I have an image like:

When I load the image to uiimageview and then adding as a subvie
Probably you are looking for this,
UIImageView *tempImageView = [[[UIImageView alloc] initWithImage:[UIImage imageNamed:@"Watson.jpg"]] autorelease];
tempImageView.frame = scrollView.bounds;
self.imageView = tempImageView;
scrollView.backgroundColor = [UIColor blackColor];
scrollView.minimumZoomScale = 1.0 ;
scrollView.maximumZoomScale = imageView.image.size.width / scrollView.frame.size.width;
scrollView.zoomScale = 1.0;
scrollView.delegate = self;
[scrollView addSubview:imageView];