Add yolov8 to SAHI

[NguyenTheAn]

Add Yolov8DetectionModel class to infer Yolov8 with SAHI

[fcakyon]

@NguyenTheAn thanks a lot!

Can you please reformat your code following the steps in https://github.com/obss/sahi#contributing ?

And can you also add some tests in a file named test_yolov8model.py? You can take the yolov5 tests as reference: https://github.com/obss/sahi/blob/main/tests/test_yolov5model.py

[NguyenTheAn]

Yes, I will do that

[fcakyon]

All tests pass, thank you!

One final request: Would you mind adding a demo notebook for yolov8 as https://github.com/obss/sahi/blob/main/demo/inference_for_yolov5.ipynb

[NguyenTheAn]

yes, I added it

[mayrajeo]

Correct me if I'm wrong, but I think that perform_inference should convert the image to BGR before predicting. My reasoning is that when we pass numpy array or PIL image to the model for inference, YOLOv8 uses LoadPilAndNumpy for processing them. This class has functions

    @staticmethod
    def _single_check(im):
        assert isinstance(im, (Image.Image, np.ndarray)), f'Expected PIL/np.ndarray image type, but got {type(im)}'
        if isinstance(im, Image.Image):
            if im.mode != 'RGB':
                im = im.convert('RGB')
            im = np.asarray(im)[:, :, ::-1]
            im = np.ascontiguousarray(im)  # contiguous
        return im
        
    def _single_preprocess(self, im, auto):
        if self.transforms:
            im = self.transforms(im)  # transforms
        else:
            im = LetterBox(self.imgsz, auto=auto, stride=self.stride)(image=im)
            im = im.transpose((2, 0, 1))[::-1]  # HWC to CHW, BGR to RGB
            im = np.ascontiguousarray(im)  # contiguous
        return im

First, the image is checked with _single_check which converts the image to BGR only if its Image.Image. Then, before the model performs inference, _single_preprocess converts it from BGR to RGB unless there are transforms to apply (default=None). However, since im here is a numpy array with channel ordering RGB, _single_preprocess converts it to BGR.

Example notebook: https://nbviewer.org/gist/mayrajeo/033e842b7593e58135c7694944905937