【亲测】解决使用super_gradients库预测图片无法获取预测结果图片

问题

在使用super_gradients库中的Yolo-nas预测图片时，想要获取预测好的图片，但执行out = model.predict(“camera01.png”, conf=0.6, batch_size=None)之后只能out.show()和out.save()，无法返回预测结果图片。

解决方法

import cv2
import torch
from super_gradients.training import models

device = torch.device("cuda:0") if torch.cuda.is_available() else torch.device("cpu")
# yolo_nas_m,yolo_nas_l
model = models.get("yolo_nas_s", pretrained_weights="coco").to(device)
out = model.predict("camera01.png", conf=0.6)
# 关键在这
sigle_image_out = out._images_prediction_lst[0]
image = sigle_image_out.draw()
cv2.imshow('image',image)
cv2.waitKey()

原理

在out = model.predict(“camera01.png”, conf=0.6)处打断点，
debug，进入到predict函数里:

def predict(
    self,
    images: ImageSource,
    iou: Optional[float] = None,
    conf: Optional[float] = None,
    batch_size: int = 32,
    fuse_model: bool = True,
) -> ImagesDetectionPrediction:
    """Predict an image or a list of images.

    :param images:      Images to predict.
    :param iou:         (Optional) IoU threshold for the nms algorithm. If None, the default value associated to the training is used.
    :param conf:        (Optional) Below the confidence threshold, prediction are discarded.
                        If None, the default value associated to the training is used.
    :param batch_size:  Maximum number of images to process at the same time.
    :param fuse_model:  If True, create a copy of the model, and fuse some of its layers to increase performance. This increases memory usage.
    """
    pipeline = self._get_pipeline(iou=iou, conf=conf, fuse_model=fuse_model)
    return pipeline(images, batch_size=batch_size)  # type: ignore

接着debug有函数的地方就进去，到最后发现，out是ImagesDetectionPrediction类
ImagesDetectionPrediction类的属性是_images_prediction_lst: List[ImageDetectionPrediction]

里面有多个ImageDetectionPrediction类。
注意ImagesDetectionPrediction和ImageDetectionPrediction，一个是处理多个图片，一个是单个图片。其中ImageDetectionPrediction类有个draw方法，该方法画出了预测框并返回画出了预测框的结果。

所以如下两句代码，成功获取到了预测结果图片。
sigle_image_out = out._images_prediction_lst[0]
image = sigle_image_out.draw()

ImagesDetectionPrediction和ImageDetectionPrediction源码如下:

@dataclass
class ImagesDetectionPrediction(ImagesPredictions):
    """Object wrapping the list of image detection predictions.

    :attr _images_prediction_lst:  List of the predictions results
    """

    _images_prediction_lst: List[ImageDetectionPrediction]

    def show(self, box_thickness: int = 2, show_confidence: bool = True, color_mapping: Optional[List[Tuple[int, int, int]]] = None) -> None:
        """Display the predicted bboxes on the images.

        :param box_thickness:   Thickness of bounding boxes.
        :param show_confidence: Whether to show confidence scores on the image.
        :param color_mapping:   List of tuples representing the colors for each class.
                                Default is None, which generates a default color mapping based on the number of class names.
        """
        for prediction in self._images_prediction_lst:
            prediction.show(box_thickness=box_thickness, show_confidence=show_confidence, color_mapping=color_mapping)

    def save(
        self, output_folder: str, box_thickness: int = 2, show_confidence: bool = True, color_mapping: Optional[List[Tuple[int, int, int]]] = None
    ) -> None:
        """Save the predicted bboxes on the images.

        :param output_folder:     Folder path, where the images will be saved.
        :param box_thickness:   Thickness of bounding boxes.
        :param show_confidence: Whether to show confidence scores on the image.
        :param color_mapping:   List of tuples representing the colors for each class.
                                Default is None, which generates a default color mapping based on the number of class names.
        """
        if output_folder:
            os.makedirs(output_folder, exist_ok=True)

        for i, prediction in enumerate(self._images_prediction_lst):
            image_output_path = os.path.join(output_folder, f"pred_{i}.jpg")
            prediction.save(output_path=image_output_path, box_thickness=box_thickness, show_confidence=show_confidence, color_mapping=color_mapping)

_images_prediction_lst: List[ImageDetectionPrediction]

@dataclass
class ImageDetectionPrediction(ImagePrediction):
    """Object wrapping an image and a detection model's prediction.

    :attr image:        Input image
    :attr predictions:  Predictions of the model
    :attr class_names:  List of the class names to predict
    """

    image: np.ndarray
    prediction: DetectionPrediction
    class_names: List[str]

    def draw(self, box_thickness: int = 2, show_confidence: bool = True, color_mapping: Optional[List[Tuple[int, int, int]]] = None) -> np.ndarray:
        """Draw the predicted bboxes on the image.

        :param box_thickness:   Thickness of bounding boxes.
        :param show_confidence: Whether to show confidence scores on the image.
        :param color_mapping:   List of tuples representing the colors for each class.
                                Default is None, which generates a default color mapping based on the number of class names.
        :return:                Image with predicted bboxes. Note that this does not modify the original image.
        """
        image = self.image.copy()
        color_mapping = color_mapping or generate_color_mapping(len(self.class_names))

        for pred_i in np.argsort(self.prediction.confidence):
            class_id = int(self.prediction.labels[pred_i])
            score = "" if not show_confidence else str(round(self.prediction.confidence[pred_i], 2))

            image = draw_bbox(
                image=image,
                title=f"{self.class_names[class_id]} {score}",
                color=color_mapping[class_id],
                box_thickness=box_thickness,
                x1=int(self.prediction.bboxes_xyxy[pred_i, 0]),
                y1=int(self.prediction.bboxes_xyxy[pred_i, 1]),
                x2=int(self.prediction.bboxes_xyxy[pred_i, 2]),
                y2=int(self.prediction.bboxes_xyxy[pred_i, 3]),
            )

        return image

    def show(self, box_thickness: int = 2, show_confidence: bool = True, color_mapping: Optional[List[Tuple[int, int, int]]] = None) -> None:
        """Display the image with predicted bboxes.

        :param box_thickness:   Thickness of bounding boxes.
        :param show_confidence: Whether to show confidence scores on the image.
        :param color_mapping:   List of tuples representing the colors for each class.
                                Default is None, which generates a default color mapping based on the number of class names.
        """
        image = self.draw(box_thickness=box_thickness, show_confidence=show_confidence, color_mapping=color_mapping)
        show_image(image)

    def save(self, output_path: str, box_thickness: int = 2, show_confidence: bool = True, color_mapping: Optional[List[Tuple[int, int, int]]] = None) -> None:
        """Save the predicted bboxes on the images.

        :param output_path:     Path to the output video file.
        :param box_thickness:   Thickness of bounding boxes.
        :param show_confidence: Whether to show confidence scores on the image.
        :param color_mapping:   List of tuples representing the colors for each class.
                                Default is None, which generates a default color mapping based on the number of class names.
        """
        image = self.draw(box_thickness=box_thickness, show_confidence=show_confidence, color_mapping=color_mapping)
        save_image(image=image, path=output_path)