title: Convert Bitmap Files into JPEG using the GD library in PHP
body: <p>I have been trying to figure out a way to convert bitmap files into a JPEG using the GD library in PHP.</p>
  
  <p>I have tried numerous implementations but nothing seems to work.  I have tried to tell my client that they should not use Bitmap files but he insists and quite frankly does not comprehend enough about computers to convert them to JPG on his own.</p>
  
  <p>I can not use ImageMagick on this server and I need a pure GD solution.  Thank you in advance for any and all help.</p>
  
  <p><strong>EDIT:</strong></p>
  
  <p>The bitmap images that are being used are 16-bit and that is where the problem is occurring.</p>
  
  <p>I have this function that I have working .... kinda:</p>
  
  <pre><code>function ImageCreateFromBMP($filename) {
      if (! $f1 = fopen($filename,"rb")) return FALSE;
  
      $FILE = unpack("vfile_type/Vfile_size/Vreserved/Vbitmap_offset", fread($f1,14));
      if ($FILE['file_type'] != 19778) return FALSE;
  
      $BMP = unpack('Vheader_size/Vwidth/Vheight/vplanes/vbits_per_pixel'.
          '/Vcompression/Vsize_bitmap/Vhoriz_resolution'.
          '/Vvert_resolution/Vcolors_used/Vcolors_important', fread($f1,40));
      $BMP['colors'] = pow(2,$BMP['bits_per_pixel']);
  
      if ($BMP['size_bitmap'] == 0) $BMP['size_bitmap'] = $FILE['file_size'] - $FILE['bitmap_offset'];
      $BMP['bytes_per_pixel'] = $BMP['bits_per_pixel']/8;
      $BMP['bytes_per_pixel2'] = ceil($BMP['bytes_per_pixel']);
      $BMP['decal'] = ($BMP['width']*$BMP['bytes_per_pixel']/4);
      $BMP['decal'] -= floor($BMP['width']*$BMP['bytes_per_pixel']/4);
      $BMP['decal'] = 4-(4*$BMP['decal']);
      if ($BMP['decal'] == 4) $BMP['decal'] = 0;
  
      $PALETTE = array();
      if ($BMP['colors'] &lt; 16777216 &amp;&amp; $BMP['colors'] != 65536) {
          $PALETTE = unpack('V'.$BMP['colors'], fread($f1,$BMP['colors']*4));
      }
  
      $IMG = fread($f1,$BMP['size_bitmap']);
      $VIDE = chr(0);
  
      $res = imagecreatetruecolor($BMP['width'],$BMP['height']);
      $P = 0;
      $Y = $BMP['height']-1;
      while ($Y &gt;= 0) {
          $X=0;
          while ($X &lt; $BMP['width']) {
              if ($BMP['bits_per_pixel'] == 24)
                  $COLOR = unpack("V",substr($IMG,$P,3).$VIDE);
              elseif ($BMP['bits_per_pixel'] == 16) {
                  $COLOR = unpack("v",substr($IMG,$P,2));
                  $blue  = ($COLOR[1] &amp; 0x001f) &lt;&lt; 3;
                  $green = ($COLOR[1] &amp; 0x07e0) &gt;&gt; 3;
                  $red   = ($COLOR[1] &amp; 0xf800) &gt;&gt; 8;
                  $COLOR[1] = $red * 65536 + $green * 256 + $blue;
              }
              elseif ($BMP['bits_per_pixel'] == 8) {
                  $COLOR = unpack("n",$VIDE.substr($IMG,$P,1));
                  $COLOR[1] = $PALETTE[$COLOR[1]+1];
              }
              elseif ($BMP['bits_per_pixel'] == 4) {
                  $COLOR = unpack("n",$VIDE.substr($IMG,floor($P),1));
                  if (($P*2)%2 == 0) $COLOR[1] = ($COLOR[1] &gt;&gt; 4) ; else $COLOR[1] = ($COLOR[1] &amp; 0x0F);
                  $COLOR[1] = $PALETTE[$COLOR[1]+1];
              }
              elseif ($BMP['bits_per_pixel'] == 1) {
                  $COLOR = unpack("n",$VIDE.substr($IMG,floor($P),1));
                  if     (($P*8)%8 == 0) $COLOR[1] =  $COLOR[1]        &gt;&gt;7;
                  elseif (($P*8)%8 == 1) $COLOR[1] = ($COLOR[1] &amp; 0x40)&gt;&gt;6;
                  elseif (($P*8)%8 == 2) $COLOR[1] = ($COLOR[1] &amp; 0x20)&gt;&gt;5;
                  elseif (($P*8)%8 == 3) $COLOR[1] = ($COLOR[1] &amp; 0x10)&gt;&gt;4;
                  elseif (($P*8)%8 == 4) $COLOR[1] = ($COLOR[1] &amp; 0x8)&gt;&gt;3;
                  elseif (($P*8)%8 == 5) $COLOR[1] = ($COLOR[1] &amp; 0x4)&gt;&gt;2;
                  elseif (($P*8)%8 == 6) $COLOR[1] = ($COLOR[1] &amp; 0x2)&gt;&gt;1;
                  elseif (($P*8)%8 == 7) $COLOR[1] = ($COLOR[1] &amp; 0x1);
                  $COLOR[1] = $PALETTE[$COLOR[1]+1];
              }
              else
                  return FALSE;
  
              imagesetpixel($res,$X,$Y,$COLOR[1]);
  
              $X++;
              $P += $BMP['bytes_per_pixel'];
          }
          $Y--;
          $P+=$BMP['decal'];
      }
  
      fclose($f1);
      return $res;
  }
  </code></pre>
  
  <p>The resulting image is this:</p>
  
  <p><img src="https://i.stack.imgur.com/4RcOI.jpg" alt="Uploaded Image"></p>
  
  <p>If you look at the image on the left hand side you can see that the resulting image is not correctly lined up.  The little sliver belongs on the right hand side.  Where is the code going wrong?  The problem is occurring in the 16-bit else-if.</p>
  
  <p>Thank you again for all the help.</p>