memory - imageWithCGImage make app crashed -

my project automatic reference counting, when use cgbitmapcontextcreateimage , uiimage's method imagewithcgimage, happened. wrote testing code, when code running, memory increased until app crashed.

the device:

[16g, ipad2, retina]

the code:

(uiimage*) createimagebyimage:(uiimage*)img {     cgsize imgsize = img.size;      imgsize.width *= [uiscreen mainscreen].scale;     imgsize.height *= [uiscreen mainscreen].scale;      cgcolorspaceref space = cgcolorspacecreatedevicergb();     cgcontextref ctx = cgbitmapcontextcreate(nil, imgsize.width, imgsize.height, 8, imgsize.width * (cgcolorspacegetnumberofcomponents(space) + 1), space, kcgimagealphapremultipliedlast);     cgcolorspacerelease(space);      cgrect rect;     rect.origin = cgpointmake(0, 0);     rect.size = imgsize;      // here bypass transformation cgcontext      cgcontextdrawimage(ctx, rect, img.cgimage);      cgimageref cgimage = cgbitmapcontextcreateimage(ctx);     cgcontextrelease(ctx);      uiimage* image = [uiimage imagewithcgimage:cgimage scale:[uiscreen mainscreen].scale orientation:uiimageorientationdown];     cgimagerelease(cgimage);      return image; } 

the caller:

uiimage* baseimg = [uiimage imagenamed:@"corkboard.jpg"]; // big image,e.g. 1024*768 (int = 0; < 100;  i++) {     uiimage* tempimg = [self createimagebyimage:baseimg];     tempimg = nil; } baseimg = nil; 

is there can explain? waiting help!!!

another thing: in code, if replace

[uiimage imagewithcgimage:cgimage ....]; 

with

[uiimage imagewithcgimage:img.cgimage ....]; 

the error disappeared! function changed, not met original demand!