Error showing image with GD

Question

I’m trying to display a PNG image on the client’s browser screen using PHP, but only a black screen with a comic in the center appears.

What am I doing wrong? Here’s my code:

<?php

        $file  = "img.png";
        $width = 500;
        $height= 500;

        list($width_origin,$height_origin) = getimagesize($file);
        $ratio = $width_origin / $height_origin;

        if ($width/$height > $ratio) {
            $width = $height * $ratio;
        }else{
            $height = $width / $ratio;
        }

        $image_final  = imagecreatetruecolor($width, $height);
        $imagem_origin= imagecreatefrompng($file);
        imagecopyresampled($image_final,$imagem_origin,0,0,0,0,$width,$height,$width_origin,$height_origin);
        header("Content-type: image/png");
        imagepng($image_final,"imagem_nova.png");


    ?>

Answer 1

If you put the second parameter in imagepng it will not display but save, as described in the documentation http://php.net/manual/en/function.imagepng.php

If not set or NULL, the raw image stream will be outputted directly.

That is if the second parameter is not defined or is NULL it will display, otherwise it will save to a file.

So whenever you have questions, do a search in the documentation and read how to use each parameter and see the examples. In case your code should look like this:

<?php

$file  = "img.png";
$width = 500;
$height= 500;

list($width_origin, $height_origin) = getimagesize($file);

$ratio = $width_origin / $height_origin;

if ($width/$height > $ratio) {
    $width = $height * $ratio;
}else{
    $height = $width / $ratio;
}

$image_final  = imagecreatetruecolor($width, $height);
$imagem_origin= imagecreatefrompng($file);
imagecopyresampled($image_final,$imagem_origin, 0, 0, 0, 0, $width, $height, $width_origin, $height_origin);
header("Content-Type: image/png");

imagepng($image_final); //Exibe a imagem

If you want to view and save at the same time, you can use various methods, such as saving to a stream or file directly:

• Using readfile:

  if (imagepng($image_final, $file)) //salva para um arquivo
  {
      header("Content-Type: image/png");
      readfile($file);
  } else {
      echo 'Erro ao salvar';
  }
  

• fopen+stream_get_contents

  This is a little more complicated, but if you need to do some manipulation in the stream it might be interesting to use it.

  $handle = fopen($handle, 'wb');
  
  if (!$handle) {
      die('Erro ao abrir o arquivo para escrita');
  }
  
  if (imagepng($image_final, $handle)) //salva para um arquivo
  {
      header("Content-Type: image/png");
      echo stream_get_contents($handle);
  } else {
      echo 'Erro ao salvar';
  }
  
  fclose($handle);
  

What each parameter does:

The function is basically

bool imagepng ( resource $image [, mixed $to [, int $quality [, int $filters ]]] )

• $image

  Must be a Resource of an image, returned by image creation functions, for example imagecreatetruecolor(), imagecreatefrompng(), etc..

• $to

  The path or an open stream (which will be automatically closed when the function returns) to save the file. If not set or is NULL, the image will be displayed in the output.

• $quality

  Compaction level: if 0 (no compaction) up to 9.

• $filters

  Allows you to reduce the size of the PNG file. This is a bitmask which may define any combination of constant PNG_FILTER_XXX. Use PNG_NO_FILTER or PNG_ALL_FILTERS or using them respectively will disable or enable all filters.