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摘要:
针对Micro LED缺陷检测中可见光(RGB)与光致发光(Photoluminescence, PL)图像因模态差异较大而难以实现高精度配准的难题,本研究致力于开发一种具备亚像素级精度和高鲁棒性的多模态图像配准方法,从而建立芯片物理结构与电学性能之间的映射关系。我们提出了一种结合结构特征约束与双向残差优化的配准方法:首先,基于Micro LED规则阵列的几何特性,设计了差异化的特征检测策略:在RGB图像中,通过椭圆拟合和基于密度的空间聚类算法(Density-Based Spatial Clustering of Applications with Noise, DBSCAN)精确提取电极中心;而在PL图像中,则采用改进的分水岭算法结合亚像素精修技术来定位芯片中心。其次,在配准优化阶段构建了双向残差约束框架,并引入基于残差分布的置信度加权机制,通过迭代重加权最小二乘法求解最优仿射变换参数。实验结果表明,本方法的平均绝对误差(Mean Absolute Error, MAE)为0.823像素,达到了亚像素级精度;与基线方法相比,MAE显著降低了94.2%。同时,均方根误差(Root Mean Square Error, RMSE)为0.996像素,最大误差(Max Error)控制在2.839像素以内,内点率达到75.0%,单次配准平均耗时仅为0.036秒,与互信息(Mutual Information, MI)等传统方法相比,运行效率实现了数量级提升。基于上述策略,本方法有效克服了多模态图像中的特征失配和异常点干扰问题,在配准精度、鲁棒性和效率方面均优于传统方法,为Micro LED芯片的精确缺陷检测与多模态分析提供了可靠的技术基础。
Abstract:To address the challenge of achieving high-precision registration between visible light (RGB) and photoluminescence (PL) images in Micro LED defect inspection, which arises from substantial modality differences, this study introduces a robust multimodal image registration approach capable of attaining sub-pixel accuracy, aiming to establish a direct mapping between the physical structure and electrical characteristics of the chips. We propose a registration method that integrates structural feature constraints with bidirectional residual optimization. First, leveraging the geometric regularity of Micro LED arrays, a tailored feature detection strategy is employed: electrode centers in RGB images are accurately extracted via ellipse fitting and Density-Based Spatial Clustering of Applications with Noise (DBSCAN), while chip centers in PL images are localized using an enhanced watershed algorithm with sub-pixel refinement. Second, during the registration optimization stage, a bidirectional residual constraint framework is constructed, incorporating a confidence weighting mechanism derived from residual distribution analysis. The optimal affine transformation parameters are then estimated using an iterative reweighted least squares method. Experimental results demonstrate that the proposed method achieves sub-pixel-level accuracy, with a mean absolute error (MAE) of 0.823 pixels, representing a 94.2% reduction compared to baseline methods. The root mean square error (RMSE) is 0.996 pixels, the maximum error remains below 2.839 pixels, and the inlier rate attains 75.0%. Each registration process takes only 0.036 seconds on average, achieving an order-of-magnitude improvement in computational efficiency over traditional mutual information (MI) methods. By effectively mitigating feature mismatch and outlier interference in multimodal images, the proposed method outperforms conventional approaches in terms of registration accuracy, robustness, and efficiency, thereby providing a reliable technical foundation for precise defect detection and multimodal analysis of Micro LED chips.
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表 1 本文方法的配准结果
Table 1. Registration results of the proposed method
评价指标 数值 单位 几何精度 均方根误差(RMSE) 0.996 px 平均绝对误差(MAE) 0.823 px 最大误差(Max Error) 2.839 px 内点率(Inlier Rate) 75.0 % 图像质量 结构相似性(SSIM) 0.334 - 互信息(MI) 1.352 nats 运行效率 配准时间(Time) 0.036 s 表 2 四组Micro LED图像配准评价指标
Table 2. Registration evaluation metrics for four Micro LED image sets
组别
(Group)均方根误差
(RMSE)平均绝对误差
(MAE)最大误差
(Max Error)内点率
(Inlier Rate)结构相似性
(SSIM)互信息
(MI)时间
(Time)(1) 0.832 0.742 1.907 86.8% 0.346 1.287 0.034 (2) 0.963 0.777 3.130 74.4% 0.348 1.286 0.035 (3) 1.071 0.884 3.684 57.6% 0.328 1.287 0.032 (4) 1.611 1.316 3.806 63.6% 0.362 1.343 0.043 表 3 不同配准方法的实验结果
Table 3. Experimental results of different registration methods
组别
(Group)方法 均方根误差
(RMSE)平均绝对误差
(MAE)内点率
(Inlier Rate)结构相似性
(SSIM)互信息
(MI)时间
(Time)(1) ORB 1384.348 1288.305 - 0.002 0.009 8.150 WLD NaN NaN NaN 0.426 1.274 57.661 MI NaN NaN NaN 0.426 1.305 55.491 Phase Correlation NaN NaN NaN 0.515 0.065 3.853 本文方法 0.832 0.742 86.8% 0.346 1.287 0.034 (2) ORB 2.040 1.344 0.9% 0.705 0.295 8.151 WLD NaN NaN NaN 0.431 0.668 95.604 MI NaN NaN NaN 0.418 1.192 36.039 Phase Correlation NaN NaN NaN 0.470 0.367 3.915 本文方法 0.963 0.777 74.4% 0.348 1.286 0.035 (3) ORB 2.240 1.381 0.8% 0.376 0.150 7.995 WLD NaN NaN NaN 0.417 1.145 35.734 MI NaN NaN NaN 0.436 1.226 39.203 Phase Correlation NaN NaN NaN 0.511 0.040 3.844 本文方法 1.071 0.884 57.6% 0.328 1.287 0.032 (4) ORB 1207.783 1098.011 - 0.002 0.015 8.257 WLD NaN NaN NaN 0.440 1.107 96.789 MI NaN NaN NaN 0.464 1.239 45.807 Phase Correlation NaN NaN NaN 0.535 0.006 3.932 本文方法 1.611 1.316 63.6% 0.362 1.343 0.043 注:表中“-”表示配准失败,无法计算内点率;“NaN”表示对应方法的配准机制不依赖特征点匹配,基于点对的几何精度指标(RMSE, MAE, 内点率)不适用。该类方法的性能通过图像质量指标(SSIM、MI)和配准时间进行评估。 表 4 消融实验结果
Table 4. Ablation study results
组别
(Group)均方根误差
(RMSE)平均绝对误差
(MAE)最大误差
(Max Error)时间
(Time)G0 39.538 14.311 172.762 0.004 G1 3.147 2.491 8.573 0.004 G2 1.690 1.394 4.614 0.008 G3 1.424 1.133 4.093 0.029 G4(Ours) 0.996 0.823 2.839 0.036 -
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