## 1 Introduction  
V Vitamin C (VC) is an essential micronutrient and appears as a colorless crystal that is soluble in water. VC is necessary for preventing scurvy and is often called ascorbic acid in medicine. VC plays an important role in the synthesis of neurotransmitters, steroid hormones, carnitine, the conversion of cholesterol to bile acids, tyrosine degradation, and metal ion metabolisms. The role of ascorbic acid as a biological reducing agent may be linked to its prevention of degenerative diseases, such as cancer and cardiovascular diseases. Thus, VC is of great importance to one's overall health. Most plants and animals synthesize ascorbic acid for their own requirements. However, humans cannot synthesize ascorbic acid due to a lack of the enzyme gulonolactone oxidase. Hence, ascorbic acid must be supplemented, mainly through fruits, vegetables, and tablets [1]. Therefore, an accurate measurement of VC in foods is important to determine VC intake and has a significant influence on dietary health.  
There are many methods for the determination of VC, such as high-performance liquid chromatography (HPLC) [2; 3; 4; 5], fluorescence spectroscopy [6], spectrophotometry [7], and electrochemical analysis [8; 9; 10; 11]. In recent years, new methods have been proposed, including resonance Rayleigh scattering (RRS) [12] and flow injection photosensitized chemiluminescence [13]. However, these methods require expensive instruments, such as electron microscopes and photomultiplier tubes, or have complicated chemical reaction processes.  
Spectrophotometry is used to determine VC based on the color reaction. By measuring the absorbance or luminescence intensity of light at a specific wavelength, the concentration of the product is obtained. It is often used for VC determination with a high sensitivity for 0-8 \(\upmu\)g/mL, and was applied here to compare with our proposed method [7].  
The development of computer image processing and imaging technology has made cameras widely used in various fields. In soil analysis, the RGB (red-green-blue) values of digital images and the derived soil indices were used to determine iron oxides and fines in soil [14]. A digital camera was also used for determining the iron and residual chlorine in water using N,N-diethylphenylenediamine [15]. In addition, image acquisition was carried out using a digital camera and image processing technology was used to acquire image information to determine the water turbidity, nitrite, ammonia nitrogen, sulfide, and phosphate contents, etc. [16; 17]. The detection method that combines a digital camera and image processing technology has the advantages of simple design, convenient operation, and visualization, which verifies the feasibility of using a digital camera in trace analysis.  
The turbidimetric method is often used for medical and biological detection [18; 19]. The principle is that suspended particles absorb and scatter the incident light, and the intensity of scattering and absorption is positively proportional to the concentration of suspended particles. The concentration of the detected substances in the solution can be deduced by measuring the intensity of transmitted light. However, there is no turbidimetric method on the basis of iodine suspensions using a camera.  
Most of the existing VC measuring methods require specialized instruments, or complicated operations, and cannot easily measure VC. There is a need for a VC measuring method that is easy to operate and does not require expensive instruments. The goal of the present work was to measure VC content using a typical infrared camera. In this work, an infrared camera was used to capture images of light penetrating through iodine suspensions that were prepared by the reaction between the aqueous VC solution and iodine ethanol solution. The VC concentration was obtained from the attenuation of incident light, which was indicated by the color component and gray information of the image.