如何通过AVCaptureMetadataOutput或Vision检测条形码水平翻转？

我有两个条形码，内容都是数字01069327，唯一区别是第二个条形码被水平翻转。出于业务需求，我需要识别出这种翻转状态。尝试用AVFoundation和Vision框架实现，但两种方案始终返回相同的状态值1，无法区分翻转状态。但在线条码识别工具能正确检测旋转状态，请问有没有方法获取翻转信息？也可以使用免费第三方库。

使用AVFoundation的尝试代码 #

func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {

    if let metadataObject = metadataObjects.first {
        guard let readableObject = metadataObject as? AVMetadataMachineReadableCodeObject else { return }
        guard let stringValue = readableObject.stringValue else { return }
        
        let topLeft = readableObject.corners[0]
        let topRight = readableObject.corners[1]
        let bottomRight = readableObject.corners[2]
        let bottomLeft = readableObject.corners[3]

        let diffXRight = topRight.x - bottomRight.x
        let diffXLeft = topLeft.x - bottomLeft.x
        let flipThresholdX: CGFloat = 0.01
        let isFlippedHorizontally = abs(diffXRight) > flipThresholdX || abs(diffXLeft) > flipThresholdX

        print("BARCODE: \(stringValue), flipped: \(isFlippedHorizontally ? 0 : 1)\n\n")
        self.parent.didFindCode(stringValue, isFlippedHorizontally ? 0 : 1)
    }

}

使用Vision的尝试代码 #

private func createRequest() -> VNDetectBarcodesRequest {
    let request = VNDetectBarcodesRequest { request, error in
        [...]
        if let stringValue = observation.payloadStringValue {
            let topLeft = observation.topLeft
            let topRight = observation.topRight
            let bottomLeft = observation.bottomLeft
            
            let angle = atan2(topRight.y - topLeft.y, topRight.x - topLeft.x) * 180.0 / .pi
            let rotationThreshold: Float = 180.0
            let isFlippedHorizontally = angle > rotationThreshold || angle < -rotationThreshold
            
            print("BARCODE: \(stringValue), flipped: \(isFlippedHorizontally ? 0 : 1)")
            self.parent.didFindCode(stringValue, isFlippedHorizontally ? 0 : 1)
        }
    }
    return request
}

原代码问题分析 #

• AVFoundation方案：框架会自动规整条码的角点顺序，无论条码是否翻转，corners数组的顺序都保持一致，通过左右边X差值无法判断真实翻转状态。
• Vision方案：计算的顶部边角度逻辑错误，水平翻转后该角度仍在±0°左右，不会触发±180°的阈值判断。

可行解决方案 #

方案1：修正Vision框架的判断逻辑 #

Vision返回的条码顶点坐标是归一化的图像坐标（原点在左上角，X向右递增），水平翻转的条码会出现topLeft.x > topRight.x的特征，直接对比即可：

private func createRequest() -> VNDetectBarcodesRequest {
    let request = VNDetectBarcodesRequest { request, error in
        guard let observations = request.results as? [VNBarcodeObservation],
              let observation = observations.first,
              let stringValue = observation.payloadStringValue else { return }
        
        // 水平翻转时，左上角X坐标大于右上角X坐标
        let isFlippedHorizontally = observation.topLeft.x > observation.topRight.x
        
        print("BARCODE: \(stringValue), flipped: \(isFlippedHorizontally ? 0 : 1)")
        self.parent.didFindCode(stringValue, isFlippedHorizontally ? 0 : 1)
    }
    return request
}

方案2：使用免费第三方库ZBarSDK #

ZBar会返回条码的方向信息，可直接区分水平翻转状态：

1. 集成ZBarSDK到项目中
2. 通过ZBarSymbol的orientation属性判断状态，ZBarOrientationLeft或ZBarOrientationRight对应水平翻转

示例代码片段：

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {
    UIImage *image = info[UIImagePickerControllerOriginalImage];
    ZBarImage *zbarImage = [ZBarImage imageWithUIImage:image];
    ZBarScanner *scanner = [ZBarScanner new];
    ZBarSymbolSet *symbols = [scanner scanImage:zbarImage];
    
    for (ZBarSymbol *symbol in symbols) {
        NSString *code = symbol.data;
        BOOL isFlipped = (symbol.orientation == ZBarOrientationLeft || symbol.orientation == ZBarOrientationRight);
        NSLog(@"BARCODE: %@, flipped: %d", code, isFlipped ? 0 : 1);
    }
    [picker dismissViewControllerAnimated:YES completion:nil];
}

方案3：基于条码编码规则判断（特定场景） #

如果是固定类型的条码（如EAN-13），可通过分析起始符/终止符的位置判断：

• EAN-13的起始符为101，终止符也为101，但左右数据符编码规则不同
• 水平翻转后，起始符会出现在条码右侧，可通过图像中黑白条的分布特征识别位置差异

此方法需深入了解条码编码规则，适合特定业务场景。

内容的提问来源于stack exchange，提问作者elp