Optimization of matching coded aperture with detector based on compressed sensing spectral imaging technology
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摘要:编码孔径光谱成像仪在实际应用中存在着编码模板与探测器分辨率不匹配从而降低系统分辨率的问题。针对该问题进行了两种情况分析，并通过数学理论建模给出了相应的解决方案。对于编码模板分辨率高于探测器分辨率这一情况，提出引入邻域嵌入超分辨技术的方法，实现了基于压缩感知的超分辨光谱成像。对于编码模板分辨率低于探测器分辨率这一情况，提出区块阈值划分的编码孔径，将编码微元按照区块阈值重新划分并进行灰度分级，从而实现低分辨率编码模板的高分辨率编码孔径。利用梯度投影稀疏重构（GPSR）算法进行数据立方体重建，实验结果表明：运用基于超分辨理论的编码孔径快照光谱成像系统所测得的光谱图像更精准，内容更丰富；采用基于区块阈值划分的编码孔径的编码孔径快照光谱成像系统具有更高的空间分辨率和光谱分辨率。结果证实优化后的编码孔径快照光谱成像系统，其分辨率和成像质量大幅度提升，并实现了高分辨率元件的100%利用。Abstract:In practical applications, when the coding template of coded aperture spectral imagers does not match the resolution of their detector, the resolution of the system is lowered. For this problem, by using a mathematical model for the Coded Aperture Snapshot Spectral Imaging system (CASSI), its limiting factors such as a mismatch between its coding template and the detector's resolution are analyzed and the corresponding solutions are given. Considering that the resolution of the coding template is higher than the resolution of the detector, it is proposed that super-resolution technology is introduced to the CASSI system to achieve super-resolution spectral imaging through compressed sensing. For cases in which the resolution of the coding template is lower than the resolution of the detector, a grayscale coding aperture with threshold partitioning grading is proposed to achieve a high-resolution coding mode, which can ensure the resolution of the coded aperture spectral imager. The GPSR algorithm is used to reconstruct the data cube. Experimental results show that the spectral image measured by the CASSI system based on super-resolution theory is more accurate and richer in content. The CASSI system based on a coded aperture with grayscale grading is employed and shown to have higher spatial resolution and spectral resolution. It can be concluded that after optimization, the resolution and imaging quality of the CASSI system are greatly improved and its high resolution components are fully utilized.
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图 1编码孔径快照光谱成像系统的结构示意图
Figure 1.Structral diagram of coded aperture snapshot spectral imaging system
图 7一般的CASSI系统(上)与改进型(下)重建结果对比
Figure 7.Comparison results of general CASSI system(up) and improved reconstruction (down)
图 8目标场景和地物光谱仪在3个点处的特征曲线
Figure 8.Characteristic curves of target scene and ground-object spectrometer at three points
图 9一般CASSI系统、超分辨CASSI系统及商用光谱仪的光谱曲线对比
Figure 9.Comparison of spectral curves of a general CASSI system, a super-resolution CASSI system and a commercial spectrometer
图 10编码模板及其区块阈值划分处理后的示意图
Figure 10.Schematic diagram of coding template and its block threshold partitioning
图 11一般的CASSI系统(上)与改进型(下)重建结果对比
Figure 11.Comparison of reconstruction results of general CASSI system(up) and modified CASSI system(down)
图 12一般CASSI系统、区块阈值划分CASSI系统及ASD光谱仪的光谱曲线对比
Figure 12.Comparison of spectral curves of a general CASSI system, a block threshold partitioning CASSI system and ASD spectrometer
表 1系统参数
Table 1.System parameters
元件 参数 DMD: 分辨率：1 024×768 空间光调制器DLP1100 微元尺寸：13.68 μm×13.68 μm 探测器： 分辨率：656×492 GuppyPro F-032C 像元尺寸：7.4 μm×7.4 μm 分光原件 透射式光栅 光谱范围 450~680 nm 光谱分辨率 ≤20 nm@540 nm 系统焦距 75 mm 系统F 4 
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表 23种实验条件下的测量结果对比
Table 2.Comparison of measurement results under three experimental conditions
像素尺寸(μm) 分辨率(像素) Δc Δd 编码孔径 空间分辨率 光谱通道 一般CASSI 27.36 29.7 160×160 160×160 8 超分辨CASSI 13.68 29.7 320×320 320×320 8 区块阈值划分CASSI 13.68 9.9 320×320 480×480 24 下载:
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