how to convert uiimage to string and string to data in ios?

how to convert uiimage to string and string to data in ios?

• first convert your image image into image data

NSData *imageData = UIImagePNGRepresentation(imgw_ProfPic.image);

• nsdata to nsstring

NSString *imageStr = [GTMBase64 stringByEncodingData:imageData];

• nsstring to nsdata 

NSData *imageData = [GTMBase64 decodeString:imageStr];