PHP implements image similarity comparison

How to achieve image similarity comparison in PHP? This article will use perceptual hashing algorithm to search for similar pictures. I hope to be helpful.

The advantage of perceptual hashing is that it is simple and fast and is not affected by the scaling of the image size. The disadvantage is that the content of the image cannot be changed. In practical applications, the more powerful pHash algorithm and SIFT algorithm are often used, which can identify the deformation of images. As long as the distortion does not exceed 25%, they can match the original image.

Perceptual Hash Algorithm

count 9a81a7c8cf5e76ae894ce819e4b9b4ee 10 two different images
var_dump(ImageHash:: run('./1.png', './psb.jpg'));

<?php
class ImageHash {
  const FILE_NOT_FOUND = &#39;-1&#39;;
  const FILE_EXTNAME_ILLEGAL = &#39;-2&#39;;
  private function __construct() {}
  public static function run($src1, $src2) {
    static $self;
    if(!$self) $self = new static;
    if(!is_file($src1) || !is_file($src2)) exit(self::FILE_NOT_FOUND);
    $hash1 = $self->getHashValue($src1);
    $hash2 = $self->getHashValue($src2);
    if(strlen($hash1) !== strlen($hash2)) return false;
    $count = 0;
    $len = strlen($hash1);
    for($i = 0; $i < $len; $i++) if($hash1[$i] !== $hash2[$i]) $count++;
    return $count <= 10 ? true : false;
  }
  public function getImage($file) {
    $extname = pathinfo($file, PATHINFO_EXTENSION);
    if(!in_array($extname, [&#39;jpg&#39;,&#39;jpeg&#39;,&#39;png&#39;,&#39;gif&#39;])) exit(self::FILE_EXTNAME_ILLEGAL);
    $img = call_user_func(&#39;imagecreatefrom&#39;. ( $extname == &#39;jpg&#39; ? &#39;jpeg&#39; : $extname ) , $file);
    return $img;
  }
  public function getHashValue($file) {
    $w = 8;
    $h = 8;
    $img = imagecreatetruecolor($w, $h);
    list($src_w, $src_h) = getimagesize($file);
    $src = $this->getImage($file);
    imagecopyresampled($img, $src, 0, 0, 0, 0, $w, $h, $src_w, $src_h);
    imagedestroy($src);
    $total = 0;
    $array = array();
    for( $y = 0; $y < $h; $y++) {
      for ($x = 0; $x < $w; $x++) {
        $gray = (imagecolorat($img, $x, $y) >> 8) & 0xFF;
        if(!isset($array[$y])) $array[$y] = array();
        $array[$y][$x] = $gray;
        $total += $gray;
      }
    }
    imagedestroy($img);
    $average = intval($total / ($w * $h * 2));
    $hash = &#39;&#39;;
    for($y = 0; $y < $h; $y++) {
      for($x = 0; $x < $w; $x++) {
        $hash .= ($array[$y][$x] >= $average) ? &#39;1&#39; : &#39;0&#39;;
      }
    }
    var_dump($hash);
    return $hash;
  }
}
var_dump(ImageHash::run(&#39;./1.png&#39;, &#39;./psb.jpg&#39;));

Method 2:

hash($f);
 }
 return $isString ? $result[0] : $result;
 }
 public function checkIsSimilarImg($imgHash, $otherImgHash){
 if (file_exists($imgHash) && file_exists($otherImgHash)){
  $imgHash = $this->run($imgHash);
  $otherImgHash = $this->run($otherImgHash);
 }
 if (strlen($imgHash) !== strlen($otherImgHash)) return false;
 $count = 0;
 $len = strlen($imgHash);
 for($i=0;$i<$len;$i++){
  if ($imgHash{$i} !== $otherImgHash{$i}){
  $count++;
  }
 }
 return $count <= (5 * $rate * $rate) ? true : false;
 }
 public function hash($file){
 if (!file_exists($file)){
  return false;
 }
 $height = 8 * $this->rate;
 $width = 8 * $this->rate;
 $img = imagecreatetruecolor($width, $height);
 list($w, $h) = getimagesize($file);
 $source = $this->createImg($file);
 imagecopyresampled($img, $source, 0, 0, 0, 0, $width, $height, $w, $h);
 $value = $this->getHashValue($img);
 imagedestroy($img);
 return $value;
 }
 public function getHashValue($img){
 $width = imagesx($img);
 $height = imagesy($img);
 $total = 0;
 $array = array();
 for ($y=0;$y<$height;$y++){
  for ($x=0;$x<$width;$x++){
  $gray = ( imagecolorat($img, $x, $y) >> 8 ) & 0xFF;
  if (!is_array($array[$y])){
   $array[$y] = array();
  }
  $array[$y][$x] = $gray;
  $total += $gray;
  }
 }
 $average = intval($total / (64 * $this->rate * $this->rate));
 $result = &#39;&#39;;
 for ($y=0;$y<$height;$y++){
  for ($x=0;$x<$width;$x++){
  if ($array[$y][$x] >= $average){
   $result .= &#39;1&#39;;
  }else{
   $result .= &#39;0&#39;;
  }
  }
 }
 return $result;
 }
 public function createImg($file){
 $ext = $this->getFileExt($file);
 if ($ext === &#39;jpeg&#39;) $ext = &#39;jpg&#39;;
 $img = null;
 switch ($ext){
  case &#39;png&#39; : $img = imagecreatefrompng($file);break;
  case &#39;jpg&#39; : $img = imagecreatefromjpeg($file);break;
  case &#39;gif&#39; : $img = imagecreatefromgif($file);
 }
 return $img;
 }
 public function getFileExt($file){
 $infos = explode(&#39;.&#39;, $file);
 $ext = strtolower($infos[count($infos) - 1]);
 return $ext;
 }
}

The calling method is as follows:

 require_once "Imghash.class.php";
$instance = ImgHash::getInstance();
$result = $instance->checkIsSimilarImg('chenyin/IMG_3214.png', 'chenyin/IMG_3212.JPG');

If the $result value is true, it indicates that the two pictures are similar, otherwise they are not similar.

Related recommendations:

php image operation class, supports generating thumbnails, adding watermarks, and uploading thumbnails

Strong PHP image processing class

What does thumbs mean PHPThumb PHP picture thumbnail gallery

The above is the detailed content of PHP implements image similarity comparison. For more information, please follow other related articles on the PHP Chinese website!