Image processing by linking java and matlab

I am working on high resolution images like 2592x3872. But when i load these images in matlab using java classes it shows the error "java.lang.OutOfMemoryError: Java heap space". Now i have tried increasing the JVM space by creating java.opts file in the startup but it is not proving of any help. Can someone tell me how can i unallocate the space because the below mentioned link clearly says that "CLEAR, PACK, QUIT commands do not affect the Java class objects created by the Java Virtual Machine (JVM)"... http://www.mathworks.com/support/tech-notes/1100/1106.html

and how much space do i need to allocate for these sized images in case i make a java.opts file.???