      {
        throw new Exception('No image');
      }
      $this->_afterImage = $this->_originalImage;
    }

    imagepng($this->_afterImage, $filename);
  }

}


/**
 * How to use
 */
$effect = new PhotoEffect('test.jpg');
$effect->Vignette();
$effect->OutputPng();
?>

Working phpfiddle with the only image I could find on their server, so not that big.

Answered By - Hugo Delsing

Answer Checked By - Robin (PHPFixing Admin)