カメラロールにpngで保存
-(void)savePhotoPng:(UIImage*)orizinalSizeImage{
    NSData *imageData = UIImagePNGRepresentation(orizinalSizeImage);
    UIImage *pngimage = [UIImage imageWithData:imageData];
    UIImageWriteToSavedPhotosAlbum(pngimage, self, @selector(image:didFinishSavingWithError:contextInfo:), nil);
}

Documentsフォルダにファイルとして保存
-(NSString*)getPathByFileName:(NSString*)fileName{
    NSString* path=[NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];
    return [path stringByAppendingPathComponent:fileName];
}
NSString*path=[self getPathByFileName:@"test.png"];
NSData*d=UIImagePNGRepresentation(uiimg);
if ([d writeToFile:path atomically:YES]) {
    NSLog(@"save OK - %@",path);
}else{
    NSLog(@"save NG - %@",path);
}