Introduction

CMOS image sensors have revolutionized low-light imaging, offering significant advantages over traditional CCD sensors. This post explores how these advancements benefit outdoor applications such as long-range observation, surveillance, and global security.

Key Parameters for Low-Light Performance

Several parameters define a sensor’s effectiveness in dim conditions:

  • QE (Quantum Efficiency): Measures the sensor’s ability to convert incoming photons into electrons.
  • Read Noise: Lower noise levels improve image clarity.
  • Dark Current: Minimizes unwanted signals from thermal effects.
  • Uniformity: Ensures consistent performance across the sensor array.
  • MTF (Modulation Transfer Function): Evaluates how well the sensor preserves detail, especially in Near-Infrared (NIR) wavelengths.

CMOS sensors now outperform CCDs in all these areas. For instance, many security systems have successfully replaced daylight and low-light cameras with a single CMOS color uncooled camera.

Blooming and Smear: More Than Just Visual Artifacts

One area where CMOS has always held an advantage is handling blooming and smear:

  • Blooming: Caused by excessive light hitting adjacent pixels.
  • Smear: A vertical stripe artifact from bright spots, but it can also reduce dynamic range.

Understanding Dynamic Range Dynamic range—the ratio between the maximum output signal level and noise floor—is critical for outdoor scenes. Not only does a low noise floor ensure better sensitivity in dim conditions, but controlling smear is equally vital for capturing details during daylight imaging!

The Adimec Test Setup

To demonstrate how smear affects performance differently in CCD versus CMOS sensors, we conducted tests using:

  • A HDTV CCD camera.
  • A CMOS camera.

USAFA Target Images We captured images of a USAF target under two conditions:

  1. Short sensor integration time (bright daylight).
  2. Strong overexposure from reflective sources like sun or lasers.

The results showed that smear most impacts image quality when:

  • Integration times are short.
  • Parts of the image experience extreme brightness.

Detailed Analysis

By stretching video signals, we revealed differences in noise and pattern clarity:

CCD vs. CMOS Comparison

  • CCD: The background lacked uniformity, making fine patterns like text (e.g., “THORLABS”) difficult to read.
  • CMOS: While smear still affected the image, it performed better overall due to superior sensor technology.

Impact of Smear

Smear doesn’t just degrade aesthetics—it directly affects performance:

  1. Reduces contrast and makes details harder to spot.
  2. Increases noise in dark areas.
  3. Limits detection, recognition, and identification (DRI).
  4. Can cause white balance shifts in color images.

This explains why CMOS sensors with advanced technology outperform CCDs in challenging conditions like those tested by Adimec’s TMX series cameras.

Conclusion

Smear is a critical factor that can significantly impact image quality. While both sensor types are affected, modern CMOS sensors offer superior performance and reliability for demanding applications. As low-light imaging continues to evolve, staying informed about these technological advancements will help you choose the right tools for your projects.

Related Content:

  • CCD versus CMOS Update 2015
  • Comparison of CMOS IMX174 Cameras

Last Updated: 2025-09-04 20:47:47