Non-Uniformity Correction
lastmod 2025-03-13created 2025-03-136 edits
In thermal cameras, NUC (Non-Uniformity Correction) is the process of correcting non-uniform thermal images caused by sensor temperature changes or sensitivity differences between pixels.
About
Have you ever been startled when the thermal image suddenly froze and the camera made a "click" sound? There is no need to worry, because the camera is performing non-uniformity correction. Why is non-uniformity correction necessary?
Non-uniformity correction (NUC) is performed to adjust for small detector drift that occurs as the scene and environment being measured change, and it sometimes happens when the camera's own heat interferes with temperature measurement. To keep measurement accuracy high, the camera measures the infrared radiation emitted by its built-in optics and then adjusts the image according to that reading. NUC adjusts the gain and offset of each pixel to produce a more accurate, higher-quality image.
During NUC, the camera shutter has to block the path between the lens and the detector, so you hear a "click" and the image stream pauses temporarily. The shutter serves as a flat reference surface so the detector can calibrate itself and return to a thermally stable state.
This feature is commonly used in uncooled infrared cameras, but some cooled infrared camera models use it as well. The technical term is Korean: 플랫 필드 보정 (FFC, flat field correction).
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| Performing non-uniformity correction properly improves image quality. |
When does the camera perform NUC?
NUC is usually performed when the device is first turned on. Once the camera has warmed up and reached a stable operating temperature, the NUC interval becomes longer. Thermal measurement is possible after waiting only about 20 seconds after powering on the camera, but to improve temperature measurement accuracy, a warm-up time of at least 20 minutes in a stable environment is recommended.
The camera performs NUC automatically, but you can also trigger NUC manually before measuring an important temperature or capturing an important image. Performing NUC manually gives the most accurate results.
Can the user control NUC so it runs only when wanted?
As mentioned above, NUC plays a significant role in improving temperature readings. Without NUC, temperature readings risk becoming unstable. Most handheld cameras do not allow NUC to be disabled, but some automation and scientific devices have a feature that switches NUC from automatic to manual mode. In that case, you can precisely control when the camera performs NUC using software or hardware signals.
How to set manual mode on Teledyne FLIR: How do I manually control the NUC (auto-calibration) in the A35/A65? | Teledyne FLIR
ChatGPT answer
🔥 What is NUC (Non-Uniformity Correction)?
A thermal camera detects infrared radiation and represents temperature visually, but the physical characteristics of the sensor itself can cause the following problems.
- Sensitivity differences between pixels: every pixel of a thermal sensor should detect heat in the same way, but tiny differences arise in the manufacturing process, so certain pixels may appear brighter or darker.
- Sensor temperature changes: during long use or when the ambient temperature changes, the sensor temperature changes and output values may shift.
- Ghost images (afterimages): traces of the image from previous frames may remain, producing distorted results.
NUC (non-uniformity correction) is needed to solve these problems.
🛠️ How NUC works
NUC usually works in the following ways.
- Shutter-based (Shutter-Based NUC)
- Some thermal cameras have a built-in shutter (Shutter) or flat field calibration (FFC, Flat Field Correction) feature.
- At regular intervals, the shutter closes (covering the lens) and the sensor's own noise is analyzed to set a uniform reference value.
- A black screen may be shown while the shutter is closed.
- Shutterless (Shutterless NUC)
- Some high-end thermal cameras correct non-uniformity in real time using software algorithms, without a moving shutter.
- Pros - continuous capture is possible without shutter operation.
- Cons - quality may vary depending on the accuracy of the algorithm.
- Manual user correction (Manual NUC)
- When NUC does not run automatically in a certain environment, or the user needs to correct it directly, pressing the NUC button forces a correction.
⚠️ What happens when NUC runs
- When NUC runs, the screen may freeze momentarily or show a black screen briefly.
- Because it must be performed periodically, the screen may appear to freeze suddenly during use.
✅ How to adjust NUC
- Automatic NUC setting: some cameras can be set to perform automatic correction periodically.
- Manual NUC: correction can be forced by pressing a specific button.
- Use shutterless mode: to keep video uninterrupted, use a model that supports shutterless NUC.
🎯 Why NUC matters
- Improves the accuracy of thermal cameras and removes unnecessary distortion caused by sensor noise.
- An essential feature in fields where accuracy matters, such as industrial inspection, medical diagnosis, and security surveillance.
📌 Summary
- NUC (non-uniformity correction) is a feature that removes noise caused by pixel sensitivity differences and sensor temperature changes in thermal cameras.
- There are two types, shutter-based vs. shutterless, and it can be adjusted automatically/manually.
- The screen may freeze or flicker momentarily, but this is a normal process.
💡 If NUC runs too often or is inconvenient, you can also adjust the automatic NUC interval in the settings!