This function seems to do the same thing as photoshop feture convas size, you set size of convas and position of your image's top left corner (x,y) inside that convas.
(No version information available, might only be in Git)
Imagick::resetImagePage — Reset image page
The page definition as a string. The string is in format WxH+x+y. This method is available if Imagick has been compiled against ImageMagick version 6.3.6 or newer.
The page definition. For example 7168x5147+0+0
TRUE on success.