画像のメモリ削減管理

viewImage.image = nil;//既に画像の読み込まれたUIImageView
NSString *imageName = [NSString stringWithFormat: @"img2"];//新しくのせかえるUIImage
NSString *imagePath = [[NSBundle mainBundle] pathForResource:imageName ofType:@"png"];
img = [[UIImage alloc] initWithContentsOfFile:imagePath];
viewImage.image = img;
viewImage.contentMode = UIViewContentModeScaleAspectFill;
[img release];