examples/YOLOv8-Segmentation-ONNXRuntime-Python/main.py

# Ultralytics YOLO 🚀, AGPL-3.0 license

import argparse

import cv2
import numpy as np
import onnxruntime as ort

from ultralytics.utils import ASSETS, yaml_load
from ultralytics.utils.checks import check_yaml
from ultralytics.utils.plotting import Colors


class YOLOv8Seg:
    """YOLOv8 segmentation model."""

    def __init__(self, onnx_model):
        """
        Initialization.

        Args:
            onnx_model (str): Path to the ONNX model.
        """
        # Build Ort session
        self.session = ort.InferenceSession(
            onnx_model,
            providers=["CUDAExecutionProvider", "CPUExecutionProvider"]
            if ort.get_device() == "GPU"
            else ["CPUExecutionProvider"],
        )

        # Numpy dtype: support both FP32 and FP16 onnx model
        self.ndtype = np.half if self.session.get_inputs()[0].type == "tensor(float16)" else np.single

        # Get model width and height(YOLOv8-seg only has one input)
        self.model_height, self.model_width = [x.shape for x in self.session.get_inputs()][0][-2:]

        # Load COCO class names
        self.classes = yaml_load(check_yaml("coco8.yaml"))["names"]

        # Create color palette
        self.color_palette = Colors()

    def __call__(self, im0, conf_threshold=0.4, iou_threshold=0.45, nm=32):
        """
        The whole pipeline: pre-process -> inference -> post-process.

        Args:
            im0 (Numpy.ndarray): original input image.
            conf_threshold (float): confidence threshold for filtering predictions.
            iou_threshold (float): iou threshold for NMS.
            nm (int): the number of masks.

        Returns:
            boxes (List): list of bounding boxes.
            segments (List): list of segments.
            masks (np.ndarray): [N, H, W], output masks.
        """
        # Pre-process
        im, ratio, (pad_w, pad_h) = self.preprocess(im0)

        # Ort inference
        preds = self.session.run(None, {self.session.get_inputs()[0].name: im})

        # Post-process
        boxes, segments, masks = self.postprocess(
            preds,
            im0=im0,
            ratio=ratio,
            pad_w=pad_w,
            pad_h=pad_h,
            conf_threshold=conf_threshold,
            iou_threshold=iou_threshold,
            nm=nm,
        )
        return boxes, segments, masks

    def preprocess(self, img):
        """
        Pre-processes the input image.

        Args:
            img (Numpy.ndarray): image about to be processed.

        Returns:
            img_process (Numpy.ndarray): image preprocessed for inference.
            ratio (tuple): width, height ratios in letterbox.
            pad_w (float): width padding in letterbox.
            pad_h (float): height padding in letterbox.
        """
        # Resize and pad input image using letterbox() (Borrowed from Ultralytics)
        shape = img.shape[:2]  # original image shape
        new_shape = (self.model_height, self.model_width)
        r = min(new_shape[0] / shape[0], new_shape[1] / shape[1])
        ratio = r, r
        new_unpad = int(round(shape[1] * r)), int(round(shape[0] * r))
        pad_w, pad_h = (new_shape[1] - new_unpad[0]) / 2, (new_shape[0] - new_unpad[1]) / 2  # wh padding
        if shape[::-1] != new_unpad:  # resize
            img = cv2.resize(img, new_unpad, interpolation=cv2.INTER_LINEAR)
        top, bottom = int(round(pad_h - 0.1)), int(round(pad_h + 0.1))
        left, right = int(round(pad_w - 0.1)), int(round(pad_w + 0.1))
        img = cv2.copyMakeBorder(img, top, bottom, left, right, cv2.BORDER_CONSTANT, value=(114, 114, 114))

        # Transforms: HWC to CHW -> BGR to RGB -> div(255) -> contiguous -> add axis(optional)
        img = np.ascontiguousarray(np.einsum("HWC->CHW", img)[::-1], dtype=self.ndtype) / 255.0
        img_process = img[None] if len(img.shape) == 3 else img
        return img_process, ratio, (pad_w, pad_h)

    def postprocess(self, preds, im0, ratio, pad_w, pad_h, conf_threshold, iou_threshold, nm=32):
        """
        Post-process the prediction.

        Args:
            preds (Numpy.ndarray): predictions come from ort.session.run().
            im0 (Numpy.ndarray): [h, w, c] original input image.
            ratio (tuple): width, height ratios in letterbox.
            pad_w (float): width padding in letterbox.
            pad_h (float): height padding in letterbox.
            conf_threshold (float): conf threshold.
            iou_threshold (float): iou threshold.
            nm (int): the number of masks.

        Returns:
            boxes (List): list of bounding boxes.
            segments (List): list of segments.
            masks (np.ndarray): [N, H, W], output masks.
        """
        x, protos = preds[0], preds[1]  # Two outputs: predictions and protos

        # Transpose dim 1: (Batch_size, xywh_conf_cls_nm, Num_anchors) -> (Batch_size, Num_anchors, xywh_conf_cls_nm)
        x = np.einsum("bcn->bnc", x)

        # Predictions filtering by conf-threshold
        x = x[np.amax(x[..., 4:-nm], axis=-1) > conf_threshold]

        # Create a new matrix which merge these(box, score, cls, nm) into one
        # For more details about `numpy.c_()`: https://numpy.org/doc/1.26/reference/generated/numpy.c_.html
        x = np.c_[x[..., :4], np.amax(x[..., 4:-nm], axis=-1), np.argmax(x[..., 4:-nm], axis=-1), x[..., -nm:]]

        # NMS filtering
        x = x[cv2.dnn.NMSBoxes(x[:, :4], x[:, 4], conf_threshold, iou_threshold)]

        # Decode and return
        if len(x) > 0:
            # Bounding boxes format change: cxcywh -> xyxy
            x[..., [0, 1]] -= x[..., [2, 3]] / 2
            x[..., [2, 3]] += x[..., [0, 1]]

            # Rescales bounding boxes from model shape(model_height, model_width) to the shape of original image
            x[..., :4] -= [pad_w, pad_h, pad_w, pad_h]
            x[..., :4] /= min(ratio)

            # Bounding boxes boundary clamp
            x[..., [0, 2]] = x[:, [0, 2]].clip(0, im0.shape[1])
            x[..., [1, 3]] = x[:, [1, 3]].clip(0, im0.shape[0])

            # Process masks
            masks = self.process_mask(protos[0], x[:, 6:], x[:, :4], im0.shape)

            # Masks -> Segments(contours)
            segments = self.masks2segments(masks)
            return x[..., :6], segments, masks  # boxes, segments, masks
        else:
            return [], [], []

    @staticmethod
    def masks2segments(masks):
        """
        Takes a list of masks(n,h,w) and returns a list of segments(n,xy), from
        https://github.com/ultralytics/ultralytics/blob/main/ultralytics/utils/ops.py.

        Args:
            masks (numpy.ndarray): the output of the model, which is a tensor of shape (batch_size, 160, 160).

        Returns:
            segments (List): list of segment masks.
        """
        segments = []
        for x in masks.astype("uint8"):
            c = cv2.findContours(x, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)[0]  # CHAIN_APPROX_SIMPLE
            if c:
                c = np.array(c[np.array([len(x) for x in c]).argmax()]).reshape(-1, 2)
            else:
                c = np.zeros((0, 2))  # no segments found
            segments.append(c.astype("float32"))
        return segments

    @staticmethod
    def crop_mask(masks, boxes):
        """
        Takes a mask and a bounding box, and returns a mask that is cropped to the bounding box, from
        https://github.com/ultralytics/ultralytics/blob/main/ultralytics/utils/ops.py.

        Args:
            masks (Numpy.ndarray): [n, h, w] tensor of masks.
            boxes (Numpy.ndarray): [n, 4] tensor of bbox coordinates in relative point form.

        Returns:
            (Numpy.ndarray): The masks are being cropped to the bounding box.
        """
        n, h, w = masks.shape
        x1, y1, x2, y2 = np.split(boxes[:, :, None], 4, 1)
        r = np.arange(w, dtype=x1.dtype)[None, None, :]
        c = np.arange(h, dtype=x1.dtype)[None, :, None]
        return masks * ((r >= x1) * (r < x2) * (c >= y1) * (c < y2))

    def process_mask(self, protos, masks_in, bboxes, im0_shape):
        """
        Takes the output of the mask head, and applies the mask to the bounding boxes. This produces masks of higher
        quality but is slower, from https://github.com/ultralytics/ultralytics/blob/main/ultralytics/utils/ops.py.

        Args:
            protos (numpy.ndarray): [mask_dim, mask_h, mask_w].
            masks_in (numpy.ndarray): [n, mask_dim], n is number of masks after nms.
            bboxes (numpy.ndarray): bboxes re-scaled to original image shape.
            im0_shape (tuple): the size of the input image (h,w,c).

        Returns:
            (numpy.ndarray): The upsampled masks.
        """
        c, mh, mw = protos.shape
        masks = np.matmul(masks_in, protos.reshape((c, -1))).reshape((-1, mh, mw)).transpose(1, 2, 0)  # HWN
        masks = np.ascontiguousarray(masks)
        masks = self.scale_mask(masks, im0_shape)  # re-scale mask from P3 shape to original input image shape
        masks = np.einsum("HWN -> NHW", masks)  # HWN -> NHW
        masks = self.crop_mask(masks, bboxes)
        return np.greater(masks, 0.5)

    @staticmethod
    def scale_mask(masks, im0_shape, ratio_pad=None):
        """
        Takes a mask, and resizes it to the original image size, from
        https://github.com/ultralytics/ultralytics/blob/main/ultralytics/utils/ops.py.

        Args:
            masks (np.ndarray): resized and padded masks/images, [h, w, num]/[h, w, 3].
            im0_shape (tuple): the original image shape.
            ratio_pad (tuple): the ratio of the padding to the original image.

        Returns:
            masks (np.ndarray): The masks that are being returned.
        """
        im1_shape = masks.shape[:2]
        if ratio_pad is None:  # calculate from im0_shape
            gain = min(im1_shape[0] / im0_shape[0], im1_shape[1] / im0_shape[1])  # gain  = old / new
            pad = (im1_shape[1] - im0_shape[1] * gain) / 2, (im1_shape[0] - im0_shape[0] * gain) / 2  # wh padding
        else:
            pad = ratio_pad[1]

        # Calculate tlbr of mask
        top, left = int(round(pad[1] - 0.1)), int(round(pad[0] - 0.1))  # y, x
        bottom, right = int(round(im1_shape[0] - pad[1] + 0.1)), int(round(im1_shape[1] - pad[0] + 0.1))
        if len(masks.shape) < 2:
            raise ValueError(f'"len of masks shape" should be 2 or 3, but got {len(masks.shape)}')
        masks = masks[top:bottom, left:right]
        masks = cv2.resize(
            masks, (im0_shape[1], im0_shape[0]), interpolation=cv2.INTER_LINEAR
        )  # INTER_CUBIC would be better
        if len(masks.shape) == 2:
            masks = masks[:, :, None]
        return masks

    def draw_and_visualize(self, im, bboxes, segments, vis=False, save=True):
        """
        Draw and visualize results.

        Args:
            im (np.ndarray): original image, shape [h, w, c].
            bboxes (numpy.ndarray): [n, 4], n is number of bboxes.
            segments (List): list of segment masks.
            vis (bool): imshow using OpenCV.
            save (bool): save image annotated.

        Returns:
            None
        """
        # Draw rectangles and polygons
        im_canvas = im.copy()
        for (*box, conf, cls_), segment in zip(bboxes, segments):
            # draw contour and fill mask
            cv2.polylines(im, np.int32([segment]), True, (255, 255, 255), 2)  # white borderline
            cv2.fillPoly(im_canvas, np.int32([segment]), self.color_palette(int(cls_), bgr=True))

            # draw bbox rectangle
            cv2.rectangle(
                im,
                (int(box[0]), int(box[1])),
                (int(box[2]), int(box[3])),
                self.color_palette(int(cls_), bgr=True),
                1,
                cv2.LINE_AA,
            )
            cv2.putText(
                im,
                f"{self.classes[cls_]}: {conf:.3f}",
                (int(box[0]), int(box[1] - 9)),
                cv2.FONT_HERSHEY_SIMPLEX,
                0.7,
                self.color_palette(int(cls_), bgr=True),
                2,
                cv2.LINE_AA,
            )

        # Mix image
        im = cv2.addWeighted(im_canvas, 0.3, im, 0.7, 0)

        # Show image
        if vis:
            cv2.imshow("demo", im)
            cv2.waitKey(0)
            cv2.destroyAllWindows()

        # Save image
        if save:
            cv2.imwrite("demo.jpg", im)


if __name__ == "__main__":
    # Create an argument parser to handle command-line arguments
    parser = argparse.ArgumentParser()
    parser.add_argument("--model", type=str, required=True, help="Path to ONNX model")
    parser.add_argument("--source", type=str, default=str(ASSETS / "bus.jpg"), help="Path to input image")
    parser.add_argument("--conf", type=float, default=0.25, help="Confidence threshold")
    parser.add_argument("--iou", type=float, default=0.45, help="NMS IoU threshold")
    args = parser.parse_args()

    # Build model
    model = YOLOv8Seg(args.model)

    # Read image by OpenCV
    img = cv2.imread(args.source)

    # Inference
    boxes, segments, _ = model(img, conf_threshold=args.conf, iou_threshold=args.iou)

    # Draw bboxes and polygons
    if len(boxes) > 0:
        model.draw_and_visualize(img, boxes, segments, vis=False, save=True)