make-image-from-port makes an image out of the specified rectangle of the port's contents. The default is the whole port, but a region can be specified using
x, y, width,
. The default value of
Normally the image is freed automatically, when port is destroyed. However there are circumstances where you need to explicitly free an image, for example when you want it to go away before the port. If the image is not freed, a memory leak occurs.
CAPI User Guide and Reference Manual (Windows version) - 3 Aug 2017