1.处理为灰度
2.确定一下圆的大小
3.找出黑色点,然后根据半径计算点,统计次半径下,点数之和.
4.最大的点就是圆心所在
5.画出找出的圆

    public void run(){
        Pixmap pixmap = new Pixmap(Gdx.files.internal("screenshot.png"));
        Image im = new Image(new Texture(pixmap));
        addActor(im);
        im.addAction(Actions.forever(
                Actions.sequence(
                Actions.fadeOut(6),
                Actions.fadeIn(6)
                )));
        int width = pixmap.getWidth();
        int height = pixmap.getHeight();
        int MIN_RADIUS = 20;
        int MAX_RADIUS = 21;
        int[][][] accumulator = new int[width][height][MAX_RADIUS - MIN_RADIUS + 1];
        ByteBuffer pixels = pixmap.getPixels();

//        for (int i = 0; i < 360; i++) {
//            Image image = new Image(Asset.getAsset().getTexture("white_bg.png"));
//            addActor(image);
//            image.setSize(1,1);
//            image.setColor(Color.RED);
//            image.setPosition((float) (180+MAX_RADIUS*Math.cos(i)), (float) (380+MAX_RADIUS*Math.sin(i)),Align.center);
//        }


//        for (int i = 0; i < height; i++) {
//            for (int i1 = 0; i1 < width; i1++) {
//                int pixel = pixmap.getPixel(i, i1);
//                float r = (pixel >> 24 & 0xFF) / 255f;
//                float g = (pixel >> 16 & 0xFF) / 255f;
//                float b = (pixel >> 8 & 0xFF) / 255f;
//
//
//                if (r==0&&g==0&&b==0) {
//                    Image image = new Image(Asset.getAsset().getTexture("white_bg.png"));
//                    addActor(image);
//                    image.setColor(Color.BLACK);
//                    image.setPosition(i,i1);
//                }
//
//            }
//        }
        for (int y = 0; y <height; y++) {
            for (int x = 0; x < width; x++) {
                int pixel = pixmap.getPixel(x, height-y-1);
                float r = (pixel >> 24 & 0xFF) / 255f;
                float g = (pixel >> 16 & 0xFF) / 255f;
                float b = (pixel >> 8 & 0xFF) / 255f;


                if (r==0&&g==0&&b==0) {
                    // Edge pixel
                    for (int rad = MIN_RADIUS; rad <= MAX_RADIUS; rad++) {
                        for (int theta = 0; theta < 360; theta+=1) {
                            int a = (int)(x - rad * Math.cos(Math.toRadians(theta)));
                            int b1 = (int)(y - rad * Math.sin(Math.toRadians(theta)));
                            if (a >= 0 && a < width-2 && b1 >= 0 && b1 < height-2) {
                                accumulator[a][b1][rad - MIN_RADIUS]++;
//                                if (accumulator[a][b1][rad - MIN_RADIUS]==1) {
//                                    Image image = new Image(Asset.getAsset().getTexture("white_bg.png"));
//                                    addActor(image);
//                                    image.setSize(1, 1);
//                                    image.setPosition(x, y, Align.center);
//                                    image.setColor(Color.BLACK);
//                                    image.getColor().a = 0.2f;
//                                }
                            }
                        }
                    }
                    // Edge pixel
//                                    Image image = new Image(Asset.getAsset().getTexture("white_bg.png"));
//                                    addActor(image);
//                                    image.setPosition(y, x, Align.center);
//                                    image.setColor(Color.BLACK);
//                                    image.setSize(1, 1);
//                                    image.getColor().a = 0.2f;
                }else {

//                    System.out.println("------out-------");
                }
            }
        }



//
        for (int y = 0; y < height-4; y++) {
            for (int x = 0; x < width-4; x++) {
                for (int r = MIN_RADIUS; r <= MAX_RADIUS; r++) {
                    if (accumulator[x][y][r - MIN_RADIUS] >= 360) {
//                        System.out.println(accumulator[x][y][r - MIN_RADIUS]);
//                        System.out.println("---------------");
                        Image image = new Image(Asset.getAsset().getTexture("white_bg.png"));
                        addActor(image);
                        image.setSize(1,1);
                        image.setPosition(x,y,Align.center);
                        image.setColor(Color.BLACK);
                        Bean bean = new Bean();
                        bean.x = x;
                        bean.y = y;
                        bean.radius = MAX_RADIUS;
                        array.add(bean);

//                        image.setDebug(true);
//                        System.out.println(accumulator[x][y][r - MIN_RADIUS]);
                    }
                    }
//              }
            }
        }

//        Pixmap pixmap1 = new Pixmap(Gdx.files.internal("cirtest2.png"));
//        Image image = new Image(new Texture(pixmap1));
//        addActor(image);
    }

    private Array<Bean> array = new Array<>();
    @Override
    public void render(float delta) {
        super.render(delta);

        renderer.begin(ShapeRenderer.ShapeType.Line);
        renderer.setColor(Color.RED);

        for (Bean bean : array) {
            renderer.circle(bean.x,bean.y,bean.radius);
        }

        renderer.end();
    }

    class Bean{
        private float x;
        private float y;
        private float radius;
    }
}

image.png