使用CIFilter后传递UIImage的问题

Question

I have a problem that I can't seem to solve or find any SO related posts. I have an image I'm trying to pass into a function, edit with CIFilter and pass back the result for display. However, when the image is passed back it seems to have been released and I have no idea why. Here's the code:

 - (void)viewDidLoad {
    [super viewDidLoad];
    myImageView = [[UIImageView alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    UIImage *image =  [UIImage imageNamed:@"testim.png"];

    UIImage *imout;
    [self editimage: image fpin:imout];
    myImageView.image = imout;
    [self.view addSubview:myImageView];

}


-(void) editimage:(UIImage *) image fpin:(UIImage *) img_new{
        CIImage *ciImage = [CIImage imageWithCGImage:[image CGImage]];

        CIFilter *filter = [CIFilter filterWithName:@"CISepiaTone"
                                      keysAndValues: kCIInputImageKey, ciImage,
                            @"inputIntensity", @0.8, nil];
        CIImage *outputImage = [filter outputImage];

        CIContext *context = [CIContext contextWithOptions:nil];
        CGImageRef cgimage = [context createCGImage:outputImage fromRect:[outputImage extent]];
        img_new = [UIImage imageWithCGImage:cgimage];
        CGImageRelease(cgimage);
    }

Can anyone shed some light on this?

Answer 1

The problem with your code is that in fact it does not change your output image at all. Your editimage method assigns an image to local copy of imout .

You have two options:

Option 1

Return the modified image:

-(UIImage*) editimage:(UIImage *) image {
    ...

    UIImage *newImage = [UIImage imageWithCGImage:cgimage];
    CGImageRelease(cgimage);
    return newImage
}

And in your viewDidLoad:

UIImage *imout = [self editimage:image];

Option 2

If you really want to stick with your original pattern, you can pass the reference to your image:

-(void) editimage:(UIImage *) image fpin:(UIImage **) img_new {
    ...
    *img_new = [UIImage imageWithCGImage:cgimage];
    CGImageRelease(cgimage);
}

And in your viewDidLoad:

[self editimage: image fpin:&imout];