Simple Image Resize script

gistfile1.php

<?php

/**
 * Convert and resize image JPG, GIF, PNG
 *
 * Example : 
 * function resizeAction ()
 * {
 *   $image = new Image();
 * 
 *   $im = $image->readImage($_GET['filename']);
 *   $new = $image->resize($im, $_GET['width'], $_GET['height'], true);
 *   $image->writeImage($new);
 * 
 *   exit;
 * }
 *
 */
Class Image
{
    const TYPE_JPG = 'jpg';
    const TYPE_GIF = 'gif';
    const TYPE_PNG = 'png';
    const TYPE_TXT = 'txt';

    private $_img;

    public function __construct($img, $type = NULL)
    {
        $res = $this->_readImage($img, $type);
        if($res)
            $this->_img = $res;
        else
            throw new Exception("No image found !");
    }

    private function _filenameToMime ($filename)
    {
        $types = array(
            'jpg' => self::TYPE_JPG,
            'gif' => self::TYPE_GIF,
            'png' => self::TYPE_PNG,
            'txt' => self::TYPE_TXT
        );

        foreach ($types as $extension => $mime)
            if (preg_match('/\.'.$extension.'$/', $filename)) return $mime;
    }

    /**
     * Returns a PHP image resource
     */
    private function _readImage ($filename, $type = NULL)
    {
        if ($type === NULL)
            $type = $this->_filenameToMime($filename);

        switch ($type)
        {
            case self::TYPE_JPG:
                return @imagecreatefromjpeg($filename);
                break;
            case self::TYPE_GIF:
                return @imagecreatefromgif($filename);
                break;

            case self::TYPE_PNG:
                return @imagecreatefrompng($filename);
                break;
            case self::TYPE_TXT:
                return @imagecreatefromstring($filename);
                break;
            default:
                break;
        }
        return false;
    }

    private function _imagealphamask($mask) {

        // Get sizes and set up new picture
        $xSize = imagesx($this->_img);
        $ySize = imagesy($this->_img);
        $newPicture = imagecreatetruecolor( $xSize, $ySize );
        imagesavealpha( $newPicture, true );
        imagefill( $newPicture, 0, 0, imagecolorallocatealpha( $newPicture, 0, 0, 0, 127 ) );

        // Resize mask if necessary
        if( $xSize != imagesx( $mask ) || $ySize != imagesy( $mask ) ) {
            $tempPic = imagecreatetruecolor( $xSize, $ySize );
            imagecopyresampled( $tempPic, $mask, 0, 0, 0, 0, $xSize, $ySize, imagesx( $mask ), imagesy( $mask ) );
            imagedestroy( $mask );
            $mask = $tempPic;
        }

        // Perform pixel-based alpha map application
        for( $x = 0; $x < $xSize; $x++ ) {
            for( $y = 0; $y < $ySize; $y++ ) {
                $alpha = imagecolorsforindex( $mask, imagecolorat( $mask, $x, $y ) );
                $alpha = 127 - floor( $alpha[ 'red' ] / 2 );
                $color = imagecolorsforindex( $this->_img, imagecolorat( $this->_img, $x, $y ) );
                imagesetpixel( $newPicture, $x, $y, imagecolorallocatealpha( $newPicture, $color[ 'red' ], $color[ 'green' ], $color[ 'blue' ], $alpha ) );
            }
        }

        imagedestroy($this->_img);
        $this->_img = $newPicture;
    }

    public function getImage()
    {
        return $this->_img;
    }
    
    public function writeImage ($filename, $forceType = false)
    {
        $type = $this->_filenameToMime($filename);
        $finalType = ($forceType) ? $forceType : $type;
        $filename = ($finalType != $type) ? substr($filename, 0, strlen($filename) - 4).'.'.$finalType : $filename;

        switch ($finalType)
        {
            case self::TYPE_JPG:
                imagejpeg($this->_img, $filename);
                break;
            case self::TYPE_GIF:
                imagegif($this->_img, $filename);
                break;

            case self::TYPE_PNG:
                imagepng($this->_img, $filename);
                break;

            default:
                break;
        }
    }

    public function resize ($width = null, $height = null, $crop = true, $fetch = false, $zoom = false)
    {
        $origW = imagesx($this->_img);
        $origH = imagesy($this->_img);

        $newRatioW = $origW / $width;
        $newRatioH = $origH / $height;

        if($fetch)
        {
            $newImgW = $width;
            $newImgH = $height;
            if($crop)
            {
                if($newRatioW > $newRatioH)
                {
                    $newRatioW = $newRatioH;
                    $newX = 0 - ((($origW / $newRatioW) - $width) / 2);
                    $newY = 0;
                }else{
                    $newRatioH = $newRatioW;
                    $newX = 0;
                    $newY = 0 - ((($origH / $newRatioH) - $height) / 2);
                }
            }else{
                $newX = $newY = 0;
                $newW = $width;
                $newH = $height;
            }
        }else{
            if($crop)
            {
                $newImgH = $height;
                $newImgW = $width;
                if($newRatioW > $newRatioH)
                {
                    if($newRatioH < 1)
                    {
                        if($newRatioW < 1) return true; // No resize needed
                        $newRatioH = 1;
                        $newImgH = $origH;
                    }else
                        if($newRatioW < 1) $newImgW = $origW;
                    $newRatioW = $newRatioH;
                    $newX = 0 - ((($origW / $newRatioW) - $width) / 2);
                    $newY = 0;
                }else{
                    if($newRatioW < 1)
                    {
                        if($newRatioH < 1) return true; // No resize needed
                        $newRatioW = 1;
                        $newImgW = $origW;
                    }else
                        if($newRatioH < 1) $newImgH = $origH;
                    $newRatioH = $newRatioW;
                    $newX = 0;
                    $newY = 0 - ((($origH / $newRatioH) - $height) / 2);
                }
            }else{
                $newX = $newY = 0;
                if($newRatioW < $newRatioH)
                {
                    $newRatioW = $newRatioH;
                    $newImgW = $origW / $newRatioH;
                    $newImgH = $origH / $newRatioH;
                }else{
                    $newRatioH = $newRatioW;
                    $newImgW = $origW / $newRatioW;
                    $newImgH = $origH / $newRatioW;
                }
            }
        }

        // now we know the new image's dimensions
        $newW = $origW / $newRatioW;
        $newH = $origH / $newRatioH;
        $newImg = imagecreatetruecolor($newImgW, $newImgH);
        imagealphablending( $newImg, false );
        imagesavealpha( $newImg, true );
        if($zoom)
        {
            $perc = 1 + ($zoom / 100);
            $newW = $newW * $perc;
            $newH = $newH * $perc;
            $newX -= ($newW - ($newW / $perc)) / 2;
            $newY -= ($newY - ($newY / $perc)) / 2;
        }
        imagecopyresampled($newImg, $this->_img, $newX, $newY, 0, 0, $newW, $newH, $origW, $origH);

        $this->_img = $newImg;
        return true;
    }
}