## 1 Introduction  
Low-cost and miniaturized microscopes provide various functional roles in applications ranging from disease diagnostic [1; 2; 3], food monitoring [4; 5], and biological research [6; 7]. Portable microscopic imaging systems are also useful for point-of-care testing (POCT) or remote health care systems [8; 9]. Recently, low-cost, compact microscopes that are capable of not only COVID-19 screening but also live cell imaging have been introduced [6; 10]. However, miniaturized microscopes often have obstacles regarding imaging performance, such as low-image-contrast and low-spatial-resolution due to the limitations of optical power [11]. To address these limitations, a microscope with functional illuminations and image processing techniques has been introduced to acquire high-contrast and high-resolution images [12; 13]. Illuminations, such as LED arrays and smartphone displays, allow for the acquisition of various contrast images, and these images are improved with image reconstruction [14; 15]. Moreover, a laser diode is used in fluorescence imaging applications, which additionally require a filter to distinguish between emission light and noise [16]. The miniaturized microscope exhibits various imaging applications imaging such as Microscope [16; 17; 18], dark-field [19; 20], and phase-contrast imaging [21; 22]. The portable microscopic systems are mostly equipped with an additional lens and light-emitting diode (LED) illumination on a smartphone or a compact camera to implement functional magnified imaging. The smartphone-based microscopes have compact and portable, whereas the systems often lack a lift stage for fixing and focusing a sample. Such portable microscopes can be classified into a transmission type and a reflection type microscope according to image acquisition methods. Transmission-type optical microscopy can detect a microstructure through the light on the back of a sample [23; 24; 25], but this approach can only observe transparent samples such as sectioned biological specimens. Reflection optical microscopy can capture a microscopic image by using reflected light from a sample [11; 26]. However, the reflected light microscopy acquired low-contrast images when observing a transparent sample due to low reflection signals. Solid immersion lens (SIL) microscopy is a technique to increase spatial resolution by placing a high-refractive-index hemisphere or microsphere on a target object [27; 28]. The SIL technique offers a high numerical aperture (NA), high magnification, and high resolution by efficiently collecting light [29; 30]. However, the SIL requires highly precise alignment between the target and solid material, such as a microsphere, to observe desired locations. A precision stage is mainly used for positioning the solid material; thus, the whole system becomes bulky. Here we report a multi-mode compact microscope (MCM) for high-contrast and high-resolution imaging, as shown in Figure 1a,b. The MCM features ring-type lighting on the top surface, an imaging module, a compact lift stage, and bottom LED illumination. The image-capturing module consists of an objective lens and image sensor (Sony 8 MP IMX 219 sensor, pixel size: 1.12 \(\upmu\)m \(\times\) 1.12 \(\upmu\)m, 30 fps). As shown in Figure 1c, a compact microscope housing mounts all components, including a processor board (Raspberry Pi 4 Model B) for image processing and a customized circuit board for illumination control. The total cost to configure the MCM is about USD 300, and this cost is reasonable compared to other low-cost microscopes that require a smartphone. The focused image can be adjusted by positioning a sample location with the lift stage. The LED illumination controls allow assorted microscopic imaging, and high dynamic range (HDR) reconstruction offer high-contrast images. The processed images are transmitted to an external monitor. The resolution and magnification of the MCM were increased through a virtual magnified image of a microlens array (MLA).