Overview
A UIImage object is a high-level way to display image data. You can create images from files, from Quartz image objects, or from raw image data you receive. The UIImage class also offers several options for drawing images to the current graphics context using different blend modes and opacity values.
Image objects are immutable, so you cannot change their properties after creation. This means that you generally specify an image’s properties at initialization time or rely on the image’s metadata to provide the property value. In some cases, however, the UIImage class provides convenience methods for obtaining a copy of the image that uses custom values for a property.
Because image objects are immutable, they also do not provide direct access to their underlying image data. However, you can get an NSData object containing either a PNG or JPEG representation of the image data using the UIImagePNGRepresentation and UIImageJPEGRepresentation functions.
Images and Memory Management
In low-memory situations, image data may be purged from a UIImage object to free up memory on the system. This purging behavior affects only the image data stored internally by the UIImage object and not the object itself. When you attempt to draw an image whose data has been purged, the image object automatically reloads the data from its original file. This extra load step, however, may incur a small performance penalty.
It is a programmer error to create a UIImage object with an image that is greater than 1024 x 1024 pixels in size. Besides the practical considerations of such an image consuming a large amount of memory, the graphics hardware does not support images greater than that size.
Click the link to find out the Tutorials Download from Apple.com
https://developer.apple.com/iphone/library/documentation/UIKit/Reference/UIImage_Class/Reference/Reference.html#//apple_ref/occ/instm/UIImage/drawAtPoint:
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