Saving and Retrieving Image Makes App Working Slowly - iphone

Question

I save picture from UIImagePicker this way:
Save picture in file and then I save path to the fail in NSUserDefaults and then in another class I retrieve the picture by this saved path.
Code:
-(void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
ideaImage.image = [info objectForKey:#"UIImagePickerControllerOriginalImage"];
[picker dismissModalViewControllerAnimated:YES];
}
-(void)saveIdea_alt
{
[self performSelector: #selector(saveIdea) withObject:nil afterDelay:0.1];
}
-(void)saveIdea
{
UIImage *ideaPhoto = ideaImage.image;
NSData *imageData = UIImagePNGRepresentation(ideaPhoto);
NSString* imageName = #"MyImage.png";
NSArray* paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString* documentsDirectory = [paths objectAtIndex:0];
NSString* fullPathToFile = [documentsDirectory stringByAppendingPathComponent:imageName];
[imageData writeToFile:fullPathToFile atomically:NO];
NSArray *arrayKeys = [[NSArray alloc]initWithObjects:#"ideaName",#"ideaCost",#"ideaNote", #"ideaImage", nil];
NSArray *arrayObjects = [[NSArray alloc]initWithObjects:ideaName.text,ideaCost.text,ideaNote.text,fullPathToFile , nil];
NSDictionary *dictionary = [[NSDictionary alloc]initWithObjects:arrayObjects forKeys:arrayKeys];
NSMutableArray *ideasArray = [[NSMutableArray alloc]initWithArray:[[NSUserDefaults standardUserDefaults]objectForKey:#"ideasArray"]];
[ideasArray addObject:dictionary];
[[NSUserDefaults standardUserDefaults]setObject:ideasArray forKey:#"ideasArray"];
[self dismissModalViewControllerAnimated:YES];
}
However, after that my app becomes slow and it saves and loads images slowly. What I do wrong ?
I don't really want to use Core Data because I already save all others properties of idea in NSUserDefaults (like cost, name, color and etc.)

Answer 1

After setting values in NSUserDefaults,Just write this line :
[[NSUserDefaults standardUserDefaults] synchronize];
Hope this will help.

Answer 2

Have you tried using
[self performSelectorInBackground: #selector(saveIdea) withObject:nil];
instead of
[self performSelector: #selector(saveIdea) withObject:nil afterDelay:0.1];