One of the major challenges in surveillance and monitoring systems is inadequate availability of light. In the past, images captured in low lighting conditions were not clearly visible, had detail loss, and contained noise. Today, continuous improvements in sensor technology have given birth to a new generation of cameras that perform exceptionally well in low lighting conditions. This article intends to dive deep into the four factors that determine the low light performance of a camera.
What is low light performance, and the factors affecting it?
Low light performance is the ability of a camera to provide intelligible images even in low light conditions by preserving details and minimizing noise in the output image. Low light camera gives high-quality images even in extremely low lighting conditions as shown in the image below.
The factors that contribute to the low light performance of a camera are:
- Pixel Size
- Signal to Noise Ratio (SNR)
- Lens aperture
- Sensitivity
Let us now look at each of the above factors in detail.
Pixel Size
Pixel size is the physical dimension of a single pixel in an image sensor. Pixels are square wells that collect photons, and pixel size refers to the dimension of this square well. Pixel size in sensors that come with low light performance is typically 3µm or larger. The bigger the well, higher the number of photons collected, and hence better would be the performance of the camera in a low light environment.. This makes pixel size one of the most critical factors considered while choosing a camera for low light applications. However, it is to be noted that with increased pixel size, only fewer pixels can be accommodated in a compact imaging sensor causing either a reduction in resolution or an increase in the sensor size.
Signal to Noise ratio (SNR)
SNR or Signal to Noise Ratio, in simple terms refers to the ratio of the quantity of signal (valid image data) to the noise (invalid image data) in an image. A higher SNR indicates lesser noise. In an imaging sensor, dark current and transistor noise are some of the major noise components. A low-light camera comes with the ability to minimize these noise components to achieve a higher SNR thereby producing good quality images.
Lens aperture
Lens aperture determines the quantity of light that falls on the sensor. This is a design consideration than a specification of an imaging system. To capture images in low light conditions, a larger lens aperture is recommended allowing more photons to reach the sensor. However, increasing the lens aperture reduces the depth-of-field of a camera. Depth of field is a crucial consideration for an application with varying working distances, and hence a careful design is required while building a low light imaging system for such applications.
Sensitivity
Sensitivity is an indicator of the ability of an image sensor to convert incident photon energy to electrical signals. Cameras with high sensitivity allow efficient conversion of low light images to quality outputs, making it an inevitable feature for low light cameras. Responsivity is synonymous with sensitivity, and also indicates the efficiency of an imager in converting photons from a low light scene into detailed images.
Low light camera modules from e-con Systems:
- e-CAM83_CUMI415 – 4K IMX415 Low light Camera Module
- e-CAM31_MI0330_MOD – 3.4 MP Liquid Lens Camera Module
- e-CAM30A_CUMI0330_MOD – 3.4 MP Low Light Camera Module
- e-CAM220_CUMI327_MOD – Full HD IMX327 Lowlight Camera Module
- e-CAM21_CUMI290_MOD – 2MP IMX290 ultra-lowlight Camera Module
- e-CAM27_CUMI290_MOD – 2MP IMX290 ultra-lowlight Camera Module
- e-CAM20_CU0230_MOD – 2MP HDR Camera Module
