PHP image similarity code example

/**
* Image similarity comparison
*
* @version $Id: ImageHash.php 4429 2012-04-17 13:20:31Z jax $
* @authorjax.hu
* www.osxue.com
*//Sample_1
*$aHash = ImageHash::hashImageFile('wsz.11.jpg');
*$bHash = ImageHash::hashImageFile('wsz.12.jpg');
*var_dump(ImageHash::isHashSimilar($aHash, $bHash));
*
*//Sample_2
*var_dump(ImageHash::isImageFileSimilar('wsz.11.jpg', 'wsz.12.jpg'));
*
*/
class ImageHash {
 /**Sampling rate 1~10
* @access public
* @staticvar int
**/
 public static $rate = 2;
 /**Similarity allowed value 0~64
* @access public
* @staticvar int
**/
 public static $similarity = 80;
 /**The opening function corresponding to the image type
* @access private
* @staticvar string
**/
 private static $_createFunc = array(
 IMAGETYPE_GIF =>'imageCreateFromGIF',
 IMAGETYPE_JPEG=>'imageCreateFromJPEG',
 IMAGETYPE_PNG =>'imageCreateFromPNG',
 IMAGETYPE_BMP =>'imageCreateFromBMP',
 IMAGETYPE_WBMP=>'imageCreateFromWBMP',
 IMAGETYPE_XBM =>'imageCreateFromXBM',
 );
/**Create an image from a file
* @param string $filePath file address path
* @return resource When the image is successfully opened, the image resource ID is passed, and if it fails, it is false
**/
 public static function createImage($filePath){
 if(!file_exists($filePath)){ return false; }
 /*判断文件类型是否可以开启*/
 $type = exif_imagetype($filePath);
 if(!array_key_exists($type,self::$_createFunc)){ return false; }
 $func = self::$_createFunc[$type];
 if(!function_exists($func)){ return false; }
 return $func($filePath);
 }
/**hash image
* @param resource $src image resource ID
* @return string image hash value, false on failure
**/
 public static function hashImage($src){
 if(!$src){ return false; }
 /*缩小图片尺寸*/
 $delta = 8 * self::$rate;
 $img = imageCreateTrueColor($delta,$delta);
 imageCopyResized($img,$src, 0,0,0,0, $delta,$delta,imagesX($src),imagesY($src));
 /*计算图片灰阶值*/
 $grayArray = array();
 for ($y=0; $y<$delta; $y++){
 for ($x=0; $x<$delta; $x++){
 $rgb = imagecolorat($img,$x,$y);
 $col = imagecolorsforindex($img, $rgb);
 $gray = intval(($col['red']+$col['green']+$col['blue'])/3)& 0xFF;
 $grayArray[] = $gray;
 }
 }
 imagedestroy($img);
 /*计算所有像素的灰阶平均值*/
 $average = array_sum($grayArray)/count($grayArray);
 /*计算 hash 值*/
 $hashStr = '';
 foreach ($grayArray as $gray){
 $hashStr .= ($gray>=$average) ? '1' : '0';
 }
 return $hashStr;
 }
 /**hash image file
* @param string $filePath file address path
* @return string image hash value, false on failure
**/
 public static function hashImageFile($filePath){
 $src = self::createImage($filePath);
 $hashStr = self::hashImage($src);
 imagedestroy($src);
 return $hashStr;
 }
 /**Compare two hash values ​​to see if they are similar
* @param string $aHash The hash value of picture A
* @param string $bHash The hash value of picture B
* @return bool If the pictures are similar, true will be passed, otherwise false
**/
 public static function isHashSimilar($aHash, $bHash){
 $aL = strlen($aHash); $bL = strlen($bHash);
 if ($aL !== $bL){ return false; }
 /*计算容许落差的数量*/
 $allowGap = $aL*(100-self::$similarity)/100;
 /*计算两个 hash 值的汉明距离*/
 $distance = 0;
 for($i=0; $i<$aL; $i++){
 if ($aHash{$i} !== $bHash{$i}){ $distance++; }
 }
 return ($distance<=$allowGap) ? true : false;
 }
/**Compare two image files to see if they are similar
* @param string $aHash The path of image A
* @param string $bHash The path of image B
* @return bool When the images are similar, true is passed, otherwise false
**/
 public static function isImageFileSimilar($aPath, $bPath){
 $aHash = ImageHash::hashImageFile($aPath);
 $bHash = ImageHash: :hashImageFile($bPath);
 return ImageHash::isHashSimilar($aHash, $bHash);
 }
}>