更改图像的尺寸但仅声明宽度

Question

I have this code:

<?php
// The file
$filename = 'http://www.tagesschau.de/multimedia/bilder/feinstaub-messstation-101.jpg';
$new_width = 400;
$new_height = 200;

// Content type
header('Content-type: image/jpeg');

// Get new dimensions
list($width, $height) = getimagesize($filename);

// Resample
$image_p = imagecreatetruecolor($new_width, $new_height);
$image = imagecreatefromjpeg($filename);
imagecopyresampled($image_p, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height);

// Output
imagejpeg($image_p, null, 100);
?>

When calling this script it'll show the image http://www.tagesschau.de/multimedia/bilder/feinstaub-messstation-101.jpg but resize the image before: 400 x 200.

You can declare width and height with the values in $new_width and $new_height. I need to specify width and height.

What I want to reach: I want to only declare width. Height should adapt dynamically proportional to the original dimensions. Is there a way to do this?

Answer 1

Get the ratio of new to original width, then apply that factor to height:

$factor = $new_width / $width;
$new_height = $height * $factor;