sam2/utils/transforms.py

# Copyright (c) Meta Platforms, Inc. and affiliates.
# All rights reserved.

# This source code is licensed under the license found in the
# LICENSE file in the root directory of this source tree.

import torch
import torch.nn as nn
import torch.nn.functional as F
from torchvision.transforms import Normalize, Resize, ToTensor


class SAM2Transforms(nn.Module):
    def __init__(
        self, resolution, mask_threshold, max_hole_area=0.0, max_sprinkle_area=0.0
    ):
        """
        Transforms for SAM2.
        """
        super().__init__()
        self.resolution = resolution
        self.mask_threshold = mask_threshold
        self.max_hole_area = max_hole_area
        self.max_sprinkle_area = max_sprinkle_area
        self.mean = [0.485, 0.456, 0.406]
        self.std = [0.229, 0.224, 0.225]
        self.to_tensor = ToTensor()
        self.transforms = torch.jit.script(
            nn.Sequential(
                Resize((self.resolution, self.resolution)),
                Normalize(self.mean, self.std),
            )
        )

    def __call__(self, x):
        x = self.to_tensor(x)
        return self.transforms(x)

    def forward_batch(self, img_list):
        img_batch = [self.transforms(self.to_tensor(img)) for img in img_list]
        img_batch = torch.stack(img_batch, dim=0)
        return img_batch

    def transform_coords(
        self, coords: torch.Tensor, normalize=False, orig_hw=None
    ) -> torch.Tensor:
        """
        Expects a torch tensor with length 2 in the last dimension. The coordinates can be in absolute image or normalized coordinates,
        If the coords are in absolute image coordinates, normalize should be set to True and original image size is required.

        Returns
            Un-normalized coordinates in the range of [0, 1] which is expected by the SAM2 model.
        """
        if normalize:
            assert orig_hw is not None
            h, w = orig_hw
            coords = coords.clone()
            coords[..., 0] = coords[..., 0] / w
            coords[..., 1] = coords[..., 1] / h

        coords = coords * self.resolution  # unnormalize coords
        return coords

    def transform_boxes(
        self, boxes: torch.Tensor, normalize=False, orig_hw=None
    ) -> torch.Tensor:
        """
        Expects a tensor of shape Bx4. The coordinates can be in absolute image or normalized coordinates,
        if the coords are in absolute image coordinates, normalize should be set to True and original image size is required.
        """
        boxes = self.transform_coords(boxes.reshape(-1, 2, 2), normalize, orig_hw)
        return boxes

    def postprocess_masks(self, masks: torch.Tensor, orig_hw) -> torch.Tensor:
        """
        Perform PostProcessing on output masks.
        """
        from sam2.utils.misc import get_connected_components

        masks = masks.float()
        if self.max_hole_area > 0:
            # Holes are those connected components in background with area <= self.fill_hole_area
            # (background regions are those with mask scores <= self.mask_threshold)
            mask_flat = masks.flatten(0, 1).unsqueeze(1)  # flatten as 1-channel image
            labels, areas = get_connected_components(mask_flat <= self.mask_threshold)
            is_hole = (labels > 0) & (areas <= self.max_hole_area)
            is_hole = is_hole.reshape_as(masks)
            # We fill holes with a small positive mask score (10.0) to change them to foreground.
            masks = torch.where(is_hole, self.mask_threshold + 10.0, masks)

        if self.max_sprinkle_area > 0:
            labels, areas = get_connected_components(mask_flat > self.mask_threshold)
            is_hole = (labels > 0) & (areas <= self.max_sprinkle_area)
            is_hole = is_hole.reshape_as(masks)
            # We fill holes with negative mask score (-10.0) to change them to background.
            masks = torch.where(is_hole, self.mask_threshold - 10.0, masks)

        masks = F.interpolate(masks, orig_hw, mode="bilinear", align_corners=False)
        return masks