日志

Convert BMP to JPG

已有 1259 次阅读2009-3-26 21:44 |个人分类:PHP|

The PHP GD library contains many wonderful tools for creating images and converting them. Sadly the ability to convert BMP images to JPG is not one of them. Here is a function that I find a little slow, but works well and has suffered several incarnations.

<?php

/**
*
* @convert BMP to GD
*
* @param string $src
*
* @param string|bool $dest
*
* @return bool
*
*/
function bmp2gd($src, $dest = false)
{
    /*** try to open the file for reading ***/
    if(!($src_f = fopen($src, "rb")))
    {
        return false;
    }

/*** try to open the destination file for writing ***/
if(!($dest_f = fopen($dest, "wb")))
    {
        return false;
    }

/*** grab the header ***/
$header = unpack("vtype/Vsize/v2reserved/Voffset", fread( $src_f, 14));

/*** grab the rest of the image ***/
$info = unpack("Vsize/Vwidth/Vheight/vplanes/vbits/Vcompression/Vimagesize/Vxres/Vyres/Vncolor/Vimportant",
fread($src_f, 40));

/*** extract the header and info into varibles ***/
extract($info);
extract($header);

/*** check for BMP signature ***/
if($type != 0x4D42)
{
    return false;
}

/*** set the pallete ***/
$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);
}
/*** we do not allow transparency ***/
$gd_header .= "\xFF\xFF\xFF\xFF";

/*** write the destination headers ***/
fwrite($dest_f, $gd_header);

/*** if we have a valid palette ***/
if($palette_size)
{
    /*** read the palette ***/
    $palette = fread($src_f, $palette_size);
    /*** begin the gd palette ***/
    $gd_palette = "";
    $j = 0;
    /*** loop of the palette ***/
    while($j < $palette_size)
    {
        $b = $palette{$j++};
        $g = $palette{$j++};
        $r = $palette{$j++};
        $a = $palette{$j++};
        /*** assemble the gd palette ***/
        $gd_palette .= "$r$g$b$a";
    }
    /*** finish the palette ***/
    $gd_palette .= str_repeat("\x00\x00\x00\x00", 256 - $ncolor);
    /*** write the gd palette ***/
    fwrite($dest_f, $gd_palette);
}

/*** scan line size and alignment ***/
$scan_line_size = (($bits * $width) + 7) >> 3;
$scan_line_align = ($scan_line_size & 0x03) ? 4 - ($scan_line_size & 0x03) : 0;

/*** this is where the work is done ***/
for($i = 0, $l = $height - 1; $i < $height; $i++, $l--)
{
    /*** create scan lines starting from bottom ***/
    fseek($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++};
            $gd_scan_line .= "\x00$r$g$b";
        }
    }
    elseif($bits == 8)
    {
        $gd_scan_line = $scan_line;
    }
    elseif($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, $width);
    }
    elseif($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";
        }
    /*** put the gd scan lines together ***/
    $gd_scan_line = substr($gd_scan_line, 0, $width);
    }
    /*** write the gd scan lines ***/
    fwrite($dest_f, $gd_scan_line);
}
/*** close the source file ***/
fclose($src_f);
/*** close the destination file ***/
fclose($dest_f);

return true;
}

/**
*
* @ceate a BMP image
*
* @param string $filename
*
* @return bin string on success
*
* @return bool false on failure
*
*/
function ImageCreateFromBmp($filename)
{
    /*** create a temp file ***/
    $tmp_name = tempnam("/tmp", "GD");
    /*** convert to gd ***/
    if(bmp2gd($filename, $tmp_name))
    {
        /*** create new image ***/
        $img = imagecreatefromgd($tmp_name);
        /*** remove temp file ***/
        unlink($tmp_name);
        /*** return the image ***/
        return $img;
    }
    return false;
}

/*** example usage ***/

/*** read in the BMP image ***/
$img = ImageCreateFromBmp("test.bmp");
/*** write the new jpeg image ***/
imagejpeg($img, "test/test.jpg");

?>


<img src="test/test.jpg" alt="new jpg image" />