从文本检测中获取最大行的图像

Question

如何快速从文本检测中获取最大线条的图像？ 我在我的项目中使用Vision框架使用textdetection。但我被困在textdetetcion的图像裁剪中。我的代码就像，

// MARK: - Draw
    func drawRegionBox(box: VNTextObservation) {
        guard let boxes = box.characterBoxes else {return}
        //print(boxes.count)
        var xMin: CGFloat = 9999.0
        var xMax: CGFloat = 0.0
        var yMin: CGFloat = 9999.0
        var yMax: CGFloat = 0.0

        for char in boxes {

            if char.bottomLeft.x < xMin {xMin = char.bottomLeft.x}
            if char.bottomRight.x > xMax {xMax = char.bottomRight.x}
            if char.bottomRight.y < yMin {yMin = char.bottomRight.y}
            if char.topRight.y > yMax {yMax = char.topRight.y}
        }

        let xCoord = xMin * previewView.frame.size.width
        let yCoord = (1 - yMax) * previewView.frame.size.height
        let width = (xMax - xMin) * previewView.frame.size.width
        let height = (yMax - yMin) * previewView.frame.size.height

        let layer = CALayer()
        layer.frame = CGRect(x: xCoord, y: yCoord, width: width, height: height)
        layer.borderWidth = 2.0
        layer.borderColor = UIColor.green.cgColor
        }