PHP implementation supports transparent png image scaling

This article mainly introduces the method of scaling png images in PHP (supporting transparent background). It can realize PHP's scaling function for png images and supports transparent background, which has certain reference value. I hope to be helpful.

The specific implementation method is as follows:

function smart_resize_image( $file, $width = 0, $height = 0, $proportional = false, $output = 'file', $delete_original = true, $use_linux_commands = false )
{
    if ( $height <= 0 && $width <= 0 ) {
      return false;
    }
    $info = getimagesize($file);
    $image = '';
    $final_width = 0;
    $final_height = 0;
    list($width_old, $height_old) = $info;
    if ($proportional) {
      if ($width == 0) $factor = $height/$height_old;
      elseif ($height == 0) $factor = $width/$width_old;
      else $factor = min ( $width / $width_old, $height / $height_old); 
      $final_width = round ($width_old * $factor);
      $final_height = round ($height_old * $factor);
    }
    else {    
      $final_width = ( $width <= 0 ) ? $width_old : $width;
      $final_height = ( $height <= 0 ) ? $height_old : $height;
    }
    switch ($info[2] ) {
      case IMAGETYPE_GIF:
        $image = imagecreatefromgif($file);
      break;
      case IMAGETYPE_JPEG:
        $image = imagecreatefromjpeg($file);
      break;
      case IMAGETYPE_PNG:
        $image = imagecreatefrompng($file);
      break;
      default:
        return false;
    }
    $image_resized = imagecreatetruecolor( $final_width, $final_height );
    if ( ($info[2] == IMAGETYPE_GIF) || ($info[2] == IMAGETYPE_PNG) ) {
      $trnprt_indx = imagecolortransparent($image);
      // If we have a specific transparent color
      if ($trnprt_indx >= 0) {
        // Get the original image's transparent color's RGB values
        $trnprt_color  = imagecolorsforindex($image, $trnprt_indx);
        // Allocate the same color in the new image resource
        $trnprt_indx  = imagecolorallocate($image_resized, $trnprt_color['red'], $trnprt_color['green'], $trnprt_color['blue']);
        // Completely fill the background of the new image with allocated color.
        imagefill($image_resized, 0, 0, $trnprt_indx);
        // Set the background color for new image to transparent
        imagecolortransparent($image_resized, $trnprt_indx);
      }
      // Always make a transparent background color for PNGs that don't have one allocated already
      elseif ($info[2] == IMAGETYPE_PNG) {
        // Turn off transparency blending (temporarily)
        imagealphablending($image_resized, false);
        // Create a new transparent color for image
        $color = imagecolorallocatealpha($image_resized, 0, 0, 0, 127);
        // Completely fill the background of the new image with allocated color.
        imagefill($image_resized, 0, 0, $color);
        // Restore transparency blending
        imagesavealpha($image_resized, true);
      }
    }
    imagecopyresampled($image_resized, $image, 0, 0, 0, 0, $final_width, $final_height, $width_old, $height_old);
    if ( $delete_original ) {
      if ( $use_linux_commands )
        exec('rm '.$file);
      else
        @unlink($file);
    }
    switch ( strtolower($output) ) {
      case 'browser':
        $mime = image_type_to_mime_type($info[2]);
        header("Content-type: $mime");
        $output = NULL;
      break;
      case 'file':
        $output = $file;
      break;
      case 'return':
        return $image_resized;
      break;
      default:
      break;
    }
    switch ($info[2] ) {
      case IMAGETYPE_GIF:
        imagegif($image_resized, $output);
      break;
      case IMAGETYPE_JPEG:
        imagejpeg($image_resized, $output);
      break;
      case IMAGETYPE_PNG:
        imagepng($image_resized, $output);
      break;
      default:
        return false;
    }
    return true;
}

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