How to use GD to manipulate images in php

This article mainly introduces the method of using GD in PHP to create thumbnails that maintain the aspect ratio. It involves the skills of PHP using the GD library to operate images. Friends in need can refer to the following.

The examples in this article describe the use of PHP GD's way of creating thumbnails that maintain aspect ratio. The details are as follows:

/**
* Create a thumbnail image from $inputFileName no taller or wider than
* $maxSize. Returns the new image resource or false on error.
* Author: mthorn.net
*/
function thumbnail($inputFileName, $maxSize = 100)
{
 $info = getimagesize($inputFileName);
  $type = isset($info['type']) ? $info['type'] : $info[2];
  // Check support of file type
 if ( !(imagetypes() & $type) )
 {
   // Server does not support file type
   return false;
 }
  $width = isset($info['width']) ? $info['width'] : $info[0];
 $height = isset($info['height']) ? $info['height'] : $info[1];
  // Calculate aspect ratio
 $wRatio = $maxSize / $width;
 $hRatio = $maxSize / $height;
  // Using imagecreatefromstring will automatically detect the file type
 $sourceImage = imagecreatefromstring(file_get_contents($inputFileName));
  // Calculate a proportional width and height no larger than the max size.
 if ( ($width <= $maxSize) && ($height <= $maxSize) )
 {
   // Input is smaller than thumbnail, do nothing
   return $sourceImage;
 }
 elseif ( ($wRatio * $height) < $maxSize )
 {
   // Image is horizontal
   $tHeight = ceil($wRatio * $height);
   $tWidth = $maxSize;
 }
 else
 {
   // Image is vertical
   $tWidth = ceil($hRatio * $width);
   $tHeight = $maxSize;
 }
  $thumb = imagecreatetruecolor($tWidth, $tHeight);
  if ( $sourceImage === false )
 {
   // Could not load image
   return false;
 }
  // Copy resampled makes a smooth thumbnail
 imagecopyresampled($thumb,$sourceImage,0,0,0,0,$tWidth,$tHeight,$width,$height);
 imagedestroy($sourceImage);
  return $thumb;
}
 /**
* Save the image to a file. Type is determined from the extension.
* $quality is only used for jpegs.
* Author: mthorn.net
*/
function imageToFile($im, $fileName, $quality = 80)
{
 if ( !$im || file_exists($fileName) )
 {
   return false;
 }
  $ext = strtolower(substr($fileName, strrpos($fileName, &#39;.&#39;)));
  switch ( $ext )
 {
  case &#39;.gif&#39;:
  imagegif($im, $fileName);
  break;
  case &#39;.jpg&#39;:
  case &#39;.jpeg&#39;:
  imagejpeg($im, $fileName, $quality);
  break;
  case &#39;.png&#39;:
  imagepng($im, $fileName);
  break;
  case &#39;.bmp&#39;:
  imagewbmp($im, $fileName);
  break;
  default:
  return false;
 }
  return true;
}
$im = thumbnail(&#39;temp.jpg&#39;, 100);
imageToFile($im, &#39;temp-thumbnail.jpg&#39;);

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