Object pose estimation plays a key role in many real-world applications, such as embodied intelligence, dexterous robot manipulation, and augmented reality.
In this field, the first task to receive attention is Instance-level 6D pose estimation, which requires annotated data about the target object for model training. Make the depth model object-specific and cannot be transferred to new objects. Later, the research focus gradually turned to category-level 6D pose estimation, which is used to process unseen objects, but requires that the object belongs to a known category of interest.
And Zero-sample 6D pose estimation is a more generalized task setting. Given a CAD model of any object, it aims to detect in the scene the target object and estimate its 6D pose. Despite its significance, this zero-shot task setting faces significant challenges in both object detection and pose estimation.
Figure 1. Zero-sample 6D object pose estimation task
Recently, segment all models SAM [1] has attracted much attention, and its excellent zero-sample segmentation ability is eye-catching. SAM achieves high-precision segmentation through various cues, such as pixels, bounding boxes, text and masks, etc., which also provides reliable support for the zero-sample 6D object pose estimation task, demonstrating its promising potential.
Therefore, researchers from Cross-Dimensional Intelligence, the Chinese University of Hong Kong (Shenzhen), and South China University of Technology jointly proposed an innovative zero-sample 6D object pose estimation framework SAM-6D. This research has been included in CVPR 2024.
SAM-6D achieves zero-sample 6D object pose estimation through two steps, including instance segmentation and Pose estimation. Accordingly, given an arbitrary target object, SAM-6D utilizes two dedicated sub-networks, namely Instance Segmentation Model (ISM) and Pose Estimation Model (PEM), to achieve the target from RGB-D scene images ; Among them, ISM uses SAM as an excellent starting point, combined with carefully designed object matching scores to achieve instance segmentation of arbitrary objects, and PEM solves the object pose problem through a local-to-local two-stage point set matching process. An overview of the SAM-6D is shown in Figure 2.
Figure 2. SAM-6D Overview
In general, SAM-6D technology The contributions can be summarized as follows:
SAM-6D uses the Instance Segmentation Model (ISM) to detect and segment arbitrary objects mask.
Given a cluttered scene represented by RGB images, ISM leverages the zero-shot transfer capability of the Segmentation Everything Model (SAM) to generate all possible candidates. For each candidate object, ISM calculates an object match score to estimate how well it matches the target object in terms of semantics, appearance, and geometry. Finally, by simply setting a matching threshold, instances matching the target object can be identified.
The object matching score is calculated by the weighted sum of the three matching items:
Semantic matching items - For the target object, ISM renders object templates from multiple perspectives, and uses the DINOv2 [3] pre-trained ViT model to extract candidate objects and object templates Semantic features and calculate correlation scores between them. The semantic matching score is obtained by averaging the top K highest scores, and the object template corresponding to the highest correlation score is regarded as the best matching template.
Appearance matching item ——For the best matching template, use the ViT model to extract image block features and calculate the correlation between it and the block features of the candidate object , thereby obtaining an appearance match score, which is used to distinguish objects that are semantically similar but have different appearances.
Geometric Match - Taking into account factors such as the shape and size differences of different objects, ISM also designed a geometric match score. The average of the rotation corresponding to the best matching template and the point cloud of the candidate object can give a rough object pose, and the bounding box can be obtained by rigidly transforming and projecting the object CAD model using this pose. Calculating the intersection-over-union (IoU) ratio between the bounding box and the candidate bounding box can obtain the geometric matching score.
For each candidate object that matches the target object, SAM-6D utilizes the Pose Estimation Model (PEM) ) to predict its 6D pose relative to the object CAD model.
Denote the segmented candidate object and the sampling point set of the object CAD model as 
and 
respectively, where N_m and N_o represent the number of their points; at the same time, the features of these two point sets are represented as 
and 
, and C represents the number of channels of the feature. The goal of PEM is to obtain an assignment matrix that represents the local-to-local correspondence from P_m to P_o; due to occlusion, P_o only partially matches P_m, and due to segmentation inaccuracy and sensor noise, P_m only partially matches Partial AND matches P_o.
In order to solve the problem of allocating non-overlapping points between two point sets, ISM is equipped with Background Token for them respectively, recorded as 
and 
, Then local-to-local correspondence can be effectively established based on feature similarity. Specifically, the attention matrix can first be calculated as follows:
Then the distribution matrix can be obtained
and 
represent softmax operations along rows and columns respectively, and 
represents a constant. 
The value of each row in (except the first row) represents the matching probability of each point P_m in the point set P_m with the background and the midpoint of P_o. By locating the index of the maximum score, you can find Points matching P_m (including background).
Once the calculation is obtained, all matching point pairs {(P_m,P_o)} and their matching scores can be gathered, and finally calculated using weighted SVD Object posture. 
Figure 3. Schematic diagram of the Pose Estimation Model (PEM) in SAM-6D
Using the above strategy based on Background Token, two point set matching stages are designed in PEM. The model structure is shown in Figure 3, which includes feature extraction, rough point set matching and fine point set Matches three modules.
The rough point set matching module implements sparse correspondence to calculate the initial object pose, and then uses this pose to transform the point set of the candidate object to achieve position encoding learning.
The fine point set matching module combines the position encoding of the sampling point sets of the candidate object and the target object, thereby injecting the rough correspondence relationship in the first stage, and further establishing dense correspondence relationships to obtain better Precise object pose. In order to effectively learn dense interactions at this stage, PEM introduces a novel sparse to dense point set transformer, which implements interactions on sparse versions of dense features, and utilizes Linear Transformer [5] to transform the enhanced sparse features into Diffusion back into dense features.
For the two sub-models of SAM-6D, the instance segmentation model (ISM) is built based on SAM and does not require The network is retrained and finetune, while the pose estimation model (PEM) is trained using the large-scale ShapeNet-Objects and Google-Scanned-Objects synthetic datasets provided by MegaPose [4].
To verify its zero-sample capability, SAM-6D was tested on seven core data sets of BOP [2], including LM-O, T-LESS, TUD- L, IC-BIN, ITODD, HB and YCB-V. Tables 1 and 2 show the comparison of instance segmentation and pose estimation results of different methods on these seven datasets, respectively. Compared with other methods, SAM-6D performs very well on both methods, fully demonstrating its strong generalization ability.
Table 1. Comparison of instance segmentation results of different methods on the BOP seven core data sets
Table 2. Comparison of attitude estimation results of different methods on BOP seven core data sets
Figure 4 shows the performance of SAM-6D on BOP seven Visualization results of detection segmentation and 6D pose estimation on three data sets, where (a) and (b) are the test RGB image and depth map respectively, (c) is the given target object, and (d) and (e ) are the visualization results of detection segmentation and 6D pose respectively.
Figure 4. Visualization results of SAM-6D on the seven core data sets of BOP.
For more implementation details of SAM-6D, please read the original paper.
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