Memory not freed with CIImage

FROM : Stefano Falda
DATE : Wed Jun 11 23:53:19 2008

Hello,
  I've got some code similar to the following, in which I loop in a 
list of image files and  draw their content to another image.

I'm working with X-Code3 under Leopard with Garbage Collection ON, but 
something seems to go wrong, because at the end of all the operations 
the memory is not released (in Activity Monitor there are >400 MB 
still active that disappear if I close my application).

I've tried using NSImage instead of CIImage and everything seems to 
work ok, the memory goes up and then down to where it was before the 
operation, but the process takes 1.5>2 times more than with CIImage.

This is an extract of the code:

for (id loopItem in images) {
           NSString * imageFileName=(NSString*) loopItem;

           destRect=NSMakeRect(currentPos.x, currentPos.y, mosaicSize.width, 
mosaicSize.height);

           CIImage* thisImage2=[CIImage imageWithContentsOfURL:[NSURL 
fileURLWithPath:imageFileName]];
           if (thisImage2!=NULL)
           {
               [thisImage2 drawInRect:destRect fromRect:NSMakeRect(0,0, 
[thisImage2 extent].size.width,[thisImage2 extent].size.height) 
operation:NSCompositeSourceOver                     fraction:1.0];    
           }
       }
       
Maybe I'm missing something very stupid, because I'm new to Objective-
C and Mac Programming.

I thought that, being a newbie, using Garbage Collection I could ease 
my life, but I'm thinking if I need to recode this project with 
standard memory management.

I hope that someone can explain where I'm making something wrong.

Thank you

Stefano