Getting proportionally-resized dimensions of an image

Heads up! This post was written in 2007, so it may contain information that is no longer accurate. I keep posts like this around for historical purposes and to prevent link rot, so please keep this in mind as you're reading.

— Cory

This is extremely useful when you need to scale down an image within a certain pair of dimensions.

get_resized_dimensions() #

Parameters #

• $width - The width of the image to be resized
• $height - The height of the image to be resized
• $max_width - The maximum allowed width of the resized image
• $max_height - The maximum allowed height of the resized image

Return values #

The function outputs an array containing two elements: width and height

$new_dimensions = get_resized_dimensions(640, 480, 200, 200)
echo $new_dimensions['width'] . ', ' . $new_dimensions['height'];

The output for the above code will be: 200, 150

Code #

function get_resized_dimensions($width, $height, $max_width, $max_height) {
  // Check for bad values
  if ($width <= 0 || $height <= 0) return false;

  // Determine aspect ratio
  $aspect_ratio = $height / $width;

  // First check width
  if ($width > $max_width) {
    $new_width = $max_width;
    $new_height = $new_width * $aspect_ratio;
  } else {
    $new_width = $width;
    $new_height = $height;
  }

  // Now check height
  if ($new_height > $max_height) {
    $new_height = $max_height;
    $new_width = $new_height / $aspect_ratio;
  }

  return array('width' => $new_width, 'height' => $new_height);
}