Using iOS CIDetector face detection to trigger function

Question

I am trying to make a Face detector using CIDetector that enables a button as long as the face is detected. The part that I search for and I couldn't find is how to make the code trigger a function when it detects a face. And disable it when the face leaves camera frame.

Here is the code that I have until now:

.h file:

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController

@property (weak, nonatomic) IBOutlet UIButton *actionButton;
//Update 2:
@property (weak, nonatomic) IBOutlet UIView *containerView;

- (IBAction)actionButton:(id)sender;

@end

.m file:

#import "ViewController.h"
@import AVFoundation;

@interface ViewController () <AVCaptureMetadataOutputObjectsDelegate> {
    AVCaptureVideoPreviewLayer *_previewLayer;
    AVCaptureSession *_session;
    CIDetector *_faceDetector;
    CIContext *_ciContext;
}

@end

@implementation SCViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.


    // Create a new AVCaptureSession
    _session = [[AVCaptureSession alloc] init];
    [_session setSessionPreset:AVCaptureSessionPreset640x480];
    AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    NSError *error = nil;


    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error];

    if(input) {
        // Add the input to the session
        [_session addInput:input];
    } else {
        NSLog(@"error: %@", error);
        return;
    }

    AVCaptureMetadataOutput *output = [[AVCaptureMetadataOutput alloc] init];
    // Have to add the output before setting metadata types
    [_session addOutput:output];

    // Restrict the output metadata to faces
    [output setMetadataObjectTypes:@[AVMetadataObjectTypeFace]];
    // This VC is the delegate. Please call us on the main queue
    [output setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];


    // Display on screen
    _previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:_session];
    _previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
    _previewLayer.bounds = self.view.bounds;
    _previewLayer.position = CGPointMake(CGRectGetMidX(self.view.bounds), CGRectGetMidY(self.view.bounds));
    // Update 2 change 
    [self.containerView.layer addSublayer:_previewLayer];
    // Hide the button
     self.actionButton.hidden = YES;
    // Start the AVSession running
    [_session startRunning];
}



// Update 1:

- (void)captureOutput:(AVCaptureOutput *)captureOutput
didOutputMetadataObjects:(NSArray *)metadataObjects
       fromConnection:(AVCaptureConnection *)connection
{
    for(AVMetadataObject *metadataObject in metadataObjects) {
        if([metadataObject.type isEqualToString:AVMetadataObjectTypeFace]) {

            self.retakeButton.hidden = NO;
        }
    }
}

- (IBAction)actionButton:(id)sender {

}    
@end

Have You checked AVCaptureMetadataOutput delegate methods? `- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection` this sohuld be called after face is detected. Here's more info: http://stackoverflow.com/questions/18995236/ios-7-avcapturemetadataoutput-delegate-qrcode-scanner — Mateusz Szlosek, Jan 15 '15 at 15:25
I Have added the suggested function but it seems to do nothing.. — Bianca Ioana, Jan 15 '15 at 15:40
@BiancaIoana you might have to do `self.retakeButton.hidden = NO;` on a UI thread. — kiranpradeep, Jan 15 '15 at 15:43
@MateuszSzlosek It enters the function but the self.retakeButton.hidden = NO; is not called — Bianca Ioana, Jan 15 '15 at 16:32
Please add `NSLog(@"%@",metadataObjects);` inside the delegate method and paste the output. — Mateusz Szlosek, Jan 15 '15 at 16:46

Laur Stefan · Accepted Answer · 2015-01-16T09:16:49.583

In your storyboard you should add a new view to the main view and create the outlet:

@property (weak, nonatomic) IBOutlet UIView *containerView;

And the button that you add should be on the same hierarchical as the newly created subview. Also the button should be in front of the newly created subview.

And in your code change:

[self.view.layer addSublayer:_previewLayer];

to:

[self.containerView.layer addSublayer:_previewLayer];

Hope these help

Update:

If you had gesture recognizer and no UI for it than you could have used this quick and easy fix:

 NSTimer *timer = [NSTimer timerWithTimeInterval:0.2f target:self selector:@selector(hideButton) userInfo:nil repeats:YES];
    [[NSRunLoop mainRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];

Where:

-(void)hideButton{

    if(counterSeconds==2){
        if (counterCaptureOutput==0) {
            NSLog(@"hide button");
             [self.retakeButton setHidden:YES];
        }
        counterCaptureOutput=0;
        counterSeconds=0;
    }
    counterSeconds++;
}

and:

- (void)captureOutput:(AVCaptureOutput *)captureOutput
didOutputMetadataObjects:(NSArray *)metadataObjects
       fromConnection:(AVCaptureConnection *)connection
{
    for(AVMetadataObject *metadataObject in metadataObjects) {
        if([metadataObject.type isEqualToString:AVMetadataObjectTypeFace]) {
            self.retakeButton.hidden = NO;
            counterCaptureOutput++;
            NSLog(@"ENTER FUNCTION");
        }
    }
}

Also include in .m:

int counterCaptureOutput;
int counterSeconds;

It seams to do the, trick the button is displayed on screen when it detects a face. But, it doesn't get hidden when the face disappears from the frame of the camera. How can I fix it? — Bianca Ioana, Jan 15 '15 at 17:25
Should I use a completion handler to set the button to hidden=no when it finishes running captureOutput? And if so, how would I do that? — Bianca Ioana, Jan 15 '15 at 17:32

Using iOS CIDetector face detection to trigger function

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