imagediff.php

<?php

/* ImageDiff --------------------------------------------
Class to identify difference between two images.
Difference is identified in comparing the delta between average color.
Based on idea from:
http://www.hackerfactor.com/blog/?/archives/432-Looks-Like-It.html

call function Diff to get an Array with the results
Diff Description:
Array Diff( string $im1, string $im2 [, boolean $save[, integer $size]] ):
$im1: Path to first file
$im2: Path to second file
$save: Saves the compare images in the same folder than the soruce file1
details are returned back in the array.
$size: defines the resize image size which is used to compare.
default is 16 pixels, Higher = more Detail, but slower

Example:
$clIM = new ImageDiff;
$ret = clIM->Diff("./images/image1.jpg","./images/image2.jpg", true)
print_r($ret);
*/


class ImageDiff {

    public $dbg = false;

    public function Diff($im1, $im2, $save = false, $size = 16) {
// $im1, $im2 = path to two images
// $size default 8, resize size for delta processing
// $save default. saves the resized images (), same target as src with prefix sized_
        $dbg = $this->dbg;

// Vergleichsbilder erzeugen Nr. 1
        $i1 = imagecreatefromjpeg($im1);
        list($width1, $height1) = getimagesize($im1);
        $id1 = imagecreatetruecolor($size, $size);
        imagecopyresized($id1, $i1, 0, 0, 0, 0, $size, $size, $width1, $height1);
        imagefilter($id1, IMG_FILTER_GRAYSCALE);

// Vergleichsbilder erzeugen Nr. 2
        $i2 = imagecreatefromjpeg($im2);
        list($width2, $height2) = getimagesize($im2);
        $id2 = imagecreatetruecolor($size, $size);
        imagecopyresized($id2, $i2, 0, 0, 0, 0, $size, $size, $width2, $height2);
        imagefilter($id2, IMG_FILTER_GRAYSCALE);

// Nun Pixel
        $i1_avg = $this->average($id1);
        $i2_avg = $this->average($id2);

//Compute Hash
        $i1_hash = $this->ComputeHash($id1, $i1_avg);
        if ($dbg) echo "Hash Bild 1 : " . implode($i1_hash) . " <br>";

        $i2_hash = $this->ComputeHash($id2, $i2_avg);
        if ($dbg) echo "Hash Bild 2 : " . implode($i2_hash) . " <br>";

// Count Distance:
        $fail = 0;
        for ($x = 0; $x < count($i2_hash); $x++) {
            if ($i2_hash[$x] != $i1_hash[$x]) {
                $fail++;
            }
        }
        $delta = ($fail / ($size * $size)) * 100;
        if ($save) {
// Create Delta image
            $id3 = imagecreatetruecolor($size, $size);
            imagecopy($id3, $id1, 0, 0, 0, 0, $size, $size);
            $col = imagecolorallocate($id3, 0, 255, 0);
            $x = $y = 0;
            $cnt = 0;
            for ($y = 0; $y < $size; $y++) {
                for ($x = 0; $x < $size; $x++) {
                    if ($i2_hash[$cnt] != $i1_hash[$cnt]) {
                        imagesetpixel($id3, $x, $y, $col);
                    }
                    $cnt++;
                }
            }
            $fndelta = pathinfo($im1, PATHINFO_DIRNAME) . "/delta_" . basename($im1);
            imagejpeg($id3, $fndelta);
            $ret["deltaimage"] = $fndelta;

// Save temporary images
            $fn1 = pathinfo($im1, PATHINFO_DIRNAME) . "/sized_" . basename($im1);
            $fn2 = pathinfo($im2, PATHINFO_DIRNAME) . "/sized_" . basename($im2);
            imagejpeg($id1, $fn1);
            imagejpeg($id2, $fn2);
            $ret["tempimg1"] = $fn1;
            $ret["tempimg2"] = $fn2;
        }
        $ret["delta"] = $delta;
        return $ret;
    }

    private function average($img) {
        $w = imagesx($img);
        $h = imagesy($img);
        $r = $g = $b = 0;
        for ($y = 0; $y < $h; $y++) {
            for ($x = 0; $x < $w; $x++) {
                $rgb = imagecolorat($img, $x, $y);
                $r += $rgb >> 16;
//$g += $rgb >> 8 & 255;
//$b += $rgb & 255;
            }
        }
        $pxls = $w * $h;
//$r = (round($r / $pxls));
//$g = (round($g / $pxls));
        $r = (round($r / $pxls)); // Da wir graustufen verwenden reicht eine Farbe
//return $r ."," . $g .",". $b;
        if ($r < 10) $r = 0; // Wenn fast Schwarz, dann schwarz!
        if ($r > 245) $r = 255; // auch mit Weiß so verfahren.
        return $r;
    }

    private function ComputeHash($img, $avg = 100) {
        global $dbg;
        $w = imagesx($img);
        $h = imagesy($img);
        $r = $g = $b = 0;
        for ($y = 0; $y < $h; $y++) {
            for ($x = 0; $x < $w; $x++) {
                $rgb = imagecolorat($img, $x, $y);
                $r = $rgb >> 16;
                if ($r <= $avg) {
                    $hash [] = "1";
                } else {
                    $hash [] = "0";
                }
            }
        }
        return $hash;
    }

}