Returns an NSBitmapImageRep object created from a Core Graphics image object.
A Core Graphics image object (an opaque type) from which to create the receiver. This opaque type is retained.
An NSBitmapImageRep object initialized from the contents of the Core Graphics image.
If you use this method, you should treat the resulting bitmap NSBitmapImageRep object as read only. Because it only retains the value in the cgImage parameter, rather than unpacking the data, accessing the pixel data requires the creation of a copy of that data in memory. Changes to that data are not saved back to the Core Graphics image.