## 3 Multi-Illumination for High-Contrast Imaging  
Various targets were captured in different lighting environments for multi-illumination imaging, as shown in Figure 4a. Figure 4b,c show stratified squamous epithelium and cardiac muscle cells from mice captured in the transmission light mode. The transmission optical microscopy mode using the top illumination can be used for biomedical research and disease diagnosis because this mode is effective for observing transparent specimens. Figure 4d exhibits gold wires bonded on an image sensor chip, and Figure 4e shows an SMD capacitor mounted on a printed circuit board (PCB). The reflection light microscopy mode can efficiently observe the defects of soldering interconnection on circuit boards in resource-limited areas. A dual illumination mode that simultaneously implements the bottom and top illuminations was compared with a bottom single illumination mode. The experimental results show that the single illumination modes offer low-contrast images that are difficult-to-distinguish leaf hairs, as shown in Figure 4f,g. On the other hand, the dual illumination mode clearly observes leaf hairs due to the additional reflection lights of the top illumination with a different color, as shown in Figure 4h. These results indicate that the dual illumination mode provides high-contrast imaging in complex 3D structures. Figure 4: Multi-mode illumination imaging of MCM. (**a**) Schematic illustrations of multi-mode illumination imaging. The transmission light microscopy mode uses the bottom illumination, and simultaneously  
Figure 3: Imaging performances of MCM. (**a**) Measured MTF curves according to illumination directions and targets through the slanted-edge method. (**b**) Thru-focus MTF according to target distances. The MTF was determined at the spatial frequency of 50 line pairs per mm. utilizes the bottom and top illuminations. The captured microscopic images of (**b**) stratified squamous epithelium and (**c**) cardiac muscle in the transmission light mode. The reflected microscopic images of (**d**) gold wires on an image sensor and (**e**) a silicon capacitor packaged on a circuit board. The captured images of leaf in (**f**) the transmission light mode and (**g**) the reflection mode. (**h**) Dual illumination imaging of leaf, which offers a high-contrast leaf hair image. The scale bars are 100 \(\upmu\)m.  
Dark-field microscopy was demonstrated by using the MCM with a dark-field stop on the bottom illumination, as shown in Figure 5a. The central light that directly illuminates a sample is blocked by a dark-field stop, and the outer light is reflected by the slide and transmitted to the sample. The reflected light is scattered on the sample, and the objective lens collects the scattered light. Figure 5b,c show the dark-field microscopic images of yeast and sugar captured through the dark-field compact microscope. The background appears black because scattered light only is exhibited in the sample, excluding the background. The dark-field microscopic images offer higher contrast compared to the bright-field images by reducing background noise, as shown in Figure 5d,e. High dynamic range (HDR) imaging was performed by using various contrast images acquired by different exposure times, as shown in Figure 6a [34]. The reconstruction of image arrays assists in increasing the image contrast [35; 36; 37]. For the HDR reconstruction, the captured images were aligned by matching the edge of the images. The aligned images were merged by computing a weighted average of each pixel. The weight of intensity was decided by the contrast, saturation, and well-exposedness of images. The HDR image algorithm comprises the signal representation of a Laplacian decomposition and Gaussian pyramid. As shown in Figure 6b, six images with different contrasts were captured by increasing the exposure times from 0.1 ms to 1.1 ms. Then, the captured images were integrated into a single HDR image through the HDR image processing algorithm shown in Figure 6c.