#code to convert 32bit BMP (actually DIB) to 24bit
sub check_bmp
{
  $input = shift;
  $output = shift;

  open(INPUT,"<$input");
  binmode(INPUT);

  # now read in the header

  read(INPUT,$buff,54);

  # sig, filesize, reserved, dataoffset, size, width, height, planes, 
+bitcount, compression, imagesize
  # xpixelsM, ypixelsM , colorsused, colorsimportant
  ( $sig, $filesize, $reserved, $dataoffset, $size, $width, $height, $
+planes, $bitcount, $compression, 
    $imagesize, $xpixelsM, $ypixelsM , $colorsused, $colorsimportant )
+ = unpack($headertemplate,$buff);

  if ($bitcount != 32)
  {
    close(INPUT);
    rename($input,$output);
  }
  else # only rework if 32 bit
  {
    # print "\n\tProcessing $input to $output\n";
    open(OUTPUT,">$output");
    binmode(OUTPUT);

    $bitcount = 24;
    $compression = 0;
    $imagesize = int (($imagesize) * 0.75);
    $filesize = $imagesize + $dataoffset;

    @fields = ( $sig, $filesize, $reserved, $dataoffset, $size, $width
+, $height, $planes, $bitcount, $compression, 
      $imagesize, $xpixelsM, $ypixelsM , $colorsused, $colorsimportant
+ ); 

    $buff2 = pack($headertemplate,@fields);

    syswrite(OUTPUT,$buff2,54);

    $count = 0;
    # now rewrite the BMP, dropping the alpha channel
    until( eof(INPUT) )
    {
      read(INPUT, $pixel, 4);
      ($r, $g, $b, $a) = unpack($rgbapixeltemplate,$pixel);
      $rgbpixel = pack($rgbpixeltemplate, $r, $g, $b);
      # $rgbpixel = $r.$g.$b;
      syswrite(OUTPUT,$rgbpixel,3);
    }

    close(INPUT);
    close(OUTPUT);
    
    # remove the .dib file
    unlink($input);
  }
}
[download]