Android OpenCV实现对小票的截取

目录

效果展示

实现流程

关键代码

关键代码比较简单，这里我是使用官方提供的Java API实现的代码如下

//导入源图像
                    val bitmap: Bitmap = BitmapFactory.decodeResource(resources, R.drawable.img)
                    val src = Mat()
                    Utils.bitmapToMat(bitmap, src) //将bitmap转换为Mat


                    val thresholdImage = Mat(src.size(),src.type())
                    val cannyImage = Mat(src.size(),src.type())

                    //将图像转换为灰度图像
                    Imgproc.cvtColor(src, thresholdImage, Imgproc.COLOR_RGBA2GRAY)
                    //将图像转换为边缘二值图像
                    Imgproc.threshold(thresholdImage,thresholdImage,150.0,255.0,Imgproc.THRESH_BINARY)

                    //查找边缘
                    Imgproc.Canny(thresholdImage, cannyImage, 100.0, 200.0,3)
                    val kernel = Imgproc.getStructuringElement(Imgproc.MORPH_RECT, Size(3.0, 3.0)) //获取结构元素
                    //膨胀操作
                    Imgproc.dilate(cannyImage, cannyImage, kernel)
                    val hierarchy = Mat()
                    val contours: ArrayList = ArrayList()
                    //轮廓发现
                    Imgproc.findContours(
                        cannyImage,
                        contours,
                        hierarchy,
                        Imgproc.RETR_EXTERNAL,
                        Imgproc.CHAIN_APPROX_NONE
                    )

                    //找出最大轮廓
                    var rectMax = Rect()
                    var maxIndex = 0
                    for (i in 0 until contours.size) {
                        val rect = Imgproc.boundingRect(contours[i])
                        if(rect.width * rect.height > rectMax.width * rectMax.height){
                            rectMax = rect
                            maxIndex = i
                        }
                    }

                    //画出小票轮廓
                    val showContoursImg = Mat()
                    src.copyTo(showContoursImg)
                    Imgproc.drawContours(showContoursImg,contours,maxIndex,Scalar(255.0, 0.0, 0.0, 255.0),10, 8)
                    val contoursBitmap = Bitmap.createBitmap(bitmap.width,bitmap.height,bitmap.config)
                    Utils.matToBitmap(showContoursImg,contoursBitmap)
                    activityMainBinding.imgContours.setImageBitmap(contoursBitmap)

                    //找出最大轮廓的四个顶点
                    val points = contours[maxIndex]
                    //左上角顶点
                    var topLeftPoint:Point? = null
                    //右下角顶点
                    var bottomRightPoint:Point? = null
                    //右上角顶点
                    var topRightPoint:Point? = null
                    //左下角顶点
                    var bottomLeftPoint:Point? = null
                    points.toList().forEach {
                        //寻找右上角顶点
                        if(topRightPoint == null){
                            topRightPoint = it
                        }else{
                            if(topRightPoint!!.x / topRightPoint!!.y < it.x / it.y){
                                topRightPoint = it
                            }
                        }
                        //寻找右下角顶点
                        if(bottomRightPoint == null){
                            bottomRightPoint = it
                        }else{
                            if(bottomRightPoint!!.x + bottomRightPoint!!.y < it.x + it.y){
                                bottomRightPoint = it
                            }
                        }
                        //寻找左上角顶点
                        if(topLeftPoint == null){
                            topLeftPoint = it
                        }else{
                            if(topLeftPoint!!.x + topLeftPoint!!.y > it.x + it.y){
                                topLeftPoint = it
                            }
                        }
                        //寻找左下角顶点
                        if(bottomLeftPoint == null){
                            bottomLeftPoint = it
                        }else{
                            if(bottomLeftPoint!!.x / bottomLeftPoint!!.y > it.x / it.y){
                                bottomLeftPoint = it
                            }
                        }
                    }


                    //画出轮廓顶点
                    val showVerticesImg = Mat()
                    src.copyTo(showVerticesImg)
                    Imgproc.circle(showVerticesImg,topLeftPoint,10,Scalar(0.0, 255.0, 0.0, 255.0),50, 8)
                    Imgproc.circle(showVerticesImg,bottomRightPoint,10,Scalar(0.0, 255.0, 0.0, 255.0),50, 8)
                    Imgproc.circle(showVerticesImg,topRightPoint,10,Scalar(0.0, 255.0, 0.0, 255.0),50, 8)
                    Imgproc.circle(showVerticesImg,bottomLeftPoint,10,Scalar(0.0, 255.0, 0.0, 255.0),50, 8)
                    val verticesBitmap = Bitmap.createBitmap(bitmap.width,bitmap.height,bitmap.config)
                    Utils.matToBitmap(showVerticesImg,verticesBitmap)
                    activityMainBinding.imgVertices.setImageBitmap(verticesBitmap)


                    //进行透视变换
                    val fromPoints = MatOfPoint2f(topLeftPoint,topRightPoint,bottomLeftPoint,bottomRightPoint)
                    val toPoints = MatOfPoint2f(
                        Point(0.0,0.0),
                        Point(rectMax.width.toDouble(),0.0),
                        Point(0.0, rectMax.height.toDouble()),
                        Point(rectMax.width.toDouble(), rectMax.height.toDouble())
                    )
                    val transform = Imgproc.getPerspectiveTransform(fromPoints,toPoints)
                    //创建一个与小票一样比例的Bitmap用来存放最终效果图
                    val dstBitmap = Bitmap.createBitmap(rectMax.width,rectMax.height,bitmap.config)
                    //对二值化的图像进行变换（因为这样出来的图文字比较清晰）
                    Imgproc.warpPerspective(thresholdImage,thresholdImage,transform, Size(rectMax.width.toDouble(), rectMax.height.toDouble()))
                    Utils.matToBitmap(thresholdImage, dstBitmap) //将Mat转为Bitmap
                    activityMainBinding.imgDst.setImageBitmap(dstBitmap)


                    //释放资源
                    thresholdImage.release()
                    cannyImage.release()
                    src.release()
                    showContoursImg.release()
                    showVerticesImg.release()

案例源码

完整的代码如下：
https://gitee.com/itfitness/opencv-cutreceipts