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| # 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 numpy as np | |
| import torch | |
| from torch import nn | |
| from typing import Any, Optional, Tuple, Type | |
| from .common import LayerNorm2d | |
| class PromptEncoder(nn.Module): | |
| def __init__( | |
| self, | |
| embed_dim: int, | |
| image_embedding_size: Tuple[int, int], | |
| input_image_size: Tuple[int, int], | |
| mask_in_chans: int, | |
| activation: Type[nn.Module] = nn.GELU, | |
| ) -> None: | |
| """ | |
| Encodes prompts for input to SAM's mask decoder. | |
| Arguments: | |
| embed_dim (int): The prompts' embedding dimension | |
| image_embedding_size (tuple(int, int)): The spatial size of the | |
| image embedding, as (H, W). | |
| input_image_size (int): The padded size of the image as input | |
| to the image encoder, as (H, W). | |
| mask_in_chans (int): The number of hidden channels used for | |
| encoding input masks. | |
| activation (nn.Module): The activation to use when encoding | |
| input masks. | |
| """ | |
| super().__init__() | |
| self.embed_dim = embed_dim | |
| self.input_image_size = input_image_size | |
| self.image_embedding_size = image_embedding_size | |
| self.pe_layer = PositionEmbeddingRandom(embed_dim // 2) | |
| self.num_point_embeddings: int = 4 # pos/neg point + 2 box corners | |
| point_embeddings = [nn.Embedding(1, embed_dim) for i in range(self.num_point_embeddings)] | |
| self.point_embeddings = nn.ModuleList(point_embeddings) | |
| self.not_a_point_embed = nn.Embedding(1, embed_dim) | |
| self.mask_input_size = (4 * image_embedding_size[0], 4 * image_embedding_size[1]) | |
| self.mask_downscaling = nn.Sequential( | |
| nn.Conv2d(1, mask_in_chans // 4, kernel_size=2, stride=2), | |
| LayerNorm2d(mask_in_chans // 4), | |
| activation(), | |
| nn.Conv2d(mask_in_chans // 4, mask_in_chans, kernel_size=2, stride=2), | |
| LayerNorm2d(mask_in_chans), | |
| activation(), | |
| nn.Conv2d(mask_in_chans, embed_dim, kernel_size=1), | |
| ) | |
| self.no_mask_embed = nn.Embedding(1, embed_dim) | |
| def get_dense_pe(self) -> torch.Tensor: | |
| """ | |
| Returns the positional encoding used to encode point prompts, | |
| applied to a dense set of points the shape of the image encoding. | |
| Returns: | |
| torch.Tensor: Positional encoding with shape | |
| 1x(embed_dim)x(embedding_h)x(embedding_w) | |
| """ | |
| return self.pe_layer(self.image_embedding_size).unsqueeze(0) | |
| def _embed_points( | |
| self, | |
| points: torch.Tensor, | |
| labels: torch.Tensor, | |
| pad: bool, | |
| ) -> torch.Tensor: | |
| """Embeds point prompts.""" | |
| points = points + 0.5 # Shift to center of pixel | |
| if pad: | |
| padding_point = torch.zeros((points.shape[0], 1, 2), device=points.device) | |
| padding_label = -torch.ones((labels.shape[0], 1), device=labels.device) | |
| points = torch.cat([points, padding_point], dim=1) | |
| labels = torch.cat([labels, padding_label], dim=1) | |
| point_embedding = self.pe_layer.forward_with_coords(points, self.input_image_size) | |
| point_embedding[labels == -1] = 0.0 | |
| point_embedding[labels == -1] += self.not_a_point_embed.weight | |
| point_embedding[labels == 0] += self.point_embeddings[0].weight | |
| point_embedding[labels == 1] += self.point_embeddings[1].weight | |
| return point_embedding | |
| def _embed_boxes(self, boxes: torch.Tensor) -> torch.Tensor: | |
| """Embeds box prompts.""" | |
| boxes = boxes + 0.5 # Shift to center of pixel | |
| coords = boxes.reshape(-1, 2, 2) | |
| corner_embedding = self.pe_layer.forward_with_coords(coords, self.input_image_size) | |
| corner_embedding[:, 0, :] += self.point_embeddings[2].weight | |
| corner_embedding[:, 1, :] += self.point_embeddings[3].weight | |
| return corner_embedding | |
| def _embed_masks(self, masks: torch.Tensor) -> torch.Tensor: | |
| """Embeds mask inputs.""" | |
| mask_embedding = self.mask_downscaling(masks) | |
| return mask_embedding | |
| def _get_batch_size( | |
| self, | |
| points: Optional[Tuple[torch.Tensor, torch.Tensor]], | |
| boxes: Optional[torch.Tensor], | |
| masks: Optional[torch.Tensor], | |
| ) -> int: | |
| """ | |
| Gets the batch size of the output given the batch size of the input prompts. | |
| """ | |
| if points is not None: | |
| return points[0].shape[0] | |
| elif boxes is not None: | |
| return boxes.shape[0] | |
| elif masks is not None: | |
| return masks.shape[0] | |
| else: | |
| return 1 | |
| def _get_device(self) -> torch.device: | |
| return self.point_embeddings[0].weight.device | |
| def forward( | |
| self, | |
| points: Optional[Tuple[torch.Tensor, torch.Tensor]], | |
| boxes: Optional[torch.Tensor], | |
| masks: Optional[torch.Tensor], | |
| ) -> Tuple[torch.Tensor, torch.Tensor]: | |
| """ | |
| Embeds different types of prompts, returning both sparse and dense | |
| embeddings. | |
| Arguments: | |
| points (tuple(torch.Tensor, torch.Tensor) or none): point coordinates | |
| and labels to embed. | |
| boxes (torch.Tensor or none): boxes to embed | |
| masks (torch.Tensor or none): masks to embed | |
| Returns: | |
| torch.Tensor: sparse embeddings for the points and boxes, with shape | |
| BxNx(embed_dim), where N is determined by the number of input points | |
| and boxes. | |
| torch.Tensor: dense embeddings for the masks, in the shape | |
| Bx(embed_dim)x(embed_H)x(embed_W) | |
| """ | |
| bs = self._get_batch_size(points, boxes, masks) | |
| sparse_embeddings = torch.empty((bs, 0, self.embed_dim), device=self._get_device()) | |
| if points is not None: | |
| coords, labels = points | |
| point_embeddings = self._embed_points(coords, labels, pad=(boxes is None)) | |
| sparse_embeddings = torch.cat([sparse_embeddings, point_embeddings], dim=1) | |
| if boxes is not None: | |
| box_embeddings = self._embed_boxes(boxes) | |
| sparse_embeddings = torch.cat([sparse_embeddings, box_embeddings], dim=1) | |
| if masks is not None: | |
| dense_embeddings = self._embed_masks(masks) | |
| else: | |
| dense_embeddings = self.no_mask_embed.weight.reshape(1, -1, 1, 1).expand( | |
| bs, -1, self.image_embedding_size[0], self.image_embedding_size[1] | |
| ) | |
| return sparse_embeddings, dense_embeddings | |
| class PositionEmbeddingRandom(nn.Module): | |
| """ | |
| Positional encoding using random spatial frequencies. | |
| """ | |
| def __init__(self, num_pos_feats: int = 64, scale: Optional[float] = None) -> None: | |
| super().__init__() | |
| if scale is None or scale <= 0.0: | |
| scale = 1.0 | |
| self.register_buffer( | |
| "positional_encoding_gaussian_matrix", | |
| scale * torch.randn((2, num_pos_feats)), | |
| ) | |
| def _pe_encoding(self, coords: torch.Tensor) -> torch.Tensor: | |
| """Positionally encode points that are normalized to [0,1].""" | |
| # assuming coords are in [0, 1]^2 square and have d_1 x ... x d_n x 2 shape | |
| coords = 2 * coords - 1 | |
| coords = coords @ self.positional_encoding_gaussian_matrix | |
| coords = 2 * np.pi * coords | |
| # outputs d_1 x ... x d_n x C shape | |
| return torch.cat([torch.sin(coords), torch.cos(coords)], dim=-1) | |
| def forward(self, size: Tuple[int, int]) -> torch.Tensor: | |
| """Generate positional encoding for a grid of the specified size.""" | |
| h, w = size | |
| device: Any = self.positional_encoding_gaussian_matrix.device | |
| grid = torch.ones((h, w), device=device, dtype=torch.float32) | |
| y_embed = grid.cumsum(dim=0) - 0.5 | |
| x_embed = grid.cumsum(dim=1) - 0.5 | |
| y_embed = y_embed / h | |
| x_embed = x_embed / w | |
| pe = self._pe_encoding(torch.stack([x_embed, y_embed], dim=-1)) | |
| return pe.permute(2, 0, 1) # C x H x W | |
| def forward_with_coords( | |
| self, coords_input: torch.Tensor, image_size: Tuple[int, int] | |
| ) -> torch.Tensor: | |
| """Positionally encode points that are not normalized to [0,1].""" | |
| coords = coords_input.clone() | |
| coords[:, :, 0] = coords[:, :, 0] / image_size[1] | |
| coords[:, :, 1] = coords[:, :, 1] / image_size[0] | |
| return self._pe_encoding(coords.to(torch.float)) # B x N x C | |