CIDetector Edge identification

CIDetector. H comes with four recognition functions under CoreImage

/ * Face recognition */CORE_IMAGE_EXPORT NSString* const CIDetectorTypeFace NS_AVAILABLE(10 _7.5 _0); / * Rectangle edge recognition */CORE_IMAGE_EXPORT NSString* const CIDetectorTypeRectangle NS_AVAILABLE(10 _10.8 _0);

/* Qr code recognition */
CORE_IMAGE_EXPORT NSString* const CIDetectorTypeQRCode NS_AVAILABLE(10 _10.8 _0);

/* Text recognition */
#if __OBJC2__
CORE_IMAGE_EXPORT NSString* const CIDetectorTypeText NS_AVAILABLE(10 _11.9 _0);
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Then, CIDetectorTypeRectangle was used to identify the rectangular edge of the image. The effect picture is as follows (shown at the bottom of the Demo link)

Part code:

• Initialize a high-precision recognizer

// High precision edge recognizer
- (CIDetector *)highAccuracyRectangleDetector
{
    static CIDetector *detector = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^
                  {
                      detector = [CIDetector detectorOfType:CIDetectorTypeRectangle context:nil options:@{CIDetectorAccuracy : CIDetectorAccuracyHigh}];
                  });
    return detector;
}
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• Call the camera to capture the camera image

NSArray *possibleDevices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
    AVCaptureDevice *device = [possibleDevices firstObject];
    if(! device)return;
    
    _imageDedectionConfidence = 0.0;
    
    AVCaptureSession *session = [[AVCaptureSession alloc] init];
    self.captureSession = session;
    [session beginConfiguration];
    self.captureDevice = device;
    
    NSError *error = nil;
    AVCaptureDeviceInput* input = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error];
    session.sessionPreset = AVCaptureSessionPresetPhoto;
    [session addInput:input];
    
    AVCaptureVideoDataOutput *dataOutput = [[AVCaptureVideoDataOutput alloc] init];
    [dataOutput setAlwaysDiscardsLateVideoFrames:YES];
    [dataOutput setVideoSettings:@{(id)kCVPixelBufferPixelFormatTypeKey:@(kCVPixelFormatType_32BGRA)}];
    [dataOutput setSampleBufferDelegate:self queue:dispatch_get_main_queue()];
    [session addOutput:dataOutput];
    
    self.stillImageOutput = [[AVCaptureStillImageOutput alloc] init];
    [session addOutput:self.stillImageOutput];
    
    AVCaptureConnection *connection = [dataOutput.connections firstObject];
    [connection setVideoOrientation:AVCaptureVideoOrientationPortrait];
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• You also need a container that displays captured images

 self.context = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
    GLKView *view = [[GLKView alloc] initWithFrame:self.bounds];
    view.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
    view.translatesAutoresizingMaskIntoConstraints = YES;
    view.context = self.context;
    view.contentScaleFactor = 1.0f;
    view.drawableDepthFormat = GLKViewDrawableDepthFormat24;
    [self insertSubview:view atIndex:0];
    _glkView = view;
    glGenRenderbuffers(1, &_renderBuffer);
    glBindRenderbuffer(GL_RENDERBUFFER, _renderBuffer);
    
    // The image will be drawn into _coreImageContext
    _coreImageContext = [CIContext contextWithEAGLContext:self.context];
    [EAGLContext setCurrentContext:self.context];
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• followAVCaptureVideoDataOutputSampleBufferDelegateThe agent, after capturing the image, calls the following methods

-(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
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Call CIDetector for identification and obtain the maximum quadrilateral irregularity

// Get the CIImage from the buffer
CVPixelBufferRef pixelBuffer = (CVPixelBufferRef)CMSampleBufferGetImageBuffer(sampleBuffer);
CIImage *image = [CIImage imageWithCVPixelBuffer:pixelBuffer];
 // Use high precision edge recognizer to identify features
NSArray <CIFeature *>*features = [[self highAccuracyRectangleDetector] featuresInImage:image];
// Select the largest quadrilateral in the feature list
 _borderDetectLastRectangleFeature = [self biggestRectangleInRectangles:features];
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• Use after identifying edgesCAShapeLayerDraws and displays the edges

// Draw the edge detection layer
- (void)drawBorderDetectRectWithImageRect:(CGRect)imageRect topLeft:(CGPoint)topLeft topRight:(CGPoint)topRight bottomLeft:(CGPoint)bottomLeft bottomRight:(CGPoint)bottomRight
{
    
    if(! _rectOverlay) { _rectOverlay = [CAShapeLayer layer];
        _rectOverlay.fillRule = kCAFillRuleEvenOdd;
        _rectOverlay.fillColor = [UIColor colorWithRed:73/255.0 green:130/255.0 blue:180/255.0 alpha:0.4].CGColor;
        _rectOverlay.strokeColor = [UIColor whiteColor].CGColor;
        _rectOverlay.lineWidth = 5.0f;
    }
    if(! _rectOverlay.superlayer) {self.layer.masksToBounds = YES;
        [self.layer addSublayer:_rectOverlay];
    }

    // Convert the image space coordinate system to UIKit coordinate system
    TransformCIFeatureRect featureRect = [self transfromRealRectWithImageRect:imageRect topLeft:topLeft topRight:topRight bottomLeft:bottomLeft bottomRight:bottomRight];
    
    // Edge recognition path
    UIBezierPath *path = [UIBezierPath new];
    [path moveToPoint:featureRect.topLeft];
    [path addLineToPoint:featureRect.topRight];
    [path addLineToPoint:featureRect.bottomRight];
    [path addLineToPoint:featureRect.bottomLeft];
    [path closePath];
    // Background mask path
    UIBezierPath *rectPath  = [UIBezierPath bezierPathWithRect:CGRectMake(-5,
                                                                          -5.self.frame.size.width + 10.self.frame.size.height + 10)];
    [rectPath setUsesEvenOddFillRule:YES];
    [rectPath appendPath:path];
    _rectOverlay.path = rectPath.CGPath;
}
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Now you can see the effect of real-time identification

• Finally, after taking photos, the filter will be used to convert the irregular quadrilateral identified into a rectangle, which can be converted into a square rectangle

/// Convert any quadrilateral into a square
- (CIImage *)correctPerspectiveForImage:(CIImage *)image withFeatures:(CIRectangleFeature *)rectangleFeature
{
    NSMutableDictionary *rectangleCoordinates = [NSMutableDictionary new];
    rectangleCoordinates[@"inputTopLeft"] = [CIVector vectorWithCGPoint:rectangleFeature.topLeft];
    rectangleCoordinates[@"inputTopRight"] = [CIVector vectorWithCGPoint:rectangleFeature.topRight];
    rectangleCoordinates[@"inputBottomLeft"] = [CIVector vectorWithCGPoint:rectangleFeature.bottomLeft];
    rectangleCoordinates[@"inputBottomRight"] = [CIVector vectorWithCGPoint:rectangleFeature.bottomRight];
    return [image imageByApplyingFilter:@"CIPerspectiveCorrection" withInputParameters:rectangleCoordinates];
}
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// TODO: After an edge is identified, you can manually set the edge range

Demo address: making portal: https://github.com/madaoCN/MADRectDetect man points under the Star