Thermal Camera

Introduction

Thermal cameras, also known as infrared or thermographic cameras, are devices that detect and visualize the heat (infrared radiation) emitted by all objects with a temperature above absolute zero. Operating in the infrared spectrum (typically 8–14 µm), they convert thermal energy into electrical signals using a sensor array—usually a microbolometer—combined with a special lens (often made of germanium), a digital signal processor, and a display unit. These cameras use pseudo-color palettes to represent temperature differences, with warmer areas shown in bright colors and cooler areas in darker tones. The science behind thermal imaging relies on the principle that higher temperatures emit more infrared radiation, and surface emissivity (e.g., human skin ≈ 0.98) plays a key role in accurate detection. Originally developed for military applications, thermal cameras are now widely used in medical diagnostics, psychological and emotional research (e.g., biofeedback and stress monitoring), industrial inspection, building diagnostics, night surveillance, wildlife observation, and increasingly, in smartphone-compatible consumer tools. Recent advances have made thermal imaging more compact, accessible, and integrable with artificial intelligence, making it a powerful tool in health tech, emotion analysis, and real-time  physiological monitoring.

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Visible Light vs. Infrared light

Why do all objects emit IR radiations?

Every object you see—even things that look still like a table or a rock—has tiny particles (atoms and molecules) inside it that are always moving. These tiny particles that make up matter are always in motion, a phenomenon known as Brownian motion.

This motion happens as long as the object’s temperature is above absolute zero (−273.15°C).

When these tiny particles move, they create a type of energy called electromagnetic radiation. This energy travels in waves, just like light.

The kind of waves that get created depends on how hot the object is:

(i) Cooler objects (like a person or a wall) give off infrared waves, they are not hot enough to emit visible light.
(ii) Hotter objects (like fire or the Sun) can give off visible light or even ultraviolet rays along with IR radiations.

Example:

• A human body (around 37°C) emits infrared radiation.

• A candle flame emits both infrared and visible light.

• The Sun (about 5,500°C at the surface) emits visible light, infrared, and ultraviolet rays.

“The warmer the object, the more energetic the vibrations.” This is explained by. Stephen-Boltzmann Law  [ E ∝ T4 ].

• Infrared = Heat Waves: Infrared radiation is just invisible light that carries heat. You can’t see it with your eyes, but you can feel it. For example: If you put your hand near a warm mug, you can feel heat without touching it—that’s infrared radiation reaching your skin.

    A thermal camera sees this IR radiation and shows it as colors to tell which areas are warmer or cooler.

Research in Happiness Science

Thermal Imaging and Emotion Detection

Thermal imaging detects and analyzes human emotions by measuring the temperature distribution on the face and body. This technology leverages the physiological link between emotional states and changes in blood flow, which manifest as subtle variations in skin temperature.

How Thermal Camera Explains Emotions:

• Emotional states such as stress, joy, fear, or empathy trigger autonomic nervous system responses, altering blood flow in facial regions.

• These changes cause localized increases or decreases in skin temperature, especially noticeable at the nose, forehead, and cheeks.

• Thermal cameras capture these temperature patterns, producing images that can be analyzed to infer emotional states.

Key Findings and Applications:

• Emotion Recognition:
  Thermal imaging can distinguish between a range of emotions. For example, positive emotions like joy often increase facial temperature, while negative emotions such as fear or anger tend to decrease it, particularly in the nasal area.

For example, Spanish researchers (Moliné et al., 2018) have studied the "Pinocchio effect". They found that the change in temperature of the nose and forehead can allow us to detect when people lie about facts (Pinocchio effect markers) with high accuracy.

• Empathy and Emotional Valence:
  Feelings of love or empathy may increase facial temperature, indicating greater emotional involvement. (Salazar-López et al., 2015) "The mental and subjective skin: Emotion, empathy, feelings and thermography"

This paper investigated how emotions like love and empathy influence facial temperature, using infrared thermography in healthy adults. Participants were shown emotional stimuli while facial thermal responses were recorded. Love was associated with increased temperature in areas like the nose, mouth, and forehead, reflecting emotional arousal. Empathy tasks, such as watching others in pain, led to decreased nose temperature, especially in individuals with higher empathy scores. These findings highlight how bodily thermal responses correlate with emotional and empathetic experiences, independent of emotional valence.

• Accuracy and Multimodal Integration:
  Recent research demonstrates that thermal imaging alone can achieve high accuracy (up to 79% for cognitive stress and 78% for moral elevation) in emotion detection. Combining thermal imaging with other physiological measures, like remote photoplethysmography (r-PPG), further improves accuracy to over 85%. ( Liu I, Liu F, et al., 2024 )

Demonstration Video

Experiments of Thermal Camera

Experiment - 1: Thermal Imaging Analysis of Human Physiological Responses to Social Interaction

Aim

To examine facial temperature changes during escalating levels of social boundary - social distance, personal distance, and touch using thermal imaging.

Introduction

Human social interactions are rich with non-verbal cues that convey emotional and psychological states. Among these, eye contact, physical proximity, and touch play a significant role in shaping interpersonal communication. These cues can trigger measurable emotional and physiological responses, including changes in heart rate, skin conductance, and facial temperature. For instance, direct gaze or close physical presence often increases arousal or social awareness, while physical touch may elicit stronger affective reactions such as comfort, anxiety, or connection. In recent years, thermal imaging has emerged as a powerful, non-invasive method for monitoring such physiological responses. Thermal cameras detect subtle variations in skin temperature, which can be influenced by changes in blood flow regulated by the autonomic nervous system. These temperature shifts offer insight into internal states like stress, arousal, or emotional engagement without requiring physical sensors or subjective reporting.

Objective

The primary aim of this experiment is to document how facial skin temperature responds to three distinct social interaction conditions:

1. Social Distance – where a person is observed from a distance.

2. Personal Distance – where the observer moves closer.

3. Touch Interaction – where physical contact is initiated.

By capturing these interactions with a thermal camera, the experiment seeks to visualize and interpret the autonomic changes associated with increasing levels of social engagement.

More About Experiment

Experiment - 2: Visualization Interventions

Aim

To observe the thermal facial responses upon Happy and sad visualizations.

Introduction

Our emotions don’t just stay in our mind, they quietly show up on our bodies too. When we’re happy, sad, or stressed, our body reacts, sometimes in ways we don’t even notice. One fascinating way to observe these reactions is by using a thermal camera. It allows us to see small changes in skin temperature, especially on the face, without even touching the person.

Inspired by these findings, we decided to explore whether imagining a happy or sad memory would lead to similar changes in facial temperature. Since the face is rich with blood vessels and sensitive to emotion, even a slight emotional shift might be visible on a thermal image.

Expected Outcome

While visualizing a sad or emotional moment, participants would show a cooling effect on certain facial regions, especially around the nose-tip, as their stress levels increased.

More about Experimentation

References

• Salazar-López, E., Domínguez, E., Juárez-Ruiz de Mier, R., Martínez-Íñigo, D., Gómez-Milán, E., & Fernández-Santaella, M. C. (2015). The mental and subjective skin: Emotion, empathy, feelings and thermography. Consciousness and Cognition, 34, 149–162. https://doi.org/10.1016/j.concog.2015.04.003

• Moliné, M., Fernández-Caballero, A., González-Marrón, J., & Sánchez, M. C. (2018). Thermography and the Pinocchio Effect: Measuring lies with facial temperature. Thermohuman.  

https://thermohuman.com/2024/02/28/thermography-and-emotions

• Liu, I., Liu, F., et al. (2024). Multimodal analysis of emotion detection through thermal imaging and photoplethysmography. arXiv preprint. 

https://arxiv.org/pdf/2401.09145

• ScienceDirect. (n.d.). Infrared radiation. Physics and Astronomy Topics. https://www.sciencedirect.com/topics/physics-and-astronomy/infrared-radiation

• Thermohuman. (2024, February 28). Thermography and emotions. Thermohuman. https://thermohuman.com/2024/02/28/thermography-and-emotions

• PubMed Central (PMC). (n.d.). Article on thermography and emotion. https://pmc.ncbi.nlm.nih.gov/articles/PMC4286005/