2023-07-06

2023-07-06

Done Today

• Learn how to process thermal images
• Check some relevant softwares

Thermal Camera

General answer for thermal images from any camera - you can't just convert grayscale level (or color if you already applied pallete to your image) to temperature values. You need to know some coefficients which relates to IR matrix. Some software may embed that data to image file metadata but there is no standard for that. Also, if you resaved your image file without knowing it, you'll probably lose that metadata.

Also, like plain visible-light camera, IR-camera can adapt it's range to current image. So, if you're shooting a human in a room, minimum temperature in your picture will be like 22°С (cold wall or floor), maximum will be like 37°C (hottest part of human body). In that case you'll get 256 gray levels covering range of 15 degrees, so black color is 22°С, white is 37°С (keep in mind proportion is not linear!). You move your camera to a cup of hot tea with like 60°С and your relation of gray level to temperature changes. So, you need to get coefficients for every frame.

It is possible to "fix" temperature range on some cameras but that depends on specific models.

More than that - most cheap thermal cameras don't deal with temperature values at all.

• (18) Tutorial m2ea - Usando DJI Thermal SDK para extraer temperaturas - YouTube
• Segmentation of thermal image based on temperature values - Python Help - Discussions on Python.org
• Nervengift/read_thermal.py: A small tool/lib to read temperatures and original photos from FLIR® thermal camera images.
• Thermal Vision: Measuring Your First Temperature from an Image with Python and OpenCV - PyImageSearch
• matlab - Normalization of Thermal image with range 0 to 40 - Stack Overflow

You can try to do that. It’s a less precise and more roundabout way of doing it. Simply compare your pixel to each of the pixels along the color bar, and find the closest match (Euclidean distance). That gives you a location along the colorbar that you can directly convert to a value.

• High Resolution Thermal Camera with Raspberry Pi and MLX90640 — Maker Portal
• DIY Thermal Camera with Raspberry Pi & AMG8833 Sensor
• Implementation of Thermal Camera for Non-Contact Physiological Measurement: A Systematic Review - PMC
• Thermal Imaging | Hackaday