**1. Introduction**

Globally, diabetes is among the top ten causes of death in adults and was estimated to have caused the 4.2 million deaths resulting from diabetes and its complications in 2019. India is ranked second with almost 77 million cases in the list of countries that are most affected with diabetes while China leads the list with over 116.4 million diabetics. An estimated 15.8% (20.4 million) of live births are affected by hyperglycemia in pregnancy in 2019. This represents 9.3% of the world's population in this age group. In the International Diabetes Federation (IDF) South-East Asia Region, 57% of adults aged 20–79 years with diabetes are undiagnosed. An estimated 1.1 million children and adolescents (aged under 20 years) have type 1 diabetes. The total number is projected to rise to 578 million (10.2%) by 2030 and to 700 million (10.9%) by 2045. Annual worldwide health spending on diabetes is estimated to be USD 760 billion. It is projected that expenditure will reach USD 825 billion by 2030 and USD 845 billion by 2045 [1].

Fifty percentage of patients with diabetes have some degree of neuropathy, resulting in at least one-foot ulcer throughout the lifetime in 15% of the cases. Neuropathic foot ulceration is a foremost cause of illness in patients with diabetes [2]. Diabetes patients have demonstrated that there are significantly increased skin temperatures and recognizable thermal radiation patterns, which differentiate them from healthy people. Thermometry of the diabetic foot is an impressive way to evaluate the risks associated with foot ulceration [3]. It has been revealed that monitoring foot skin temperature contributes to the clinical information before other medical signs of the wound can be recognized [4]. Differences in plantar thermal patterns in normal controls and non-ulcer diabetic patients were studied using thermometry [5]. Though, it has not been abundantly clarified to what extent the individual inconsistency of the plantar thermal patterns shows different trends between healthy and diabetes patients. Thermal imaging technology is capable to measure insignificant temperature irregularities to oversee some physiological circumstances [6]. Understanding of the temperature profile of foot is quite important to evolve thermal imaging system for detection of diabetic foot.

### **1.1 Temperature profile of foot**

A healthy foot having healthy blood flow through healthy blood vessels whereas the decreased blood flow in the diabetic foot cause damage to organs like the leg and foot. The lack of blood flow caused by diabetes decreases the body's ability to heal from injuries. The assessment of raised temperature distribution with infrared thermometry in the diabetic foot is employed to identify the varying metabolic activity. Skin examination with an IR thermometer is flexible to repetitive wound care practice and home health. Nevertheless, the IR thermometry method becomes difficult and insufficient when measuring the temperature at many points on the foot [7, 8]. The liquid crystal thermograph methodology provides the temperatures pattern of the foot area as a colored foot imprint on a plate encompassed by layers of compressed thermochromics liquid crystals. The imprint persists for few minutes and then gradually disappear away. A temperature profile cannot be obtained for non-contact areas like an arch [9, 10].

Employing high-resolution and very sensitive thermal imaging cameras, the heat radiation from the matter is acquired and processed into an image of the thermal map which can then be stored and analyzed on screen and computer. Increased temperature investigation can be attained even for non-contact foot areas. Thermal images of diabetic feet reveal that it is 2.2°C colder than the lower leg, and usually the toes are not observable to the camera as they have become so hypothermic. Diabetic foot can arise several years before repetitive blood glucose levels indicate diabetes, and as such, can provide the patient time to treat the illness before everlasting nerve impairment occurs to the foot [11–13].

Though thermal imaging system is a promising screening tool for diabetic foot, diagnosis is usually done manually by skilled professionals. Hence, analyses made from thermograms are greatly subjective in nature. In order to overcome issues such as lack of proficient personnel, an efficient machine learning framework needs to be developed. The developments made in thermography and pattern recognition techniques are used to develop a competent system for detection of diabetic foot in plantar thermograms. Such a system can be used for screening of diabetes mellitus patients in developing countries, specifically by primary health care specialists in rural areas where health care expert is lacking.
