## 1 Introduction  
The microscopic pore structure of a reservoir refers to the geometry, size, distribution, and mutual connectivity of the pores and throats in the reservoir rock [1; 2], which directly affects the development of the reservoir pore space. The pore space of tight sandstone reservoirs is divided into three levels: millimeter pore, micron-scale pore, and nano-scale pore. [PERSON] et al. discovered nano-scale pores for the first time in a study of unconventional reservoirs in China by applying field emission scanning electron microscopy and X- CT (X-ray computed tomography) reconstruction techniques [3]. From the millimeter pore to the nano-scale pore, many analytical methods, including experiments and numerical simulations, have been applied to the pore structure and characterization of tight sandstone. Different methods are suitable for different samples (Table 1). Nuclear magnetic resonance logging techniques [4; 5; 6], fluid injection experiments [7; 8; 6], and image observation method are the three major categories [9; 10; 11]. Nuclear magnetic resonance logging technology based on rock resistivity parameters is mainly used to determine the reservoir pore size distribution. The fluid injection experiment represented by the mercury intrusion method can indirectly obtain the parameters of pore characteristics such as reservoir space distribution and pore size through the mercury intrusion curve, but it cannot directly observe the characteristics of reservoir space and pore throat, compared with the scanning electron microscope and nano-CT technology. Scanning electron microscopy and X-ray CT were used as experimental guides [12; 13]. The results of the study were mostly based on the quantitative analysis of the geometry and connectivity of pore throats. There are still deficiencies in studying micron pore size distribution. For the quantitative analysis of tight sandstones, gas adsorption, high-pressure mercury injection, and helium gas porosity are the main methods. High-pressure mercury injection is suitable for the analysis of nano-pore throats [14]. Helium porosity can reflect the pore size distribution of the entire reservoir, but it cannot measure some nano-scale pores [15; 16]. In addition, many scholars have combined these experiments with numerical simulation to quantitatively analyze the pore throat characterization. In this paper, casting thin sections, scanning electron microscope, and high-pressure mercury injection experiments were taken as the experimental methods, and Matlab software was used as the processing method to quantitatively analyze the pore throat characteristics of tight sandstone in the study area from the two dimensions of nano-scale pore and micro-scale pore throat.  
The Matlab software has a powerful ability to process image and data, and has been applied by scholars in various research studies, including biology, materials science, and mechanical engineering [17; 18; 19; 20; 21; 22]. Many scholars use Matlab to study the pores of various types of rocks and materials as well. This article takes the tight sandstone of the He8 section of the Ordos Basin as the research sample, using the Matlab built-in application 'Color Threshold' and related functions to quantify the pore-related characteristics and parameters of the samples.