scan_jpeg.php

# code from - https://github.com/pmeenan/progressive-scans
# get the size of each scan of a progressive jpeg
<?php
function GetImageScans($src, &$info) {
    $scans = null;
    if (is_file($src)) {
        $size = getimagesize($src);
        $info['src'] = $src;
        $info['size'] = filesize($src);
        $info['width'] = $size[0];
        $info['height'] = $size[1];
        $file = fopen($src, 'rb');
        if ($file) {
            $bytes = fread($file, $info['size']);
            // process the jpeg markers
            $i = 0;
            $scan_start = 0;
            $size = strlen($bytes);
            $try = 0;
            while (FindNextScan($bytes, $size, $i)) {
                $scan_length = $i - $scan_start;
                $ratio = $scan_length/$info['size'] * 100;
                $try++;
                $output = printf("scan No. %d, bytes = %d (%0.2f%%) \n", $try, $scan_length, $ratio);
                $scans[] = substr($bytes, $scan_start, $scan_length);
                $scan_start = $i;
            }
            fclose($file);
        }
    }
    return $scans;
}
function FindNextScan(&$bytes, $size, &$i) {
    $found = false;
    if ($i < $size) {
        while (!$found && FindNextMarker($bytes, $size, $i, $marker, $marker_length)) {
            if (bin2hex($marker) == 'ffda') {
                $found = true;
            }
            $i += $marker_length;
        }
        if (!$found) {
            $found = true;
            $i = $size;
        }
    }
    return $found;
}
function FindNextMarker(&$bytes, $size, &$i, &$marker, &$marker_length) {
    $marker_length = 0;
    $marker = null;
    $found = false;
    $nolength = array('d0','d1','d2','d3','d4','d5','d6','d7','d8','d9','01');
    $sos = 'da';
    if ($i < $size) {
      $val = dechex(ord($bytes[$i]));
      if ($val == 'ff') {
          $marker = $bytes[$i];
          // ff can repeat, the actual marker comes from the first non-ff
          while ($val == 'ff') {
            $i++;
            $val = dechex(ord($bytes[$i]));
          }
          $marker .= $bytes[$i];
          $i++;
          if (in_array($val, $nolength)) {
              $found = true;
          } elseif($val == $sos) {
              // image data
              $j = $i + 1;
              $next_marker = $size;
              while ($j < $size - 1 && !$found) {
                  $val = dechex(ord($bytes[$j]));
                  if ($val == 'ff') {
                      $k = $j + 1;
                      $val = dechex(ord($bytes[$k]));
                      if ($val != '00') {   // escaping
                        while ($k < $size = 1 && $val == 'ff') {
                            $k++;
                            $val = dechex(ord($bytes[$k]));
                        }
                        $next_marker = $j;
                        $found = true;
                      }
                  }
                  $j++;
              }
              $marker_length = $next_marker - $i;
          } elseif ($i + 1 < $size) {
            $l1 = ord($bytes[$i]);
            $l2 = ord($bytes[$i+1]);
            $marker_length = $l1 * 256 + $l2;
            $found = true;
          }
      }
    }
    return $found;
}

$info = [];
GetImageScans($argv[1], $info);

?>