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from typing import List, Union
import datasets
import numpy as np
import torch
import torchvision.transforms as T
from PIL import Image
from tqdm.auto import tqdm
from transformers import AutoFeatureExtractor, AutoModel
seed = 42
hash_size = 8
hidden_dim = 768 # ViT-base
np.random.seed(seed)
# Device.
device = "cuda" if torch.cuda.is_available() else "cpu"
# Load model for computing embeddings..
model_ckpt = "gjuggler/swin-tiny-patch4-window7-224-finetuned-birds"
extractor = AutoFeatureExtractor.from_pretrained(model_ckpt)
# Data transformation chain.
transformation_chain = T.Compose(
[
# We first resize the input image to 256x256 and then we take center crop.
T.Resize(224),
T.CenterCrop(extractor.size["height"]),
T.ToTensor(),
T.Normalize(mean=extractor.image_mean, std=extractor.image_std),
]
)
# Define random vectors to project with.
random_vectors = np.random.randn(hash_size, hidden_dim).T
def hash_func(embedding, random_vectors=random_vectors):
"""Randomly projects the embeddings and then computes bit-wise hashes."""
if not isinstance(embedding, np.ndarray):
embedding = np.array(embedding)
if len(embedding.shape) < 2:
embedding = np.expand_dims(embedding, 0)
# Random projection.
bools = np.dot(embedding, random_vectors) > 0
return [bool2int(bool_vec) for bool_vec in bools]
def bool2int(x):
y = 0
for i, j in enumerate(x):
if j:
y += 1 << i
return y
def compute_hash(model: Union[torch.nn.Module, str]):
"""Computes hash on a given dataset."""
device = model.device
def pp(example_batch):
# Prepare the input images for the model.
image_batch = example_batch["image"]
image_batch_transformed = torch.stack(
[transformation_chain(image) for image in image_batch]
)
new_batch = {"pixel_values": image_batch_transformed.to(device)}
# Compute embeddings and pool them i.e., take the representations from the [CLS]
# token.
with torch.no_grad():
embeddings = model(**new_batch).last_hidden_state[:, 0].cpu().numpy()
# Compute hashes for the batch of images.
hashes = [hash_func(embeddings[i]) for i in range(len(embeddings))]
example_batch["hashes"] = hashes
return example_batch
return pp
class Table:
def __init__(self, hash_size: int):
self.table = {}
self.hash_size = hash_size
def add(self, id: int, hashes: List[int], label: int):
# Create a unique indentifier.
entry = {"id_label": str(id) + "_" + str(label)}
# Add the hash values to the current table.
for h in hashes:
if h in self.table:
self.table[h].append(entry)
else:
self.table[h] = [entry]
def query(self, hashes: List[int]):
results = []
# Loop over the query hashes and determine if they exist in
# the current table.
for h in hashes:
if h in self.table:
results.extend(self.table[h])
return results
class LSH:
def __init__(self, hash_size, num_tables):
self.num_tables = num_tables
self.tables = []
for i in range(self.num_tables):
self.tables.append(Table(hash_size))
def add(self, id: int, hash: List[int], label: int):
for table in self.tables:
table.add(id, hash, label)
def query(self, hashes: List[int]):
results = []
for table in self.tables:
results.extend(table.query(hashes))
return results
class BuildLSHTable:
def __init__(
self,
model: Union[torch.nn.Module, None],
batch_size: int = 48,
hash_size: int = hash_size,
dim: int = hidden_dim,
num_tables: int = 10,
):
self.hash_size = hash_size
self.dim = dim
self.num_tables = num_tables
self.lsh = LSH(self.hash_size, self.num_tables)
self.batch_size = batch_size
self.hash_fn = compute_hash(model.to(device))
def build(self, ds: datasets.DatasetDict):
dataset_hashed = ds.map(self.hash_fn, batched=True, batch_size=self.batch_size)
for id in tqdm(range(len(dataset_hashed))):
hash, label = dataset_hashed[id]["hashes"], dataset_hashed[id]["labels"]
self.lsh.add(id, hash, label)
def query(self, image, verbose=True):
if isinstance(image, str):
image = Image.open(image).convert("RGB")
# Compute the hashes of the query image and fetch the results.
example_batch = dict(image=[image])
hashes = self.hash_fn(example_batch)["hashes"][0]
results = self.lsh.query(hashes)
if verbose:
print("Matches:", len(results))
# Calculate Jaccard index to quantify the similarity.
counts = {}
for r in results:
if r["id_label"] in counts:
counts[r["id_label"]] += 1
else:
counts[r["id_label"]] = 1
for k in counts:
counts[k] = float(counts[k]) / self.dim
return counts
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