MrFreeman555 MrFreeman555 - 22 days ago 6
PHP Question

Convert JPEG to 8bit BMP

I've code which convert into 16bit bmp; I was trying to find out what should be change or add to achive 8 bit bmp file but still nothing. I can only imagine that should be change $bfOffBits

<?php
//convert jpeg to 16 bit bmp

$jpgImageFile = 'TEST.jpg';
$newFileName = 'NEW_BMP';


$imageSource = imagecreatefromjpeg($jpgImageFile);
imagebmp($imageSource,$newFileName.".bmp");


function imagebmp(&$im, $filename = "")
{
if (!$im) return false;
$w = imagesx($im);
$h = imagesy($im);
$result = '';

if (!imageistruecolor($im)) {
$tmp = imagecreatetruecolor($w, $h);
imagecopy($tmp, $im, 0, 0, 0, 0, $w, $h);
imagedestroy($im);
$im = & $tmp;
}

$biBPLine = $w * 2;
$biStride = ($biBPLine + 3) & ~3;
$biSizeImage = $biStride * $h;
$bfOffBits = 66;
$bfSize = $bfOffBits + $biSizeImage;
$result .= substr('BM', 0, 2);
$result .= pack ('VvvV', $bfSize, 0, 0, $bfOffBits);
$result .= pack ('VVVvvVVVVVV', 40, $w, '-'.$h, 1, 16, 3, $biSizeImage, 0, 0, 0, 0);
$numpad = $biStride - $biBPLine;


$result .= pack('VVV',63488,2016,31);
for ($y = 0; $y < $h; ++$y) {
for ($x = 0; $x < $w; ++$x) {

$rgb = imagecolorat($im, $x, $y);
$r24 = ($rgb >> 16) & 0xFF;
$g24 = ($rgb >> 8) & 0xFF;
$b24 = $rgb & 0xFF;
$col = ((($r24 >> 3) << 11) | (($g24 >> 2) << 5) | ($b24 >> 3));
$result .= pack('v',$col);
}
for ($i = 0; $i < $numpad; ++$i)
$result .= pack ('C', 0);
}
if($filename==""){
}
else
{
$file = fopen($filename, "wb");
fwrite($file, $result);
fclose($file);
}
return true;
}
?>


Question: How it looks like for 8bit?

Answer

I hope that I found the answer. I've used imagick library becouse GD library doesn't respond bmp format, instead it uses wbmp which makes a diffrence.

My code to call imagick:

<?php
//convert jpeg to 8 bit bmp with imagick library

//Read the image
$im = new imagick( 'input.jpg' );

// Set number of colors
$numberColors = 256;

// Set colorspace
$colorSpace = Imagick::COLORSPACE_SRGB;

// Set tree depth
$treeDepth = 0;

// Set dither
$dither = false;

// Set quanitize
$im->quantizeImage($numberColors, $colorSpace, $treeDepth, $dither, false);

// write to disk
$im->writeImage( 'output.bmp' );
?>
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