$imgName    =   "codingslover.jpg";
$webPName   =   "codingslover.webp";

Syntax:

 cwebp [quality qualitypercentage] [source image] -o [destination]

exec("cwebp -q 0 ".$imgName." -o ".$webPName." ");

Anthor Method:

exec("convert -colorspace RGB ".$imgName." ".$webPName . " ");