Could anyone tell me why UIImage.ciimage is null

Question

I found that in IOS UIImage can change to CIImage.and there is a property CIImage in UIImage. and when i use the UIImage,UIImage object is

Answer 1

It is because this UIImage is not in fact a CIImage. In other words, UIImage's CIImage is not nil only if the UIImage is backed by a CIImage already (e.g. because it was generated by imageWithCIImage:). You can't use this to magically turn the UIImage into a CIImage, as you seem to be hoping to do.

The documentation is actually pretty clear on this. Always worth a read.