huggingface--transformers/docs/source/en/model_doc/sam2.md

This model was contributed to Hugging Face Transformers on 2025-08-14.

SAM2

Overview

SAM2 (Segment Anything Model 2) was proposed in Segment Anything in Images and Videos by Nikhila Ravi, Valentin Gabeur, Yuan-Ting Hu, Ronghang Hu, Chaitanya Ryali, Tengyu Ma, Haitham Khedr, Roman Rädle, Chloe Rolland, Laura Gustafson, Eric Mintun, Junting Pan, Kalyan Vasudev Alwala, Nicolas Carion, Chao-Yuan Wu, Ross Girshick, Piotr Dollár, Christoph Feichtenhofer.

The model can be used to predict segmentation masks of any object of interest given an input image or video, and input points or bounding boxes.

The abstract from the paper is the following:

We present Segment Anything Model 2 (SAM 2), a foundation model towards solving promptable visual segmentation in images and videos. We build a data engine, which improves model and data via user interaction, to collect the largest video segmentation dataset to date. Our model is a simple transformer architecture with streaming memory for real-time video processing. SAM 2 trained on our data provides strong performance across a wide range of tasks. In video segmentation, we observe better accuracy, using 3x fewer interactions than prior approaches. In image segmentation, our model is more accurate and 6x faster than the Segment Anything Model (SAM). We believe that our data, model, and insights will serve as a significant milestone for video segmentation and related perception tasks. We are releasing a version of our model, the dataset and an interactive demo.

Tips:

• Batch & Video Support: SAM2 natively supports batch processing and seamless video segmentation, while original SAM is designed for static images and simpler one-image-at-a-time workflows.
• Accuracy & Generalization: SAM2 shows improved segmentation quality, robustness, and zero-shot generalization to new domains compared to the original SAM, especially with mixed prompts.

This model was contributed by sangbumchoi and yonigozlan. The original code can be found here.

Usage example

Automatic Mask Generation with Pipeline

SAM2 can be used for automatic mask generation to segment all objects in an image using the mask-generation pipeline:

from transformers import pipeline


generator = pipeline("mask-generation", model="facebook/sam2.1-hiera-large", device=0)
image_url = "https://huggingface.co/datasets/hf-internal-testing/sam2-fixtures/resolve/main/truck.jpg"
outputs = generator(image_url, points_per_batch=64)

len(outputs["masks"])  # Number of masks generated
39

Basic Image Segmentation

Single Point Click

You can segment objects by providing a single point click on the object you want to segment:

from transformers import Sam2Processor, Sam2Model
import torch
from PIL import Image
import requests


model = Sam2Model.from_pretrained("facebook/sam2.1-hiera-large", device_map="auto")
processor = Sam2Processor.from_pretrained("facebook/sam2.1-hiera-large")

image_url = "https://huggingface.co/datasets/hf-internal-testing/sam2-fixtures/resolve/main/truck.jpg"
raw_image = Image.open(requests.get(image_url, stream=True).raw).convert("RGB")

input_points = [[[[500, 375]]]]  # Single point click, 4 dimensions (image_dim, object_dim, point_per_object_dim, coordinates)
input_labels = [[[1]]]  # 1 for positive click, 0 for negative click, 3 dimensions (image_dim, object_dim, point_label)

inputs = processor(images=raw_image, input_points=input_points, input_labels=input_labels, return_tensors="pt").to(model.device)

with torch.no_grad():
    outputs = model(**inputs)

masks = processor.post_process_masks(outputs.pred_masks.cpu(), inputs["original_sizes"])[0]

# The model outputs multiple mask predictions ranked by quality score
print(f"Generated {masks.shape[1]} masks with shape {masks.shape}")
Generated 3 masks with shape torch.Size(1, 3, 1500, 2250)

Multiple Points for Refinement

You can provide multiple points to refine the segmentation:

# Add both positive and negative points to refine the mask
input_points = [[[[500, 375], [1125, 625]]]]  # Multiple points for refinement
input_labels = [[[1, 1]]]  # Both positive clicks

inputs = processor(images=raw_image, input_points=input_points, input_labels=input_labels, return_tensors="pt").to(model.device)

with torch.no_grad():
    outputs = model(**inputs)

masks = processor.post_process_masks(outputs.pred_masks.cpu(), inputs["original_sizes"])[0]

Bounding Box Input

SAM2 also supports bounding box inputs for segmentation:

# Define bounding box as [x_min, y_min, x_max, y_max]
input_boxes = [[[75, 275, 1725, 850]]]

inputs = processor(images=raw_image, input_boxes=input_boxes, return_tensors="pt").to(model.device)

with torch.no_grad():
    outputs = model(**inputs)

masks = processor.post_process_masks(outputs.pred_masks.cpu(), inputs["original_sizes"])[0]

Multiple Objects Segmentation

You can segment multiple objects simultaneously:

# Define points for two different objects
input_points = [[[[500, 375]], [[650, 750]]]]  # Points for two objects in same image
input_labels = [[[1], [1]]]  # Positive clicks for both objects

inputs = processor(images=raw_image, input_points=input_points, input_labels=input_labels, return_tensors="pt").to(model.device)

with torch.no_grad():
    outputs = model(**inputs, multimask_output=False)

# Each object gets its own mask
masks = processor.post_process_masks(outputs.pred_masks.cpu(), inputs["original_sizes"])[0]
print(f"Generated masks for {masks.shape[0]} objects")
Generated masks for 2 objects

Batch Inference

Batched Images

Process multiple images simultaneously for improved efficiency:

from transformers import Sam2Processor, Sam2Model
import torch
from PIL import Image
import requests


model = Sam2Model.from_pretrained("facebook/sam2.1-hiera-large", device_map="auto")
processor = Sam2Processor.from_pretrained("facebook/sam2.1-hiera-large")

# Load multiple images
image_urls = [
    "https://huggingface.co/datasets/hf-internal-testing/sam2-fixtures/resolve/main/truck.jpg",
    "https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/transformers/model_doc/dog-sam.png"
]
raw_images = [Image.open(requests.get(url, stream=True).raw).convert("RGB") for url in image_urls]

# Single point per image
input_points = [[[[500, 375]]], [[[770, 200]]]]  # One point for each image
input_labels = [[[1]], [[1]]]  # Positive clicks for both images

inputs = processor(images=raw_images, input_points=input_points, input_labels=input_labels, return_tensors="pt").to(model.device)

with torch.no_grad():
    outputs = model(**inputs, multimask_output=False)

# Post-process masks for each image
all_masks = processor.post_process_masks(outputs.pred_masks.cpu(), inputs["original_sizes"])
print(f"Processed {len(all_masks)} images, each with {all_masks[0].shape[0]} objects")
Processed 2 images, each with 1 objects

Batched Objects per Image

Segment multiple objects within each image using batch inference:

# Multiple objects per image - different numbers of objects per image
input_points = [
    [[[500, 375]], [[650, 750]]],  # Truck image: 2 objects
    [[[770, 200]]]  # Dog image: 1 object
]
input_labels = [
    [[1], [1]],  # Truck image: positive clicks for both objects
    [[1]]  # Dog image: positive click for the object
]

inputs = processor(images=raw_images, input_points=input_points, input_labels=input_labels, return_tensors="pt").to(model.device)

with torch.no_grad():
    outputs = model(**inputs, multimask_output=False)

all_masks = processor.post_process_masks(outputs.pred_masks.cpu(), inputs["original_sizes"])

Batched Images with Batched Objects and Multiple Points

Handle complex batch scenarios with multiple points per object:

# Add groceries image for more complex example
groceries_url = "https://huggingface.co/datasets/hf-internal-testing/sam2-fixtures/resolve/main/groceries.jpg"
groceries_image = Image.open(requests.get(groceries_url, stream=True).raw).convert("RGB")
raw_images = [raw_images[0], groceries_image]  # Use truck and groceries images

# Complex batching: multiple images, multiple objects, multiple points per object
input_points = [
    [[[500, 375]], [[650, 750]]],  # Truck image: 2 objects with 1 point each
    [[[400, 300]], [[630, 300], [550, 300]]]  # Groceries image: obj1 has 1 point, obj2 has 2 points
]
input_labels = [
    [[1], [1]],  # Truck image: positive clicks
    [[1], [1, 1]]  # Groceries image: positive clicks for refinement
]

inputs = processor(images=raw_images, input_points=input_points, input_labels=input_labels, return_tensors="pt").to(model.device)

with torch.no_grad():
    outputs = model(**inputs, multimask_output=False)

all_masks = processor.post_process_masks(outputs.pred_masks.cpu(), inputs["original_sizes"])

Batched Bounding Boxes

Process multiple images with bounding box inputs:

# Multiple bounding boxes per image (using truck and groceries images)
input_boxes = [
    [[75, 275, 1725, 850], [425, 600, 700, 875], [1375, 550, 1650, 800], [1240, 675, 1400, 750]],  # Truck image: 4 boxes
    [[450, 170, 520, 350], [350, 190, 450, 350], [500, 170, 580, 350], [580, 170, 640, 350]]  # Groceries image: 4 boxes
]

# Update images for this example
raw_images = [raw_images[0], groceries_image]  # truck and groceries

inputs = processor(images=raw_images, input_boxes=input_boxes, return_tensors="pt").to(model.device)

with torch.no_grad():
    outputs = model(**inputs, multimask_output=False)

all_masks = processor.post_process_masks(outputs.pred_masks.cpu(), inputs["original_sizes"])
print(f"Processed {len(input_boxes)} images with {len(input_boxes[0])} and {len(input_boxes[1])} boxes respectively")
Processed 2 images with 4 and 4 boxes respectively

Using Previous Masks as Input

SAM2 can use masks from previous predictions as input to refine segmentation:

# Get initial segmentation
input_points = [[[[500, 375]]]]
input_labels = [[[1]]]
inputs = processor(images=raw_image, input_points=input_points, input_labels=input_labels, return_tensors="pt").to(model.device)

with torch.no_grad():
    outputs = model(**inputs)

# Use the best mask as input for refinement
mask_input = outputs.pred_masks[:, :, torch.argmax(outputs.iou_scores.squeeze())]

# Add additional points with the mask input
new_input_points = [[[[500, 375], [450, 300]]]]
new_input_labels = [[[1, 1]]]
inputs = processor(
    input_points=new_input_points,
    input_labels=new_input_labels,
    original_sizes=inputs["original_sizes"],
    return_tensors="pt",
).to(model.device)

with torch.no_grad():
    refined_outputs = model(
        **inputs,
        input_masks=mask_input,
        image_embeddings=outputs.image_embeddings,
        multimask_output=False,
    )

Sam2Config

autodoc Sam2Config

Sam2HieraDetConfig

autodoc Sam2HieraDetConfig

Sam2VisionConfig

autodoc Sam2VisionConfig

Sam2MaskDecoderConfig

autodoc Sam2MaskDecoderConfig

Sam2PromptEncoderConfig

autodoc Sam2PromptEncoderConfig

Sam2Processor

autodoc Sam2Processor - call - post_process_masks

Sam2ImageProcessor

autodoc Sam2ImageProcessor - preprocess

Sam2HieraDetModel

autodoc Sam2HieraDetModel - forward

Sam2VisionModel

autodoc Sam2VisionModel - forward

Sam2Model

autodoc Sam2Model - forward - get_image_features