Benefits of imagecreate ?

[mdb]

Hey guys,
So on my forum I wanted to apply a grayscale filter to a few of my images. I did it using this method:

PHP Code:

$pic = imagecreatefrompng('images/spray.png'); imagefilter($pic, IMG_FILTER_GRAYSCALE); imagesavealpha($pic, true); imagepng($pic, 'images/spray_grayscale.png'); imagedestroy($pic);

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However I noticed anytime someone views this page where that code is running, it re-saves the image everytime, overwriting the old one. Isn't this sort of pointless? Wouldn't it use a lot less resources if I just took away this code now since the image is already created and saved on my forum?

Forgive me but i'm new to this function and just used it for the first time. I'm not quite sure how it's intended to be used.