使用gzinflate嘗試,但跳過第2個字節和最後4首。
$contents = file_get_contents($in_filename);
$pos = 8; // skip header
$color_types = array('Greyscale','unknown','Truecolour','Indexed-color','Greyscale with alpha','unknown','Truecolor with alpha');
$len = strlen($contents);
$safety = 1000;
do {
list($unused,$chunk_len) = unpack('N', substr($contents,$pos,4));
$chunk_type = substr($contents,$pos+4,4);
$chunk_data = substr($contents,$pos+8,$chunk_len);
list($unused,$chunk_crc) = unpack('N', substr($contents,$pos+8+$chunk_len,4));
echo "chunk length:$chunk_len(dec) 0x" . sprintf('%08x',$chunk_len) . "h<br>\n";
echo "chunk crc :0x" . sprintf('%08x',$chunk_crc) . "h<br>\n";
echo "chunk type :$chunk_type<br>\n";
echo "chunk data $chunk_type bytes:<br>\n" . chunk_split(bin2hex($chunk_data)) . "<br>\n";
switch($chunk_type) {
case 'IHDR':
list($unused,$width,$height) = unpack('N2', substr($chunk_data,0,8));
list($unused,$depth,$Color_type,$Compression_method,$Filter_method,$Interlace_method) = unpack('C*', substr($chunk_data,8));
echo "Width:$width,Height:$height,depth:$depth,Color_type:$Color_type(" . $color_types[$Color_type] . "),Compression_method:$Compression_method,Filter_method:$Filter_method,Interlace_method:$Interlace_method<br>\n";
$bytes_per_pixel = $depth/8;
break;
case 'PLTE':
$palette = array();
for($i=0;$i<$chunk_len;$i+=3) {
$tupl = bin2hex(substr($chunk_data,$i,3));
$palette[] = $tupl;
if($i && ($i % 30 == 0)) {
echo "<br>\n";
}
echo '<span style="color:' . $tupl . ';">[' . $tupl . ']</span>';
}
echo print_r($palette,true) . "<br>";
break;
case 'IDAT':
$compressed = substr($chunk_data,2,$chunk_len - 6); // 2 bytes on the front and 4 at the end
$decompressed = gzinflate($compressed);
echo "decompressed chunk data " . strlen($decompressed) . " bytes:<br>\n" . chunk_split(bin2hex($decompressed),2 + $width * $bytes_per_pixel * 2) . "<br>\n";
for($row=0; $row<$height; $row++) {
for($col=1; $col<=$width; $col++) {
$index = (int)substr($decompressed,((int)$row*($width+1)+$col),1);
echo '<span style="color:' . $palette[$index] . ';">' . $index . '</span>';
}
echo "<br>\n";
}
// TODO use filters described here:
// http://www.w3.org/TR/PNG/#9Filters
// first byte of scan line is filter type
break;
}
$pos += $chunk_len + 12;
echo "<hr>";
} while(($pos < $len) && --$safety);
謝謝,現在膨脹工作,但我得到「00000000ffffff00ffffff000000 「(14個字節),它們如何用於獲取像素? – MatTheCat
爲了獲得良好的壓縮效果,PNG格式在壓縮之前應用濾鏡。這些濾波器的作用如下:如果兩條掃描線彼此幾乎相同,則較低線上與上述像素相匹配的像素將變爲零。所以當你完成你有一個零碎的零和壓縮是非常好的。所以你需要反轉,並在解壓縮後撤銷過濾器。見http://www.w3.org/TR/PNG/#9過濾器 – Charlie
正確,過濾器「將掃描行中的字節序列轉換爲以過濾器類型字節開頭的等長字節序列」。所以我不應該有18個字節的未壓縮數據(1「字節深度」* 4通道* 4像素+ 2個濾波器)? – MatTheCat