Get back original size (height, width) from UIImage load with imageWithData

I just cant find useful information from web.

I have an UIImage which loaded from sqlLite with method imageWithData(NSData*), I just find the height and width of the size both be zero. I wanna get back t开发者_Python百科he original height and width of the image, is it possible? or I do need to store these information separately in sqllite?

Size property of UIImage will work fine.

UIImage *image=[UIImage imageWithData:@"slide"];

NSLog(@"WIDTH = %f and HEIGHT = %f\n",image.size.width,image.size.height);

What's wrong with using the UIImage property size?