Question

How can i find in my image the darkest pixel, which occurence in image is maximal? So to find darkest pixel which i can see more than other pixels.
Here i’m founding on my image noise, and color it with white color, but how to find darkest pixel? I try to find in rgb array element witch occurence is maximal, but so i found white pixel to. Here is part of my code:

<?php

    function components($color) {
      return array(($color >> 16) & 0xFF, ($color >> 8) & 0xFF, $color & 0xFF);
    }

    // Performs "similarity test" of 2 colors
    function isSimilar($color1, $color2) {
      $c1 = components($color1);
      $c2 = components($color2);
      for ($i = 0; $i < 3; $i++) {
        $k = ($c1[$i] > $c2[$i]) ? ($c1[$i] - $c2[$i]) / $c2[$i] : ($c2[$i] - $c1[$i]) / $c1[$i];
        if ($k > 0.35) return false;
      }
      return true;
    }

    function LoadJpeg($imgname)
    {
        $count = 0;
        /* Attempt to open */
        $im = @imagecreatefrompng($imgname);
        $imagedata = getimagesize($imgname);

        $n = $imagedata[0];
        $m = $imagedata[1];
        for($i=0; $i<$imagedata[0]; $i++){
            for($j=0; $j<$imagedata[1]; $j++){
                $rgb[$i][$j] = imagecolorat($im, $i, $j);
                //echo $rgb[$i][$j];
                //echo "<br>";
            }
        }



    /*    for ($k = 0; $k < $n; $k++)
        {
            for ($l = 0; $l < $m; $l++)
            {
                for ($i = 0; $i < $n; $i++)
                {
                    for ($j = 0; $j < $m; $j++)
                    {
                        if (($i+1 == $n) && ($j+1 == $m))
                        {
                            continue;
                        }
                        else
                        {
                            if ($j+1 == $m and $rgb[$i][$j] > $rgb[$i+1][0])
                            {
                                $t = $rgb[$i][$j];
                                $rgb[$i][$j] = $rgb[$i+1][0];
                                $rgb[$i+1][0] = $t;
                            }
                            else
                            {
                                if ($rgb[$i][$j] > $rgb[$i][$j+1])
                                {
                                    $t = $rgb[$i][$j];
                                    $rgb[$i][$j] = $rgb[$i][$j+1];
                                    $rgb[$i][$j+1] = $t;
                                }
                            }
                        }
                    }
                }
            }
        }*/



        for($i=0; $i<$imagedata[0]-3; $i++){
            for($j=0; $j<$imagedata[1]-3; $j++){
                if (isSimilar($rgb[$i][$j], $rgb[$i][$j + 3]) or isSimilar($rgb[$i][$j], $rgb[$i + 3][$j])) 
                {
                    #echo "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAa";
                    $count = $count + 1;
                    //echo "<br> <br>";
                    //echo $count;
                    //$red = imagecolorallocate($im, 255, 255, 255);

                    imagesetpixel($im, $i, $j, 16777215);
                    cropCentered($im,20,20);
                }                  

            }
        }

        return $im;
    }

    function cropCentered($img, $w, $h)
    {
      $cx = $img->getWidth() / 2;
      $cy = $img->getHeight() / 2;
      $x = $cx - $w / 2;
      $y = $cy - $h / 2;
      if ($x < 0) $x = 0;
      if ($y < 0) $y = 0;
      return $img->crop(0, 0, $w, $h);
    }

    header('Content-Type: image/jpeg');

    $img = LoadJpeg('1.png');




    imagejpeg($img,null, 100);

    ?>

Answer 1

You need to use a color model different than RGB – in this case HSL is useful, because it contains “Lightness” component. Based on this component we can judge whether some color is lighter or darker than another. There are several methods of converting RGB to HSL, I’ve used the one described in the Wikipedia article (see HSL “bi-hexcone” model):

<?php

// Returns whether c2 is darker than c1
function isDarker($c1, $c2) {
  // Find L (lightness) component in a HSL model
  $max1 = max($c1);
  $min1 = min($c1);
  $l1 = ($max1 + $min1) / 2;
  $max2 = max($c2);
  $min2 = min($c2);
  $l2 = ($max2 + $min2) / 2;

  // Compare colors based on L component (lower means darker)
  return $l2 < $l1;
}

// Assuming colors are stored in a 2-dimensional $rgb array
$rowCount = count($rgb);
$colCount = count($rgb[0]);
$darkest = $rgb[0][0];
for ($i = 0; $i < $rowCount; $i++) {
  for ($j = 0; $j < $colCount; $j++) {
    if (isDarker($darkest, $rgb[$i][$j])) {
      $darkest = $rgb[$i][$j];
      // Optionally you can save the indices $i and $j
    }
  }
}