php/lib_dta/index_page_make.php

<?php
//--------------------------------------------------------------------------------
//index_page_make.php, v0.1a, Copyright David T. Ashley, 2015
//--------------------------------------------------------------------------------
//This program, a PHP script, reduces all .JPG images in a directory to create
//thumbnails, and creates a PHP index script that will display thumbnails of
//all the images with the thumbnails linking to the full-sized images.  This
//script is used by David T. Ashley to make web pages out of large numbers of
//images downloaded from digital cameras.  The PHP index script created by this
//program is typically manually edited after it is created to add comments about
//what the pictures are.
//
//Although this program is for Dave Ashley's specific uses, it should be easy
//enough to customize, and it provides an example of how to manipulate images
//using the ImageMagick library compiled into PHP.
//
//This script is designed to be run manually (rather than automatically invoked
//as a result of a web page request).  It was written in PHP for convenience
//simply because DreamHost (the web hosting company Dave Ashley uses) has as part
//of its hosting environment PHP with the ImageMagick library compiled in.
//
//Usually, invoke this script using "php index_page_make.php", but the method
//of invocation may vary based on computing platform details.
//--------------------------------------------------------------------------------
//TODO for this script:
//   a)The configuration options should just be defaults, and it should be
//     possible to override them selectively via command-line options.
//   b)Many digital cameras and phones include information in the JPG
//     headers, and it would be handy to use (and not use) that information
//     in the following ways:
//        b1)Date taken--appear in ALT and TITLE so it can be seen on
//           mouseover of the thumbnail.
//        b2)Location--same as (b1).
//        b3)Orientation--tempting to use this, but the web page designer
//           has to have final say about how to lay the web page out, including
//           photo orientation.
//--------------------------------------------------------------------------------
//This program is free software: you can redistribute it and/or modify
//it under the terms of the GNU General Public License as published by
//the Free Software Foundation, either version 3 of the License, or
//(at your option) any later version.
//
//This program is distributed in the hope that it will be useful,
//but WITHOUT ANY WARRANTY; without even the implied warranty of
//MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//GNU General Public License for more details.
//
//You should have received a copy of the GNU General Public License
//along with this program.  If not, see http://www.gnu.org/licenses/.
//--------------------------------------------------------------------------------
//C O N F I G U R A T I O N
//--------------------------------------------------------------------------------
//Configuration switches were not tested.  E-mail me any script corrections
//(dashley@gmail.com).
define ("CFG_THUMBNAIL_DIMENSION_MAX", 125);
   //The maximum dimension of the created thumbnails.  Thumbnails are sized so
   //that the longest dimension is this many pixels.
define ("CFG_IMAGE_LC_CONVERT", TRUE);
   //TRUE if should convert existing image file names to lower case, FALSE
   //otherwise.
define ("CFG_THUMBNAIL_BEVELED_BORDER_WIDTH", 4);
   //The number of pixels that the thumbnail beveled borders should be.
define ("CFG_THUMBNAIL_FILENAME_SUFFIX", "_small");
   //String added just before the filename extension to choose thumbnail names
   //based on name of full-sized image.
define ("CFG_LANCZOS_FILTER_APPLY", TRUE);
   //TRUE if should apply the Lanczos filter when making the thumbnail, FALSE
   //otherwise.  I have no idea if using a Lanczos filter improves the quality
   //of the thumbnails, but the filter was applied in the PHP example I found
   //online.  Applying the Lanczos filter typically adds a few seconds to the
   //time required to create each thumbnail.
define ("CFG_DTA_PHP_INDEX_CREATE", TRUE);
   //TRUE if should create a PHP index page that serves Dave Ashley's needs,
   //or FALSE to create a plain vanilla text file with HTML.
define ("CFG_PHP_INDEX_FILE_NAME",  "index2.php");
define ("CFG_HTML_INDEX_FILE_NAME", "index2.txt");
   //File names to use.  Only one of the two will be used, depending on the
   //CFG_DTA_PHP_INDEX_CREATE setting.
define ("CFG_CONSOLE_STD_LINE_LEN", 78);
   //Number of characters per line preferred for console output.
define ("CFG_INDEX_PARAGRAPH_INDENT", 0);
   //For the created index file (either PHP or plain HTML), the number of 
   //characters that the <p> and </p> tags should be indented.
define ("CFG_INDEX_LINK_INDENT", 0);
   //For the created index file, the number of characters that the <a>
   //tags should be indented.
//--------------------------------------------------------------------------------
//Calculates important integer indices related to creating a thumbnail, in order
//to minimize distortion in the thumbnail.
//
//When creating a thumbnail, the longer side may be relatively short (perhaps
//100 pixels), and the shorter side may be even shorter (perhaps even as short
//as 10 pixels).  If the dimensions of the original image were not changed,
//converting the image to a thumbnail may result in distortion of up to about
//one percent.  As an example, suppose that a 1600 x 900 image is converted to a
//thumbnail with the longer side of 125 pixels.  The ideal dimension for the
//shorter side would be (900/1600) * 125 = 70.3125 pixels.  The aspect ratio of
//the thumbnail can't be made to match the aspect ratio of the original image.
//
//To avoid any aspect ratio distortion that might be noticeable, this program
//chooses the shorter dimension for the thumbnail that is the ceiling of the actual
//quotient, then crops the longer dimension of the original image before the
//conversion to try and match the aspect ratios as closely as possible.
//
//In the example a paragraph or two above, the shorter side of the thumbnail
//would be chosen to be 71 pixels.
//
//Once this choice is made, we want to trim the original image before conversion
//so that n/900 is as close as possible to 125/71.  n = (900 * 125) / 71 = 
//1584.5070 pixels, so we choose 1585.  This keeps the aspect ratio of the 
//original image and the thumbnail as close as possible.
//
//Although the longer side of the original image may be reduced prior to the
//conversion to a thumbnail, this information is not written to disk, and
//the original image is not modified.  The adjustment of the longer side is
//just a conversion trick to hopefully get better thumbnails. 
function calc_thumbnail_conversion_pars
         (
           $in_orig_longer,
              //Longer dimension of original image.
           $in_orig_shorter,
              //Shorter dimension of original image.
           $in_thumbnail_longer,
              //Longer dimension of desired thumbnail.
         & $out_thumbnail_longer,
              //Longer dimension of thumbnail that should be created.
         & $out_thumbnail_shorter,
              //Shorter dimension of thumbnail that should be created.
         & $out_orig_crop_dim_longer,
              //The size to crop to on the longer axis of the original.
         & $out_orig_crop_dim_shorter,
              //The size to crop to on the shorter axis of the original.
         & $out_orig_crop_start_longer,
              //For use with the Imagick:cropImage() method, the start
              //position of the crop on the longer axis.
         & $out_orig_crop_start_shorter
              //For use with the Imagick:cropImage() method, the start
              //position of the crop on the shorter axis.
         )
{
   //Set the thumbnail shorter dimension to the floor.  This means would need to trim
   //longest dimension of original to match aspect ratio as closely as possible.
   $out_thumbnail_longer        = $in_thumbnail_longer;
   $out_thumbnail_shorter       = ceil(((float)$in_thumbnail_longer * 
                                  (float)$in_orig_shorter) / (float)$in_orig_longer);
   settype($out_thumbnail_shorter, "integer");

   //The aspect ratio of the thumbnail is now set.  Try to match the aspect ratio of the larger
   //image as closely as possible by selecting a smaller number for the long axis of the
   //original image.
   $out_orig_crop_dim_longer = round(((float)$in_thumbnail_longer * 
                               (float)$in_orig_shorter) / (float)$out_thumbnail_shorter);
   settype($out_orig_crop_dim_longer, "integer");

   //The original keeps its shorter dimension unchanged.
   $out_orig_crop_dim_shorter   = $in_orig_shorter;

   //Set the cropping of the longer side of the original to cover half the necessary
   //reduction.
   $out_orig_crop_start_longer  = round(((float)$in_orig_longer - 
                                  (float)$out_orig_crop_dim_longer) / 2.0);
   settype($out_orig_crop_start_longer, "integer");

   //No cropping of original shorter side.
   $out_orig_crop_start_shorter = 0;
}
//--------------------------------------------------------------------------------
//Repeats a character to the console output a certain number of times.
function rep_char_con($c, $n)
{
   while ($n--)
      echo $c;
}
//--------------------------------------------------------------------------------
//Writes a standard thick horizontal line to the console.
function hor_line_thick()
{
   rep_char_con("=", CFG_CONSOLE_STD_LINE_LEN);
   echo "\n";
}
//--------------------------------------------------------------------------------
//Writes a standard thin horizontal line to the console.
function hor_line_thin()
{
   rep_char_con("-", CFG_CONSOLE_STD_LINE_LEN);
   echo "\n";
}
//--------------------------------------------------------------------------------
//Returns the name of the file that should be used for the index.
function index_file_name()
{
  if (CFG_DTA_PHP_INDEX_CREATE)
     return CFG_PHP_INDEX_FILE_NAME;
  else
     return CFG_HTML_INDEX_FILE_NAME;
}

//--------------------------------------------------------------------------------
//Checks if the index file already exists, returns TRUE if so, or FALSE otherwise.
//Because the sole purpose of this function is to refuse to write over an
//existing index file, it will also return true if a directory of the target
//name exists.
function index_file_or_dir_exists()
{
   return file_exists(index_file_name());
}
//--------------------------------------------------------------------------------
//Returns an array of all files in the working directory.
//If no files can be found, returns FALSE.
function get_file_names_in_dir()
{
   //Get directory list.
   $rv = scandir (".");

   //If the list is empty, something went wrong.  Return FALSE.
   if ($rv === FALSE)
      return FALSE;

   return $rv;
}
//--------------------------------------------------------------------------------
//Returns TRUE if a file name appears to be a valid .JPG file name, or FALSE
//otherwise.
function is_valid_jpg_file_name($s)
{
   //First, the file name has to be AT LEAST 5 characters long.  This would
   //be a short name like "x.jpg".
   if (strlen($s) < 5)
      return FALSE;

   //Convert the string name to all lower case.
   $s = strtolower($s);

   //If the final 4 characters are .jpg, we call it good.  We've already
   //verified that the string is at least of length 5.
   $s2 = substr($s, strlen($s) - 4);
   if (strcmp($s2, ".jpg") == 0)
      return TRUE;

   //The only remaining possibility for validity is that the string is of the
   //form ".jpeg".  Check for this.
   //The file name has to be AT LEAST 6 characters long.  This would
   //be a short name like "x.jpeg".
   if (strlen($s) < 6)
      return FALSE;

   //If the final 5 characters are .jpeg, we call it good.  We've already
   //verified that the string is at least of length 6.
   $s2 = substr($s, strlen($s) - 5);
   if (strcmp($s2, ".jpeg") == 0)
      return TRUE;

   //If we are here, not a valid .jpg file name.
   return FALSE;
}
//--------------------------------------------------------------------------------
//As a function of the file name, creates the file name for the thumbnail.
function file_name_to_thumbnail_name($in_filename)
{
   $extension_start = strrpos($in_filename, ".");
      //Find position of last "." in string.  This should precede the
      //file extension.
   if ($extension_start === FALSE)
   {
      //"." not found.  Should not happen.  Filenames were checked in advance.
      echo "Fatal internal error at line " . __LINE__ . "\n";
      exit(1);
   } 

   $filename_prefix    = substr($in_filename, 0, $extension_start);
   $filename_extension = substr($in_filename, $extension_start);

   $rv = $filename_prefix . CFG_THUMBNAIL_FILENAME_SUFFIX . $filename_extension;

   return $rv;
}
//--------------------------------------------------------------------------------
//Writes the index file preamble to the index file.  This is very much
//dependent on how the thumbnails will be used.  This is currently customized
//for what Dave Ashley does.
function write_index_file_preamble($handle)
{
   fwrite($handle, "<" . "?" . "php\n");
   fwrite($handle, "require_once(\"style/std/stdwpstyle.inc\");\n");
   fwrite($handle, "?" . ">" . "\n");
   fwrite($handle, "<" . "?" . "php\n");
   fwrite($handle, "   $" . "thispage = new StdWpStyle();\n");
   fwrite($handle, "\n");
   fwrite($handle, "   $" . "thispage->static_page_header_title_std(\"TBD\",\n");
   fwrite($handle, "                                           \"TBD\",\n");
   fwrite($handle, "                                           \"\");\n");
   fwrite($handle, "   $" . "thispage->static_page_photo_thumbnail_explanation(TRUE, TRUE);\n");
   fwrite($handle, "?" . ">" . "\n");
   for ($i = 0; $i < CFG_INDEX_PARAGRAPH_INDENT; $i++)
   {
      fwrite($handle, " ");
   }
   fwrite($handle, "\n<p align=\"center\">\n");
}
//--------------------------------------------------------------------------------
//Writes the index file postamble to the index file.  This is very much
//dependent on how the thumbnails will be used.  This is currently customized
//for what Dave Ashley does.
function write_index_file_postamble($handle)
{
   for ($i = 0; $i < CFG_INDEX_PARAGRAPH_INDENT; $i++)
   {
      fwrite($handle, " ");
   }
   fwrite($handle, "</p>\n\n");
   fwrite($handle, "<" . "?" . "php\n");
   fwrite($handle, "   $" . "thispage->static_page_footer_std();\n");
   fwrite($handle, "?" . ">" . "\n");
}
//--------------------------------------------------------------------------------
//Actually creates the thumbnail, and returns some information about what was
//done.
//
//The calls to the ImagMagick library take on the order of 5s per image if there
//is filtering.
function create_thumbnail(  $in_filename, 
                            $in_thumbnailname,
                          & $out_filename_filesize,
                          & $out_filename_xdim,
                          & $out_filename_ydim,
                          & $out_thumbnailname_filesize,
                          & $out_thumbnailname_xdim,
                          & $out_thumbnailname_ydim)
{
   //Assign output parameters just in case something doesn't get assigned.
   $out_filename_filesize      = 0;
   $out_filename_xdim          = 0;
   $out_filename_ydim          = 0;
   $out_thumbnailname_filesize = 0;
   $out_thumbnailname_xdim     = 0;
   $out_thumbnailname_ydim     = 0;

   //Establish target dimensions.  Two cases, depending on which is the longer
   //side.

   //Construct.
   $imagick = new Imagick();

   //Load image.
   $imagick->readImage($in_filename);

   //Get the dimensions of the image we just loaded.
   $geo               = $imagick->getImageGeometry(); 
   $out_filename_xdim = $geo['width']; 
   $out_filename_ydim = $geo['height']; 

   //Calculate target sizes.  We rearrange parameters based on which is our
   //longest side.
   if ($out_filename_xdim >= $out_filename_ydim)
   {
      //Longer width (x-dimension), or square.
      calc_thumbnail_conversion_pars
         (
         $out_filename_xdim,
         $out_filename_ydim,
         CFG_THUMBNAIL_DIMENSION_MAX,
         $out_thumbnailname_xdim,
         $out_thumbnailname_ydim,
         $orig_crop_dim_x,
         $orig_crop_dim_y,
         $orig_crop_start_x,
         $orig_crop_start_y
         );
   }
   else
   {
      //Longer height (y-dimension).
      calc_thumbnail_conversion_pars
         (
         $out_filename_ydim,
         $out_filename_xdim,
         CFG_THUMBNAIL_DIMENSION_MAX,
         $out_thumbnailname_ydim,
         $out_thumbnailname_xdim,
         $orig_crop_dim_y,
         $orig_crop_dim_x,
         $orig_crop_start_y,
         $orig_crop_start_x
         );
   }

   //For debugging only, might want to know intermediate calculation results.
   //echo "xcropdim, ycropdim, xcropstart, ycropstart: "
   //     .
   //     $orig_crop_dim_x
   //     .
   //     " "
   //     . 
   //     $orig_crop_dim_y
   //     .
   //     " "
   //     . 
   //     $orig_crop_start_x
   //     .
   //     " "
   //     . 
   //     $orig_crop_start_y
   //     .
   //     "\n";
           
   //Crop the original to try to preserve the aspect ratio of the thumbnail
   //as precisely as possible.
   $imagick->cropImage( 
                      $orig_crop_dim_x, 
                      $orig_crop_dim_y,
                      $orig_crop_start_x,
                      $orig_crop_start_y
                      );

   //For debugging only, might want to get a look at the cropped image, to
   //be sure nothing unexpected happens on the canvas.
   //$imagick->writeImage($in_filename . ".cropped.jpg");

   //Resize to thumbnail size.
   if (CFG_LANCZOS_FILTER_APPLY)
   {
      $imagick->resizeImage($out_thumbnailname_xdim, 
                            $out_thumbnailname_ydim, 
                            Imagick::FILTER_LANCZOS, 
                            1);
   }
   else
   {
      $imagick->resizeImage($out_thumbnailname_xdim, 
                            $out_thumbnailname_ydim, 
                            0, 
                            1);
   }

   //Create the border.
   $imagick->raiseImage(CFG_THUMBNAIL_BEVELED_BORDER_WIDTH, 
                        CFG_THUMBNAIL_BEVELED_BORDER_WIDTH, 
                        0, 
                        0, 
                        1);

   //Set compression to get a smaller thumbnail written, and strip
   //header information.  stripImage() seems to have the largest effect
   //on thumbnail file size, so leaving the thumbnail quality near 100%
   //is feasible.  The jump in file size between 90% and 95% seemed to be
   //fairly large (40% to 50%), so I left it at 90%.  My rationale is
   //that with the proliferation of mobile devices and cellular data,
   //getting the thumbnail as small as possible is more important than
   //the thumbnail looking perfect.  If the viewer wants a perfect image,
   //they can view the full-sized image.
   $imagick->setImageCompression(Imagick::COMPRESSION_JPEG); 
   $imagick->setImageCompressionQuality(90);
   $imagick->stripImage(); 

   //Write the thumbnail.
   $imagick->writeImage($in_thumbnailname);

   //Destroy to prevent memory leak.
   $imagick->clear(); 
   $imagick->destroy(); 

   //All of the writing is done.  Try to obtain the file sizes.
   $fsize = filesize($in_filename);
   if ($fsize !== FALSE)
      $out_filename_filesize = $fsize;
   $fsize = filesize($in_thumbnailname);
   if ($fsize !== FALSE)
      $out_thumbnailname_filesize = $fsize;
}
//--------------------------------------------------------------------------------
//Writes a line to the index file corresponding to a linked larger picture
//reprsented by a thumbnail.
function write_index_line(  $handle,
                            $filename, 
                            $thumbnailname,
                            $filename_filesize,
                            $filename_xdim,
                            $filename_ydim,
                            $thumbnailname_filesize,
                            $thumbnailname_xdim,
                            $thumbnailname_ydim)
{
//<a href="dscn1258.jpg"><img border="0" src="dscn1258_small.jpg" alt="dscn1258.jpg (4932338 bytes)" width="125" height="93"></a>
   //Indent.
   for ($i = 0; $i < CFG_INDEX_LINK_INDENT; $i++)
   {
      fwrite($handle, " ");
   }

   fwrite($handle, "<a href=\"");
   fwrite($handle, $filename);
   fwrite($handle, "\"><img border=\"0\" src=\"");
   fwrite($handle, $thumbnailname);
   fwrite($handle, "\" alt=\"");
   fwrite($handle, $filename);
   fwrite($handle, " (");
   fwrite($handle, $filename_filesize);
   fwrite($handle, " bytes)\" ");
   fwrite($handle, "title=\"");
   fwrite($handle, $filename);
   fwrite($handle, " (");
   fwrite($handle, $filename_filesize);
   fwrite($handle, " bytes)\" width=\"");
   fwrite($handle, $thumbnailname_xdim);
   fwrite($handle, "\" height=\"");
   fwrite($handle, $thumbnailname_ydim);
   fwrite($handle, "\"></a>");
   fwrite($handle, "\n");
}
//--------------------------------------------------------------------------------
   //Write introductory message.
   hor_line_thick();
   echo "Execution begins.\n";
   hor_line_thin();
   //-----------------------------------------------------------------------------
   //End the script of the index file already exists.  Don't want to overwrite
   //anything that may be valuable to the user.
   if (index_file_or_dir_exists())
   {
      echo "Index file \"" . index_file_name() . "\" already exists.\n";
      echo "Script cannot continue.  Exiting.\n";
      exit(1);
   }
   else
   {
      echo "Index file \"" . index_file_name() . "\" does not exist.  " .
      "Continuing.\n";
   }
   hor_line_thin();
   //-----------------------------------------------------------------------------
   //Get and emit the names of everything in the directory.
   $file_list = get_file_names_in_dir();
   if ($file_list === FALSE)
   {
      echo "List of files from PHP function scandir() is empty.\n";
      echo "Serious internal error, or nothing to do.  Script cannot continue.\n";
      exit(1);
   }
   else
   {
     echo "Files in working directory (unsorted, unfiltered, " 
          . 
          count($file_list)
          . 
          " files):\n";
     for ($i = 0; $i < count($file_list); $i++)
        echo "   " . sprintf("[%5d]", $i) . " " . $file_list[$i] . "\n";
   }
   hor_line_thin();
   //-----------------------------------------------------------------------------
   //Figure out which file names are valid for .JPG files and create a
   //list containing only those.
   $found = FALSE;
   for ($i = 0; $i < count($file_list); $i++)
   {
      if (is_valid_jpg_file_name($file_list[$i]))
      {
         $found = TRUE;
         $staging_list[] = $file_list[$i];
      }   
   }
   
   if (!$found)
   {
      echo "There were no filenames corresponding to JPEG files.\n";
      echo "Script cannot continue.\n";
      exit(1);
   }

   $file_list = $staging_list;
   unset($staging_list);
   //-----------------------------------------------------------------------------
   //Sort the filenames, and provide the user with a list.
   sort($file_list, SORT_STRING);
   echo "JPEG file to be indexed (filtered, sorted, " 
        . 
        count($file_list)
        .
        " files):\n";
   for ($i = 0; $i < count($file_list); $i++)
      echo "   " . sprintf("[%5d]", $i) . " " . $file_list[$i] . "\n";
   hor_line_thin();
   //-----------------------------------------------------------------------------
   //Create a parallel list that contains the proposed names of files with new
   //names that are all lower-case.  If the lower-casing option is turned off,
   //just create a parallel identical list.
   for ($i = 0; $i < count($file_list); $i++)
   {
      if (CFG_IMAGE_LC_CONVERT)
         $file_list_lc[$i] = strtolower($file_list[$i]);
      else
         $file_list_lc[$i] = $file_list[$i];
   }
   //-----------------------------------------------------------------------------
   //Look for collisions between the two lists, and abort if there are collisions.
   //A collision essentially means that at least one file is differentiated from
   //at least one other file based only on case.  This kind of lazy comparison
   //is quadratic, but with 10,000 files it would involve about 10,000,000
   //comparisons--not too bad.  But for any serious computing, this couldn't be
   //done that way it is.
   $collisions = 0;
   for ($i = 0; $i < count($file_list); $i++)
   {
      for ($j = 0; $j < count($file_list); $j++)
      {
         if (($i != $j) && (strcmp($file_list[$i], $file_list_lc[$j]) == 0))
            $collisions++;
      }
   }

   if ($collisions != 0)
   {
      echo "There are filename collisions that have resulted from filenames\n";
      echo "differing only in case.  The script cannot continue.\n";
      exit(1);
   }
   //-----------------------------------------------------------------------------
   //Convert any filenames that need it to lower case.
   if (CFG_IMAGE_LC_CONVERT)
   {
      for ($i = 0; $i < count($file_list); $i++)
      {
         if (strcmp($file_list[$i], $file_list_lc[$i]) == 0)
         {
            echo "Skipped rename of \"" . $file_list[$i] .
                 "\" to lower case.\n";
         }
         else
         {
            $result = rename($file_list[$i], $file_list_lc[$i]);
            if ($result === TRUE)
            {
               echo "Renamed \""
               .
               $file_list[$i]
               .
               "\" to \""
               .
               $file_list_lc[$i]
               .
               "\".\n";       
            }
            else
            {
               echo "Rename of \""
               .
               $file_list[$i]
               .
               "\" to \""
               .
               $file_list_lc[$i]
               .
               "\" failed.\n";       
               echo "The script cannot continue.\n";
               exit(1);
            }
         }
      }

   hor_line_thin();
   }
   //-----------------------------------------------------------------------------
   //At this point, the lower-case list can be discarded.
   //-----------------------------------------------------------------------------
   $file_list = $file_list_lc;
   unset($file_list_lc);
   //-----------------------------------------------------------------------------
   //Create a parallel list of thumbnail file names.
   for ($i = 0; $i < count($file_list); $i++)
   {
      $thumbnail_list[$i] = file_name_to_thumbnail_name($file_list[$i]);
      //echo $thumbnail_list[$i] . "\n";
   }
   //-----------------------------------------------------------------------------
   //Check for duplicates.  A duplicate might occur, for example, if "x.jpg"
   //and "x_small.jpg" both exist.
   $collisions = 0;
   for ($i = 0; $i < count($file_list); $i++)
   {
      for ($j = 0; $j < count($thumbnail_list); $j++)
      {
         if (($i != $j) && (strcmp($file_list[$i], $file_list_lc[$j]) == 0))
            $collisions++;
      }
   }

   if ($collisions != 0)
   {
      echo "There are filename collisions that have resulted when trying\n";
      echo "to find thumbnail names.  Very likely some thumbnails already\n";
      echo "exist.  The script cannot continue.\n";
      exit(1);
   }
   //-----------------------------------------------------------------------------
   //Open up the index file for writing.  Abort script if unsuccessful.
   $index_handle = fopen(index_file_name(), "w");
   if ($index_handle === FALSE)
   {
      echo "Failed to open \"" . index_file_name() . "\" for writing.\nScript cannot continue.\n";
      exit(1);
   }
   else
   {
      echo "Successfully opened \"" . index_file_name() . "\" for writing.\n";
      hor_line_thin();
   }
   //-----------------------------------------------------------------------------
   //Write the index file preamble to the index file.  The preamble is everything
   //up until the lines that reference the thumbnails.
   write_index_file_preamble($index_handle);
   //-----------------------------------------------------------------------------
   //For each file, create the thumbnail and write the line in the index file.
   for ($i = 0; $i < count($file_list); $i++)
   {
      echo "Creating thumbnail \"" .
           $thumbnail_list[$i] .
           "\" from image \"" .
           $file_list[$i] .
           "\".\n";
      create_thumbnail($file_list[$i], 
                       $thumbnail_list[$i],
                       $filename_filesize,
                       $filename_xdim,
                       $filename_ydim,
                       $thumbnail_filesize,
                       $thumbnail_xdim,
                       $thumbnail_ydim);
      echo "Conversion complete.\n";
      echo "   Full-sized image file size/xdim/ydim = " .
           $filename_filesize . "/" . $filename_xdim . "/" . $filename_ydim .
           ",\n";
      echo "   Thumbnail image  filesize/xdim/ydim = " .
           $thumbnail_filesize . "/" . $thumbnail_xdim . "/" . $thumbnail_ydim .
           ",\n";
      write_index_line($index_handle,
                       $file_list[$i], 
                       $thumbnail_list[$i],
                       $filename_filesize,
                       $filename_xdim,
                       $filename_ydim,
                       $thumbnail_filesize,
                       $thumbnail_xdim,
                       $thumbnail_ydim);
      hor_line_thin();
   }
   //-----------------------------------------------------------------------------
   //Write the index file postamble to the index file.  The postamble is 
   //everything after the lines that reference the thumbnails.
   write_index_file_postamble($index_handle);
   //-----------------------------------------------------------------------------
   //Close the index file, not checking for error codes.
   fclose($index_handle);
   //-----------------------------------------------------------------------------
   echo "Execution ends.\n";
   hor_line_thick();
//--------------------------------------------------------------------------------
//End of File
//--------------------------------------------------------------------------------
?>