Region-Aware Multi-View Inspection Using Deep Learning and Domain-Informed Decision Fusion

Srivishnu Ethirajulu Krishnaraj; Rishikesh R. Chopade

cs.CVOct 21, 2026

Region-Aware Multi-View Inspection Using Deep Learning and Domain-Informed Decision Fusion

Authors: Srivishnu Ethirajulu Krishnaraj, Rishikesh R. Chopade

Organizations: Bosch Limited, India

Abstract

Automated optical inspection of precision components with tiny surface defects remains challenging when different regions of the same component exhibit different defect characteristics and, therefore, different acceptance criteria. This paper presents a region-aware, dual-model inspection framework that combines instance segmentation of localized seat-region defects with image-level classification of global shaft-region anomalies. Rather than treating these two model detections as sufficient evidence for component rejection, a deterministic decision fusion layer that formalizes industrial Standard Operating Procedures is applied to the model outputs to make the final component level decision. A PLC-synchronized imaging system acquires 18 seat and 18 shaft images over a full 360-degree rotation to provide multi-view circumferential coverage. The framework was evaluated on 380 automotive fuel injector needles, covering representative operational defect types, using identical model predictions in all configurations. Direct model-output aggregation via simple union logic (where any single-view detection flags a rejection) identified all 104 non-conforming components but produced a component level false rejection rate of 57.6%. Inclusion of a complete decision layer maintained the observed non-conforming (NOK) recall of 100% while reducing the false rejection rate to 10.9%, corresponding to an 81.1% reduction in false-positive component decisions. The results demonstrate that formalized manufacturing acceptance criteria can complement sensitive visual models by translating frame-level detections into practical and traceable component-level decisions.

Figures & tables

Panel of Figure 1 — Fig. 1: Overall system architecture of the proposed PLC-synchronized, region-aware dual-model inspection pipeline (two camera views).

Fig. 2: Region-wise decomposition of the inspected component, including the upper one-third tip region, lower two-thirds seat region, and critical-line/edge region.

Parameter	Configuration
Views per rotation	18 views at 20 ∘ angular intervals
Seat camera	Basler ace U acA1300-200uc with Computar MLM-3XMP Lens
Shaft camera	Basler ace U acA1300-200uc with Fujifilm Fujinon HF35HA-1B lens
Lighting	$420\times 20$ mm LED bar light
Rotary fixture	Servo-driven
Seat-region resolution	$1280\times 1024$ pixels

TABLE I: Multi-view acquisition and inspection system configuration.

Fig. 3: Camera alignment and close-up view of the rotating component during inspection.

Category	Number of Images
Delamination	1,099
Grinding Marks	172
Droplet	671
Tip Damage	222
Grinding at Neck	27
Grinding Not Done	74

TABLE II: Class-wise image distribution of the seat-region dataset.

Subset	Number of Images	Approximate Percentage
Training	2,099	80%
Validation	261	10%
Test	261	10%
Total	2,621	100%

TABLE III: Partition of the seat-region dataset.

Parameter	Configuration
Architecture	Mask R-CNN ResNet-50-FPN V2
Framework	PyTorch and Torchvision
Initialization	COCO-pretrained Mask R-CNN V2 weights
Evaluated defect categories	Eight defect categories
Explicit preprocessing	None
Data augmentation	None

TABLE IV: Model and training configuration for Model I.

Class	Images	Approximate Percentage
Rotation OK	7,479	94.3%
Rotation Bad	454	5.7%
Total	7,933	100%

TABLE V: Class distribution of the shaft-region dataset.

Subset	Rotation OK	Rotation Bad	Total
Training	5,983	363	6,346
Validation	747	45	792
Test	749	46	795
Total	7,479	454	7,933

TABLE VI: Partition of the shaft-region dataset.

Parameter	Configuration
Model	EfficientNetV2-S
Framework	PyTorch and Torchvision
Initialization	ImageNet-pretrained weights
Input resolution	$224\times 224$ pixels
Input preprocessing	RGB conversion, resizing, and ImageNet normalization
Training augmentation	Brightness and contrast adjustment using ColorJitter

TABLE VII: Model and training configuration for Model II.

Fig. 4: Examples of seat- and shaft-region model outputs.

Component Status	Number of Components
Conforming/OK	276
Non-conforming/NOK	104
Total	380

TABLE VIII: Component-level distribution of the evaluation dataset.

Model	Metric	Result
Model I	Instance-level F1-score	43.79%
Model I	Instance-level recall	37.19%
Model I	Mean bounding-box IoU a	0.7069
Model II	Image-level accuracy	99.62%
Model II	Macro F1-score	98.32%
Model II	Rotation Bad recall	100% $(46/46)$

TABLE IX: Held-out test performance of the two inspection models.

Metric	MO	G-I	G-II	G-III	CDL
TP	104	104	104	104	104
FN	0	0	0	0	0
FP	159	120	40	114	30
TN	117	156	236	162	246
NOK recall (%)	100.0	100.0	100.0	100.0	100.0
FRR (%)	57.6	43.5	14.5	41.3	10.9

TABLE X: Component-level functional rule-group ablation results.

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Abstract

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