Explication détaillée de la façon dont PHP convertit les images en stockage TXT

<?php
// 打开一幅图像
$file_name=&#39;d:\ascii_dora.png&#39;;
$chars = "$@B%8&WM#*oahkbdpqwmZO0QLCJUYXzcvunxrjft/\|()1{}[]?-_+~<>i!lI;:,\"^`&#39;. ";
function getimgchars($color_tran,$chars){
  $length = strlen($chars);
  $alpha=$color_tran[&#39;alpha&#39;];
  $r=$color_tran[&#39;red&#39;];
  $g=$color_tran[&#39;green&#39;];
  $b=$color_tran[&#39;blue&#39;];
  $gray = intval(0.2126 * $r + 0.7152 * $g + 0.0722 * $b);
  if($gray==0){
    return &#39;.&#39;;
  }
  if($gray<196){
     $unit = (256.0 + 1)/$length;
    return $chars[intval($gray/$unit)];
  }
  return " ";
}

function color_img($color_tran,$chars){
  $length = strlen($chars);
  $alpha=$color_tran[&#39;alpha&#39;];
  $r=$color_tran[&#39;red&#39;];
  $g=$color_tran[&#39;green&#39;];
  $b=$color_tran[&#39;blue&#39;];
  $gray = intval(0.2126 * $r + 0.7152 * $g + 0.0722 * $b);
  $rand=rand (0, $length-1);
  $color="rgb(".$r.",".$g.",".$b.")";
  $char=$chars[$rand];
  return &#39;<span style="color:&#39;.$color.&#39;" >&#39;.$char."</span>";;
}

function resize_img($file_name,$chars,$flage=true){
  //header(&#39;Content-Type: image/jpeg&#39;);
  list($width, $height,$type) = getimagesize($file_name);
  $fun=&#39;imagecreatefrom&#39; . image_type_to_extension($type, false);
  if($type==3){
    $flage=false;
  }
  $fun($file_name);
  $new_height =100;
  $percent=$height/$new_height;
  $new_width=$width/$percent;
  $image_p = imagecreatetruecolor($new_width, $new_height);
  $image = $fun($file_name);
  imagecopyresampled($image_p, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height);
  if($flage){
    return $image_p;
  }else{
    return $image;
  }
}

$im=resize_img($file_name,$chars);
$width=imagesx($im);
$height=imagesy($im);
$back_text="";

for($i=1;$i<=$height;$i++){
  for($j=1;$j<=$width;$j++){
    $color_index = imagecolorat($im, $j-1, $i-1);
    $color_tran = imagecolorsforindex($im, $color_index);
    $back_text.=color_img($color_tran,$chars,false);
  }
  $back_text.="<br/>";
}
 
echo "<pre class="brush:php;toolbar:false">";
echo $back_text;
echo "