Reference for ultralytics/engine/predictor.py

class BasePredictor:
    """
    BasePredictor.

    A base class for creating predictors.

    Attributes:
        args (SimpleNamespace): Configuration for the predictor.
        save_dir (Path): Directory to save results.
        done_warmup (bool): Whether the predictor has finished setup.
        model (nn.Module): Model used for prediction.
        data (dict): Data configuration.
        device (torch.device): Device used for prediction.
        dataset (Dataset): Dataset used for prediction.
        vid_writer (dict): Dictionary of {save_path: video_writer, ...} writer for saving video output.
    """

    def __init__(self, cfg=DEFAULT_CFG, overrides=None, _callbacks=None):
        """
        Initializes the BasePredictor class.

        Args:
            cfg (str, optional): Path to a configuration file. Defaults to DEFAULT_CFG.
            overrides (dict, optional): Configuration overrides. Defaults to None.
        """
        self.args = get_cfg(cfg, overrides)
        self.save_dir = get_save_dir(self.args)
        if self.args.conf is None:
            self.args.conf = 0.25  # default conf=0.25
        self.done_warmup = False
        if self.args.show:
            self.args.show = check_imshow(warn=True)

        # Usable if setup is done
        self.model = None
        self.data = self.args.data  # data_dict
        self.imgsz = None
        self.device = None
        self.dataset = None
        self.vid_writer = {}  # dict of {save_path: video_writer, ...}
        self.plotted_img = None
        self.source_type = None
        self.seen = 0
        self.windows = []
        self.batch = None
        self.results = None
        self.transforms = None
        self.callbacks = _callbacks or callbacks.get_default_callbacks()
        self.txt_path = None
        self._lock = threading.Lock()  # for automatic thread-safe inference
        callbacks.add_integration_callbacks(self)

    def preprocess(self, im):
        """
        Prepares input image before inference.

        Args:
            im (torch.Tensor | List(np.ndarray)): BCHW for tensor, [(HWC) x B] for list.
        """
        not_tensor = not isinstance(im, torch.Tensor)
        if not_tensor:
            im = np.stack(self.pre_transform(im))
            im = im[..., ::-1].transpose((0, 3, 1, 2))  # BGR to RGB, BHWC to BCHW, (n, 3, h, w)
            im = np.ascontiguousarray(im)  # contiguous
            im = torch.from_numpy(im)

        im = im.to(self.device)
        im = im.half() if self.model.fp16 else im.float()  # uint8 to fp16/32
        if not_tensor:
            im /= 255  # 0 - 255 to 0.0 - 1.0
        return im

    def inference(self, im, *args, **kwargs):
        """Runs inference on a given image using the specified model and arguments."""
        visualize = (
            increment_path(self.save_dir / Path(self.batch[0][0]).stem, mkdir=True)
            if self.args.visualize and (not self.source_type.tensor)
            else False
        )
        return self.model(im, augment=self.args.augment, visualize=visualize, embed=self.args.embed, *args, **kwargs)

    def pre_transform(self, im):
        """
        Pre-transform input image before inference.

        Args:
            im (List(np.ndarray)): (N, 3, h, w) for tensor, [(h, w, 3) x N] for list.

        Returns:
            (list): A list of transformed images.
        """
        same_shapes = len({x.shape for x in im}) == 1
        letterbox = LetterBox(self.imgsz, auto=same_shapes and self.model.pt, stride=self.model.stride)
        return [letterbox(image=x) for x in im]

    def postprocess(self, preds, img, orig_imgs):
        """Post-processes predictions for an image and returns them."""
        return preds

    def __call__(self, source=None, model=None, stream=False, *args, **kwargs):
        """Performs inference on an image or stream."""
        self.stream = stream
        if stream:
            return self.stream_inference(source, model, *args, **kwargs)
        else:
            return list(self.stream_inference(source, model, *args, **kwargs))  # merge list of Result into one

    def predict_cli(self, source=None, model=None):
        """
        Method used for CLI prediction.

        It uses always generator as outputs as not required by CLI mode.
        """
        gen = self.stream_inference(source, model)
        for _ in gen:  # noqa, running CLI inference without accumulating any outputs (do not modify)
            pass

    def setup_source(self, source):
        """Sets up source and inference mode."""
        self.imgsz = check_imgsz(self.args.imgsz, stride=self.model.stride, min_dim=2)  # check image size
        self.transforms = (
            getattr(
                self.model.model,
                "transforms",
                classify_transforms(self.imgsz[0], crop_fraction=self.args.crop_fraction),
            )
            if self.args.task == "classify"
            else None
        )
        self.dataset = load_inference_source(
            source=source,
            batch=self.args.batch,
            vid_stride=self.args.vid_stride,
            buffer=self.args.stream_buffer,
        )
        self.source_type = self.dataset.source_type
        if not getattr(self, "stream", True) and (
            self.source_type.stream
            or self.source_type.screenshot
            or len(self.dataset) > 1000  # many images
            or any(getattr(self.dataset, "video_flag", [False]))
        ):  # videos
            LOGGER.warning(STREAM_WARNING)
        self.vid_writer = {}

    @smart_inference_mode()
    def stream_inference(self, source=None, model=None, *args, **kwargs):
        """Streams real-time inference on camera feed and saves results to file."""
        if self.args.verbose:
            LOGGER.info("")

        # Setup model
        if not self.model:
            self.setup_model(model)

        with self._lock:  # for thread-safe inference
            # Setup source every time predict is called
            self.setup_source(source if source is not None else self.args.source)

            # Check if save_dir/ label file exists
            if self.args.save or self.args.save_txt:
                (self.save_dir / "labels" if self.args.save_txt else self.save_dir).mkdir(parents=True, exist_ok=True)

            # Warmup model
            if not self.done_warmup:
                self.model.warmup(imgsz=(1 if self.model.pt or self.model.triton else self.dataset.bs, 3, *self.imgsz))
                self.done_warmup = True

            self.seen, self.windows, self.batch = 0, [], None
            profilers = (
                ops.Profile(device=self.device),
                ops.Profile(device=self.device),
                ops.Profile(device=self.device),
            )
            self.run_callbacks("on_predict_start")
            for self.batch in self.dataset:
                self.run_callbacks("on_predict_batch_start")
                paths, im0s, s = self.batch

                # Preprocess
                with profilers[0]:
                    im = self.preprocess(im0s)

                # Inference
                with profilers[1]:
                    preds = self.inference(im, *args, **kwargs)
                    if self.args.embed:
                        yield from [preds] if isinstance(preds, torch.Tensor) else preds  # yield embedding tensors
                        continue

                # Postprocess
                with profilers[2]:
                    self.results = self.postprocess(preds, im, im0s)
                self.run_callbacks("on_predict_postprocess_end")

                # Visualize, save, write results
                n = len(im0s)
                for i in range(n):
                    self.seen += 1
                    self.results[i].speed = {
                        "preprocess": profilers[0].dt * 1e3 / n,
                        "inference": profilers[1].dt * 1e3 / n,
                        "postprocess": profilers[2].dt * 1e3 / n,
                    }
                    if self.args.verbose or self.args.save or self.args.save_txt or self.args.show:
                        s[i] += self.write_results(i, Path(paths[i]), im, s)

                # Print batch results
                if self.args.verbose:
                    LOGGER.info("\n".join(s))

                self.run_callbacks("on_predict_batch_end")
                yield from self.results

        # Release assets
        for v in self.vid_writer.values():
            if isinstance(v, cv2.VideoWriter):
                v.release()

        # Print final results
        if self.args.verbose and self.seen:
            t = tuple(x.t / self.seen * 1e3 for x in profilers)  # speeds per image
            LOGGER.info(
                f"Speed: %.1fms preprocess, %.1fms inference, %.1fms postprocess per image at shape "
                f"{(min(self.args.batch, self.seen), 3, *im.shape[2:])}" % t
            )
        if self.args.save or self.args.save_txt or self.args.save_crop:
            nl = len(list(self.save_dir.glob("labels/*.txt")))  # number of labels
            s = f"\n{nl} label{'s' * (nl > 1)} saved to {self.save_dir / 'labels'}" if self.args.save_txt else ""
            LOGGER.info(f"Results saved to {colorstr('bold', self.save_dir)}{s}")
        self.run_callbacks("on_predict_end")

    def setup_model(self, model, verbose=True):
        """Initialize YOLO model with given parameters and set it to evaluation mode."""
        self.model = AutoBackend(
            weights=model or self.args.model,
            device=select_device(self.args.device, verbose=verbose),
            dnn=self.args.dnn,
            data=self.args.data,
            fp16=self.args.half,
            batch=self.args.batch,
            fuse=True,
            verbose=verbose,
        )

        self.device = self.model.device  # update device
        self.args.half = self.model.fp16  # update half
        self.model.eval()

    def write_results(self, i, p, im, s):
        """Write inference results to a file or directory."""
        string = ""  # print string
        if len(im.shape) == 3:
            im = im[None]  # expand for batch dim
        if self.source_type.stream or self.source_type.from_img or self.source_type.tensor:  # batch_size >= 1
            string += f"{i}: "
            frame = self.dataset.count
        else:
            match = re.search(r"frame (\d+)/", s[i])
            frame = int(match.group(1)) if match else None  # 0 if frame undetermined

        self.txt_path = self.save_dir / "labels" / (p.stem + ("" if self.dataset.mode == "image" else f"_{frame}"))
        string += "%gx%g " % im.shape[2:]
        result = self.results[i]
        result.save_dir = self.save_dir.__str__()  # used in other locations
        string += result.verbose() + f"{result.speed['inference']:.1f}ms"

        # Add predictions to image
        if self.args.save or self.args.show:
            self.plotted_img = result.plot(
                line_width=self.args.line_width,
                boxes=self.args.show_boxes,
                conf=self.args.show_conf,
                labels=self.args.show_labels,
                im_gpu=None if self.args.retina_masks else im[i],
            )

        # Save results
        if self.args.save_txt:
            result.save_txt(f"{self.txt_path}.txt", save_conf=self.args.save_conf)
        if self.args.save_crop:
            result.save_crop(save_dir=self.save_dir / "crops", file_name=self.txt_path.stem)
        if self.args.show:
            self.show(str(p))
        if self.args.save:
            self.save_predicted_images(str(self.save_dir / p.name), frame)

        return string

    def save_predicted_images(self, save_path="", frame=0):
        """Save video predictions as mp4 at specified path."""
        im = self.plotted_img

        # Save videos and streams
        if self.dataset.mode in {"stream", "video"}:
            fps = self.dataset.fps if self.dataset.mode == "video" else 30
            frames_path = f'{save_path.split(".", 1)[0]}_frames/'
            if save_path not in self.vid_writer:  # new video
                if self.args.save_frames:
                    Path(frames_path).mkdir(parents=True, exist_ok=True)
                suffix, fourcc = (".mp4", "avc1") if MACOS else (".avi", "WMV2") if WINDOWS else (".avi", "MJPG")
                self.vid_writer[save_path] = cv2.VideoWriter(
                    filename=str(Path(save_path).with_suffix(suffix)),
                    fourcc=cv2.VideoWriter_fourcc(*fourcc),
                    fps=fps,  # integer required, floats produce error in MP4 codec
                    frameSize=(im.shape[1], im.shape[0]),  # (width, height)
                )

            # Save video
            self.vid_writer[save_path].write(im)
            if self.args.save_frames:
                cv2.imwrite(f"{frames_path}{frame}.jpg", im)

        # Save images
        else:
            cv2.imwrite(save_path, im)

    def show(self, p=""):
        """Display an image in a window using OpenCV imshow()."""
        im = self.plotted_img
        if platform.system() == "Linux" and p not in self.windows:
            self.windows.append(p)
            cv2.namedWindow(p, cv2.WINDOW_NORMAL | cv2.WINDOW_KEEPRATIO)  # allow window resize (Linux)
            cv2.resizeWindow(p, im.shape[1], im.shape[0])  # (width, height)
        cv2.imshow(p, im)
        cv2.waitKey(300 if self.dataset.mode == "image" else 1)  # 1 millisecond

    def run_callbacks(self, event: str):
        """Runs all registered callbacks for a specific event."""
        for callback in self.callbacks.get(event, []):
            callback(self)

    def add_callback(self, event: str, func):
        """Add callback."""
        self.callbacks[event].append(func)