Re: BMP to GD (then to JPG) - 32 bits?

From: Chung Leong (chernyshevsky_at_hotmail.com)
Date: 06/25/04

  • Next message: Matt: "Session variables in IE" 
    Date: Thu, 24 Jun 2004 20:45:19 -0400

    "Ken" <hanson_kenneth@yahoo.com> wrote in message
    news:ea8389b0.0406241003.151b8cea@posting.google.com...
    > I need to convert 32 bit Windows bitmaps to jpgs with PHP.
    >
    > I used the function from http://groups.google.com/groups?
    > hl=en&lr=&ie=UTF-8&oe=UTF-8&safe=off&selm=a164f4b5.0311302128.40fb37f4%
    > 40posting.google.com to convert bitmaps to jpgs.
    >
    > It works very well for my 24 bit bitmaps, but I cannot figure out how
    > to
    > get it to work with 32 bits. I tried adding an additional scan line
    > and
    > the image appears in the correct size, but the colors are way off and
    > some of the data is missing. I also tried putting $a in different
    > places within the $gd_scan_line string:
    >
    > This did not work:
    >
    > $b = $scan_line{$j++};
    > $g = $scan_line{$j++};
    > $r = $scan_line{$j++};
    > $a = $scan_line{$j++};
    > $gd_scan_line .= "\x$a$r$g$b";
    >
    > Can anyone help?
    >
    > Ken

    You were close. Should have been $gd_scan_line .= "$a$r$g$b". Actually, the
    GD library interprets the alpha value as transparency (255 = fully
    transparent) while Windows sees it as opacity (0 = fully transparent). So we
    actually need to substract $a from 255 to get the correct value.

    Here's the update code. Improved it a bit by avoiding the use of a temporary
    file.

    <?

    function ConvertBMP2GD($src, $dest = false) {
     if(!($src_f = fopen($src, "rb"))) {
      trigger_error("Can't open $src", E_WARNING);
      return false;
     }
     if(!($dest_f = fopen($dest, "wb"))) {
      trigger_error("Can't open $dest", E_WARNING);
      return false;
     }
     $header = unpack("vtype/Vsize/v2reserved/Voffset", fread($src_f, 14));
     $info =
    unpack("Vsize/Vwidth/Vheight/vplanes/vbits/Vcompression/Vimagesize/Vxres/Vyr
    es/Vncolor/Vimportant", fread($src_f, 40));

     extract($info);
     extract($header);

     if($type != 0x4D42) { // signature "BM"
      return false;
     }

     $palette_size = $offset - 54;
     $ncolor = $palette_size / 4;
     $gd_header = "";
     // true-color vs. palette
     $gd_header .= ($palette_size == 0) ? "\xFF\xFE" : "\xFF\xFF";
     $gd_header .= pack("n2", $width, $height);
     $gd_header .= ($palette_size == 0) ? "\x01" : "\x00";
     if($palette_size) {
      $gd_header .= pack("n", $ncolor);
     }
     // no transparency
     $gd_header .= "\xFF\xFF\xFF\xFF";

     fwrite($dest_f, $gd_header);

     if($palette_size) {
      $palette = fread($src_f, $palette_size);
      $gd_palette = "";
      $j = 0;
      while($j < $palette_size) {
       $b = $palette{$j++};
       $g = $palette{$j++};
       $r = $palette{$j++};
       $a = $palette{$j++};
       $gd_palette .= "$r$g$b$a";
      }
      $gd_palette .= str_repeat("\x00\x00\x00\x00", 256 - $ncolor);
      fwrite($dest_f, $gd_palette);
     }

     $scan_line_size = (($bits * $width) + 7) >> 3;
     $scan_line_align = ($scan_line_size & 0x03) ? 4 - ($scan_line_size & 0x03)
    : 0;

     for($i = 0, $l = $height - 1; $i < $height; $i++, $l--) {
      // BMP stores scan lines starting from bottom
      fseek($src_f, $offset + (($scan_line_size + $scan_line_align) * $l));
      $scan_line = fread($src_f, $scan_line_size);
      if($bits == 24) {
       $gd_scan_line = "";
       $j = 0;
       while($j < $scan_line_size) {
        $b = $scan_line{$j++};
        $g = $scan_line{$j++};
        $r = $scan_line{$j++};
        $gd_scan_line .= "\xFF$r$g$b";
       }
      }
      else if($bits == 32) {
       $gd_scan_line = "";
       $j = 0;
       while($j < $scan_line_size) {
        $b = $scan_line{$j++};
        $g = $scan_line{$j++};
        $r = $scan_line{$j++};
        $a = chr(255 - ord($scan_line{$j++}));
        $gd_scan_line .= "$a$r$g$b";
       }
      }
      else if($bits == 8) {
       $gd_scan_line = $scan_line;
      }
      else if($bits == 4) {
       $gd_scan_line = "";
       $j = 0;
       while($j < $scan_line_size) {
        $byte = ord($scan_line{$j++});
        $p1 = chr($byte >> 4);
        $p2 = chr($byte & 0x0F);
        $gd_scan_line .= "$p1$p2";
       } $gd_scan_line = substr($gd_scan_line, 0, $width);
      }
      else if($bits == 1) {
       $gd_scan_line = "";
       $j = 0;
       while($j < $scan_line_size) {
        $byte = ord($scan_line{$j++});
        $p1 = chr((int) (($byte & 0x80) != 0));
        $p2 = chr((int) (($byte & 0x40) != 0));
        $p3 = chr((int) (($byte & 0x20) != 0));
        $p4 = chr((int) (($byte & 0x10) != 0));
        $p5 = chr((int) (($byte & 0x08) != 0));
        $p6 = chr((int) (($byte & 0x04) != 0));
        $p7 = chr((int) (($byte & 0x02) != 0));
        $p8 = chr((int) (($byte & 0x01) != 0));
        $gd_scan_line .= "$p1$p2$p3$p4$p5$p6$p7$p8";
       } $gd_scan_line = substr($gd_scan_line, 0, $width);
      }

      fwrite($dest_f, $gd_scan_line);
     }
     fclose($src_f);
     fclose($dest_f);
     return true;
    }

    class MemoryStream {
        var $position;
        var $varname;
        var $buffer;

        function stream_open($path, $mode, $options, &$opened_path)
        {
            $url = parse_url($path);
            $this->varname = $url["host"];
            $this->position = 0;
            $this->buffer = @$GLOBALS[$this->varname];

            return true;
        }

        function stream_close()
        {
            $GLOBALS[$this->varname] = $this->buffer;
        }

        function stream_read($count)
        {
            $ret = substr($this->buffer, $this->position, $count);
            $this->position += strlen($ret);
            return $ret;
        }

        function stream_write($data)
        {
            $this->buffer .= $data;
            $this->position += strlen($data);
            return strlen($data);
        }

        function stream_tell()
        {
            return $this->position;
        }

        function stream_eof()
        {
            return $this->position >= strlen($this->buffer);
        }

        function stream_stat() {
            return array( 'size' => strlen($this->buffer) );
        }
    }

    function imagecreatefrombmp($filename) {
     // use a memory stream instead of a temp file
     // where possible
     if(function_exists('stream_wrapper_register')
     && stream_wrapper_register("mem", "MemoryStream")) {
      $tmp_name = "mem://GD_TMP_FILE";
     $del_tmp = false;
     }
     else {
     $tmp_name = tempnam("/tmp", "GD");
     $del_tmp = true;
     }
     if(ConvertBMP2GD($filename, $tmp_name)) {
      $img = imagecreatefromgd($tmp_name);
      if($del_tmp) {
     unlink($tmp_name);
      }
      return $img;
     } return false;
    }

    $img = imagecreatefrombmp("test32bit.bmp");
    imagealphablending($img, false);
    imagesavealpha($img, true);
    imagepng($img, "test.png");

    ?>
    <img src="test.png">

  • Next message: Matt: "Session variables in IE"

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