imagescale

(PHP 5 >= 5.5.0, PHP 7)

imagescale — Scale an image using the given new width and height

imagescale ( resource $image , int $new_width [, int $new_height = -1 [, int $mode = IMG_BILINEAR_FIXED ]] ) : resource|false

imagescale() scales an image using the given interpolation algorithm.

Note:
Unlike many of other image functions, imagescale() does not modify the passed image; instead, a new image is returned.

image: An image resource, returned by one of the image creation functions, such as imagecreatetruecolor().
new_width: The width to scale the image to.
new_height: The height to scale the image to. If omitted or negative, the aspect ratio will be preserved.
mode: One of IMG_NEAREST_NEIGHBOUR, IMG_BILINEAR_FIXED, IMG_BICUBIC, IMG_BICUBIC_FIXED or anything else (will use two pass).

Note:
IMG_WEIGHTED4 is not yet supported.

Return the scaled image resource on success or FALSE on failure.

Php/docs/function.imagescale