def forward(
        self,
        pixel_values: Optional[torch.Tensor] = None,
        output_attentions: Optional[bool] = None,
        output_hidden_states: Optional[bool] = None,
        labels: Optional[torch.Tensor] = None,
        return_dict: Optional[bool] = None,
    ):
        """
        labels (`torch.LongTensor` of shape `(batch_size, height, width)`, *optional*):
            Ground truth image matting for computing the loss.

        Returns:

        Examples:

        ```python
        >>> from transformers import VitMatteImageProcessor, VitMatteForImageMatting
        >>> import torch
        >>> from PIL import Image
        >>> from huggingface_hub import hf_hub_download

        >>> processor = VitMatteImageProcessor.from_pretrained("hustvl/vitmatte-small-composition-1k")
        >>> model = VitMatteForImageMatting.from_pretrained("hustvl/vitmatte-small-composition-1k")

        >>> filepath = hf_hub_download(
        ...     repo_id="hf-internal-testing/image-matting-fixtures", filename="image.png", repo_type="dataset"
        ... )
        >>> image = Image.open(filepath).convert("RGB")
        >>> filepath = hf_hub_download(
        ...     repo_id="hf-internal-testing/image-matting-fixtures", filename="trimap.png", repo_type="dataset"
        ... )
        >>> trimap = Image.open(filepath).convert("L")

        >>> # prepare image + trimap for the model
        >>> inputs = processor(images=image, trimaps=trimap, return_tensors="pt")

        >>> with torch.no_grad():
        ...     alphas = model(**inputs).alphas
        >>> print(alphas.shape)
        torch.Size([1, 1, 640, 960])
        ```"""
        return_dict = return_dict if return_dict is not None else self.config.use_return_dict
        output_hidden_states = (
            output_hidden_states if output_hidden_states is not None else self.config.output_hidden_states
        )
        output_attentions = output_attentions if output_attentions is not None else self.config.output_attentions

        outputs = self.backbone.forward_with_filtered_kwargs(
            pixel_values, output_hidden_states=output_hidden_states, output_attentions=output_attentions
        )

        features = outputs.feature_maps[-1]
        alphas = self.decoder(features, pixel_values)

        loss = None
        if labels is not None:
            raise NotImplementedError("Training is not yet supported")

        if not return_dict:
            output = (alphas,) + outputs[1:]
            return ((loss,) + output) if loss is not None else output

        return ImageMattingOutput(
            loss=loss,
            alphas=alphas,
            hidden_states=outputs.hidden_states,
            attentions=outputs.attentions,
        )

        labels (`torch.LongTensor` of shape `(batch_size, height, width)`, *optional*):
            Ground truth image matting for computing the loss.

        Returns:

        Examples:

        ```python
        >>> from transformers import VitMatteImageProcessor, VitMatteForImageMatting
        >>> import torch
        >>> from PIL import Image
        >>> from huggingface_hub import hf_hub_download

        >>> processor = VitMatteImageProcessor.from_pretrained("hustvl/vitmatte-small-composition-1k")
        >>> model = VitMatteForImageMatting.from_pretrained("hustvl/vitmatte-small-composition-1k")

        >>> filepath = hf_hub_download(
        ...     repo_id="hf-internal-testing/image-matting-fixtures", filename="image.png", repo_type="dataset"
        ... )
        >>> image = Image.open(filepath).convert("RGB")
        >>> filepath = hf_hub_download(
        ...     repo_id="hf-internal-testing/image-matting-fixtures", filename="trimap.png", repo_type="dataset"
        ... )
        >>> trimap = Image.open(filepath).convert("L")

        >>> # prepare image + trimap for the model
        >>> inputs = processor(images=image, trimaps=trimap, return_tensors="pt")

        >>> with torch.no_grad():
        ...     alphas = model(**inputs).alphas
        >>> print(alphas.shape)
        torch.Size([1, 1, 640, 960])
        ```
dpkd/transformers/src/transformers/models/vitmatte/modeling_vitmatte.py