image compare

image compare.php

<?php
/**
* Image Comparing Function (C)2011 Robert Lerner, All Rights Reserved
* $image1                     STRING/RESOURCE          Filepath and name to PNG or passed image resource handle
* $image2                    STRING/RESOURCE          Filepath and name to PNG or passed image resource handle
* $RTolerance               INTEGER (0-/+255)     Red Integer Color Deviation before channel flag thrown
* $GTolerance               INTEGER (0-/+255)     Green Integer Color Deviation before channel flag thrown
* $BTolerance               INTEGER (0-/+255)     Blue Integer Color Deviation before channel flag thrown
* $WarningTolerance     INTEGER (0-100)          Percentage of channel differences before warning returned
* $ErrorTolerance          INTEGER (0-100)          Percentage of channel difference before error returned
 
*/
function imageCompare($image1, $image2, $RTolerance=0, $GTolerance=0, $BTolerance=0, $WarningTolerance=1, $ErrorTolerance=5)
     {
     if (is_resource($image1))
          $im = $image1;
     else
          if (!$im = imagecreatefrompng($image1))
               trigger_error("Image 1 could not be opened",E_USER_ERROR);
 
     if (is_resource($image2))
          $im2 = $image2;
     else
          if (!$im2 = imagecreatefrompng($image2))
               trigger_error("Image 2 could not be opened",E_USER_ERROR);
 
 
 
     $OutOfSpec = 0;
 
     if (imagesx($im)!=imagesx($im2))
          die("Width does not match.");
     if (imagesy($im)!=imagesy($im2))
          die("Height does not match.");
 
 
     //By columns
     for ($width=0;$width<=imagesx($im)-1;$width++)
          {
          for ($height=0;$height<=imagesy($im)-1;$height++)
               {
               $rgb = imagecolorat($im, $width, $height);
               $r1 = ($rgb >> 16) & 0xFF;
               $g1 = ($rgb >> 8) & 0xFF;
               $b1 = $rgb & 0xFF;
 
               $rgb = imagecolorat($im2, $width, $height);
               $r2 = ($rgb >> 16) & 0xFF;
               $g2 = ($rgb >> 8) & 0xFF;
               $b2 = $rgb & 0xFF;
 
               if (!($r1>=$r2-$RTolerance && $r1<=$r2+$RTolerance))
                    $OutOfSpec++;
 
               if (!($g1>=$g2-$GTolerance && $g1<=$g2+$GTolerance))
                    $OutOfSpec++;
 
               if (!($b1>=$b2-$BTolerance && $b1<=$b2+$BTolerance))
                    $OutOfSpec++;
 
 
               }
          }
     $TotalPixelsWithColors = (imagesx($im)*imagesy($im))*3;
 
     $RET['PixelsByColors'] = $TotalPixelsWithColors;
     $RET['PixelsOutOfSpec'] = $OutOfSpec;
 
     if ($OutOfSpec!=0 && $TotalPixelsWithColors!=0)
          {
          $PercentOut = ($OutOfSpec/$TotalPixelsWithColors)*100;
          $RET['PercentDifference']=$PercentOut;
          if ($PercentOut>=$WarningTolerance) //difference triggers WARNINGTOLERANCE%
               $RET['WarningLevel']=TRUE;
          if ($PercentOut>=$ErrorTolerance) //difference triggers ERRORTOLERANCE%
               $RET['ErrorLevel']=TRUE;
          }
 
     RETURN $RET;
     }


Use:
$diff = imageCompare("c:/building.png","c:/building2.png",5,5,5,1,5);
echo "<pre>";
print_r($diff);


Using these images:
Building 1 Building 2

Returns:
Array
(
     [PixelsByColors] => 19608
     [PixelsOutOfSpec] => 224
     [PercentDifference] => 1.1423908608731
     [WarningLevel] => 1
)


Interpretation of Results:
PixelsByColors = Pixel Count * 3 (for R, G, and B)
PixelsOutOfSpec = (If a pixel varies outside of xTolerance, for each red, green, and blue. Where x = R/G/B) If any channel exceeds the threshhold, this number is incremented.
PercentDifference = PixelsOutOfSpec/PixelsByColors*100
WarningLevel = TRUE (or 1) if level exceeds prescribed level
ErrorLevel = TRUE (or 1) if level exceeds prescribed level