[GD] Generate images in bmp format (imagebmp)

There is no function to generate bmp images in the GD library, so I wrote one myself. This function also has a compression algorithm that I haven't written yet, but it is enough. Students who need it can take a look.

int imagebmp (resource image [, string filename [, int $bit [, int compression]]] )

$im: image resource
$filename: If you want to save as a file, please specify the file name. If it is empty, it will be output directly in the browser.
$bit: image quality (1, 4, 8, 16, 24, 32 bits)
$compression: compression method, 0 means no compression, 1 uses RLE8 compression algorithm for compression.

Note: This function still requires the support of the GD library.

Demo:

$im = imagecreatefrompng("test.png");
imagebmp($im);
imagedestroy($im);
Source:

/**
* Create bmp format pictures
*
* @author: legend( [email protected] )
* @link: http://www.ugia.cn/?p=96
* @description: create Bitmap-File with GD library
* @version: 0.1
*
* @param resource $im image resource
* @param string $filename If you want to save as a file, please specify the file name. If it is empty, it will be output directly in the browser.
* @param integer $bit image quality (1, 4, 8, 16, 24, 32 bits)
* @param integer $compression compression method, 0 means no compression, 1 uses RLE8 compression algorithm for compression
*
* @return integer
*/
function imagebmp(&$im, $filename = '', $bit = 8, $compression = 0)
{
if (!in_array($bit, array(1, 4, 8, 16, 24, 32)))
{
$bit = 8;
}
else if ($bit == 32) // todo:32 bit
{
$bit = 24;
}

$bits = pow(2, $bit);

//Adjust color palette
imagetruecolortopalette($im, true, $bits);
$width = imagesx($im);
$height = imagesy($im);
$colors_num = imagecolorstotal($im);

if ($bit <= 8)
{
// color index
$rgb_quad = '';
for ($i = 0; $i < $colors_num; $i ++)
{
$colors = imagecolorsforindex($im, $i);
$rgb_quad .= chr($colors['blue']) . chr($colors['green']) . chr($colors['red']) . "";
}

// bitmap data
$bmp_data = '';

// uncompressed
if ($compression == 0 || $bit < 8)
{
if (!in_array($bit, array(1, 4, 8)))
{
$bit = 8;
}

$compression = 0;

//The number of bytes in each line must be a multiple of 4 and must be completed.
$extra = '';
$padding = 4 - ceil($width / (8 / $bit)) % 4;
if ($padding % 4 != 0)
{
$extra = str_repeat("", $padding);
}

for ($j = $height - 1; $j >= 0; $j --)
{
$i = 0;
while ($i < $width)
{
$bin = 0;
$limit = $width - $i < 8 / $bit ? (8 / $bit - $width + $i) * $bit : 0;

for ($k = 8 - $bit; $k >= $limit; $k -= $bit)
{
$index = imagecolorat($im, $i, $j);
$bin |= $index << $k;
$i++;
}

$bmp_data .= chr($bin);
}

$bmp_data .= $extra;
}
}
// RLE8 compression
else if ($compression == 1 && $bit == 8)
{
for ($j = $height - 1; $j >= 0; $j --)
{
$last_index = "";
$same_num = 0;
for ($i = 0; $i <= $width; $i ++)
{
$index = imagecolorat($im, $i, $j);
if ($index !== $last_index || $same_num > 255)
{
if ($same_num != 0)
{
$bmp_data .= chr($same_num) . chr($last_index);
}

$last_index = $index;
$same_num = 1;
}
else
{
$same_num++;
}
}

$bmp_data .= "";
}

$bmp_data .= "1";
}

$size_quad = strlen($rgb_quad);
$size_data = strlen($bmp_data);
}
else
{
//The number of bytes in each line must be a multiple of 4 and must be completed.
$extra = '';
$padding = 4 - ($width * ($bit / 8)) % 4;
if ($padding % 4 != 0)
{
$extra = str_repeat("", $padding);
}

// bitmap data
$bmp_data = '';

for ($j = $height - 1; $j >= 0; $j --)
{
for ($i = 0; $i < $width; $i ++)
{
$index = imagecolorat($im, $i, $j);
$colors = imagecolorsforindex($im, $index);

if ($bit == 16)
{
$bin = 0 << $bit;

$bin |= ($colors['red'] >> 3) << 10;
$bin |= ($colors['green'] >> 3) << 5;
$bin |= $colors['blue'] >> 3;

$bmp_data .= pack("v", $bin);
}
else
{
$bmp_data .= pack("c*", $colors['blue'], $colors['green'], $colors['red']);
}

// todo: 32bit;
}

$bmp_data .= $extra;
}

$size_quad = 0;
$size_data = strlen($bmp_data);
$colors_num = 0;
}

// Bitmap file header
$file_header = "BM" . pack("V3", 54 + $size_quad + $size_data, 0, 54 + $size_quad);

// Bitmap information header
$info_header = pack("V3v2V*", 0x28, $width, $height, 1, $bit, $compression, $size_data, 0, 0, $colors_num, 0);

// write to file
if ($filename != '')
{
$fp = fopen("test.bmp", "wb");

fwrite($fp, $file_header);
fwrite($fp, $info_header);
fwrite($fp, $rgb_quad);
fwrite($fp, $bmp_data);
fclose($fp);

return 1;
}

//Browser output
header("Content-Type: image/bmp");
echo $file_header .$info_header;
echo $rgb_quad;
echo $bmp_data;

return 1;
}
Reference material: BMP file format analysis (source not found...)

Original article, please indicate the source when reprinting.

Source: http://www.ugia.cn/?p=96