I'm having some issues putting 2 pieces of code together

First part
I have this string
$string = "some text... <img src=myimage.jpg> some more text <img src=myimage.jpg>";

What i want to do is add width and height to those img tags and automatically reduce the image size by like 50%. I have a function that returns the image width and height in an array. For example

$resized_image = imgresize("path to image");
I then can print $resized_image[height] to get the height, and $resized_image[width] for the width.

Second part
I have a reg exp that will search for the image tag and add width and height

$pattern = "/(<img\s+).*?src=((\".*?\")|(\'.*?\')|([^\s]*)).*?>/is";
$replacement = "<img src=$2 width=$resized_image[width] height=$resized_image[height]>";

echo preg_replace($pattern, $replacement, $string);
How can i tie these 2 together? The only way i can think of is to call the array in the $replacement string, but dont know how to do so with an array