The PHP class is meant to resize images keeping the aspect ratio using GD library . The class can handle
jpg , jpeg , gif and png . Its simple to use , you just need to specify the image path and dimensions .

Usage :

include("resize-class.php");
$resizeObj = new resize('sample.jpg');
$resizeObj -> resizeImage(200, 200, 'landscape');
$resizeObj -> saveImage('sample-resized.jpg', 100);

Class File – resize-class.php

class resize
 {
 private $image;
 private $width;
 private $height;
 private $imageResized;

 function __construct($fileName)
 {
 $this->image = $this->openImage($fileName);
 $this->width  = imagesx($this->image);
 $this->height = imagesy($this->image);
 }

private function openImage($file)
 {
 $extension = strtolower(strrchr($file, '.'));
 switch($extension)
 {
 case '.jpg':
 case '.jpeg':
 $img = @imagecreatefromjpeg($file);
 break;
 case '.gif':
 $img = @imagecreatefromgif($file);
 break;
 case '.png':
 $img = @imagecreatefrompng($file);
 break;
 default:
 $img = false;
 break;
 }
 return $img;
 }

public function resizeImage($newWidth, $newHeight, $option="auto")
 {
 $optionArray = $this->getDimensions($newWidth, $newHeight, $option);
 $optimalWidth  = $optionArray['optimalWidth'];
 $optimalHeight = $optionArray['optimalHeight'];

 $this->imageResized = imagecreatetruecolor($optimalWidth, $optimalHeight);
 imagecopyresampled($this->imageResized, $this->image, 0, 0, 0, 0, $optimalWidth, $optimalHeight, $this->width, $this->height);

 if ($option == 'crop') {
 $this->crop($optimalWidth, $optimalHeight, $newWidth, $newHeight);
 }
 }

 private function getDimensions($newWidth, $newHeight, $option)
 {
 switch ($option)
 {
 case 'exact':
 $optimalWidth = $newWidth;
 $optimalHeight= $newHeight;
 break;
 case 'portrait':
 $optimalWidth = $this->getSizeByFixedHeight($newHeight);
 $optimalHeight= $newHeight;
 break;
 case 'landscape':
 $optimalWidth = $newWidth;
 $optimalHeight= $this->getSizeByFixedWidth($newWidth);
 break;
 case 'auto':
 $optionArray = $this->getSizeByAuto($newWidth, $newHeight);
 $optimalWidth = $optionArray['optimalWidth'];
 $optimalHeight = $optionArray['optimalHeight'];
 break;
 case 'crop':
 $optionArray = $this->getOptimalCrop($newWidth, $newHeight);
 $optimalWidth = $optionArray['optimalWidth'];
 $optimalHeight = $optionArray['optimalHeight'];
 break;
 }
 return array('optimalWidth' => $optimalWidth, 'optimalHeight' => $optimalHeight);
 }

 private function getSizeByFixedHeight($newHeight)
 {
 $ratio = $this->width / $this->height;
 $newWidth = $newHeight * $ratio;
 return $newWidth;
 }

 private function getSizeByFixedWidth($newWidth)
 {
 $ratio = $this->height / $this->width;
 $newHeight = $newWidth * $ratio;
 return $newHeight;
 }

 private function getSizeByAuto($newWidth, $newHeight)
 {
 if ($this->height < $this->width)
 {
 $optimalWidth = $newWidth;
 $optimalHeight= $this->getSizeByFixedWidth($newWidth);
 }
 elseif ($this->height > $this->width)
 {
 $optimalWidth = $this->getSizeByFixedHeight($newHeight);
 $optimalHeight= $newHeight;
 }
 else
 {
 if ($newHeight < $newWidth) {
 $optimalWidth = $newWidth;
 $optimalHeight= $this->getSizeByFixedWidth($newWidth);
 } else if ($newHeight > $newWidth) {
 $optimalWidth = $this->getSizeByFixedHeight($newHeight);
 $optimalHeight= $newHeight;
 } else {
 $optimalWidth = $newWidth;
 $optimalHeight= $newHeight;
 }
 }
 return array('optimalWidth' => $optimalWidth, 'optimalHeight' => $optimalHeight);
 }

 private function getOptimalCrop($newWidth, $newHeight)
 {
 $heightRatio = $this->height / $newHeight;
 $widthRatio  = $this->width /  $newWidth;

 if ($heightRatio < $widthRatio) {
 $optimalRatio = $heightRatio;
 } else {
 $optimalRatio = $widthRatio;
 }
 $optimalHeight = $this->height / $optimalRatio;
 $optimalWidth  = $this->width  / $optimalRatio;
 return array('optimalWidth' => $optimalWidth, 'optimalHeight' => $optimalHeight);
 }

private function crop($optimalWidth, $optimalHeight, $newWidth, $newHeight)
 {
 $cropStartX = ( $optimalWidth / 2) - ( $newWidth /2 );
 $cropStartY = ( $optimalHeight/ 2) - ( $newHeight/2 );
 $crop = $this->imageResized;
 $this->imageResized = imagecreatetruecolor($newWidth , $newHeight);
 imagecopyresampled($this->imageResized, $crop , 0, 0, $cropStartX, $cropStartY, $newWidth, $newHeight , $newWidth, $newHeight);
 }

public function saveImage($savePath, $imageQuality="100")
 {
 $extension = strrchr($savePath, '.');
 $extension = strtolower($extension);

 switch($extension)
 {
 case '.jpg':
 case '.jpeg':
 if (imagetypes() & IMG_JPG) {
 imagejpeg($this->imageResized, $savePath, $imageQuality);
 }
 break;

 case '.gif':
 if (imagetypes() & IMG_GIF) {
 imagegif($this->imageResized, $savePath);
 }
 break;

 case '.png':
 $scaleQuality = round(($imageQuality/100) * 9);
 $invertScaleQuality = 9 - $scaleQuality;
 if (imagetypes() & IMG_PNG) {
 imagepng($this->imageResized, $savePath, $invertScaleQuality);
 }
 break;
 default:
 break;
 }
 imagedestroy($this->imageResized);
 }
}

Download sample code resize-class-example.zip