Binning is a crucial feature of scientific cameras, especially in applications with low light such as chemiluminescence western blotting. Binning increases the sensitivity and signal-to-noise ratio (SNR), allowing for improved image quality, more rapid acquisition times, and spatial resolution to be traded for enhanced sensitivity.
The implementation of binning varies between Charge-Coupled Device (CCD) and Complementary Metal-Oxide Semiconductor (CMOS) sensors, resulting in performance differences.
Binning Basics
Individual pixels in a camera sensor collect photons of light, converting them into electrical signals, which are then digitized into an image.
Binning combines adjacent pixels signals into a single, larger, effective pixel called a superpixel. This enhances sensitivity and reduces exposure times while sacrificing spatial resolution.
The figure below demonstrates this concept using rain gathering in buckets. Larger buckets capture more raindrops; similarly, larger pixels collect more light, increasing sensitivity.
Image Credit: Synoptics Ltd
Difference Between CCD and CMOS Sensors
Due to the architectural differences between CCD and CMOS sensors, distinct approaches to binning are required, affecting performance differently.
In a CCD sensor, incident light is converted into electrical charge transferred across the sensor and read out sequentially. As a result, binning is performed ‘on-chip’. Conversely, CMOS sensors convert light into electrical signals at each pixel, and binning is performed digitally after readout.
Image Credit: Synoptics Ltd
The advantage of CCD sensors' method of converting light into electrical charge and transferring it across the sensor is that it minimizes noise from the readout amplifier. This is because the signal is read out only once after binning, reducing potential interference. CMOS sensors employ a photodiode and amplifier at each pixel, meaning individual signals are amplified and digitized at the pixel before binning.
As a result, readout noise is introduced at each pixel, meaning CMOS binning does not achieve the same SNR improvements as CCD binning. The per-pixel noise of CMOS binning is continuously improving. However, CCD technology remains the superior method.
The table below outlines the major differences between CCD and CMOS binning.
Source: Synoptics Ltd
Conclusions
Binning is a vital feature for enhancing camera performance, particularly in scientific imaging applications. Binning works particularly well in CCD sensors due to the combining of pixel charges at the sensor level before readout. This significantly improves the SNR, making CCDs the perfect choice for low-light applications where sensitivity and low noise are paramount, such as chemiluminescence western blotting.
Despite advances in CMOS technology, CCD sensors are currently preferred in low-light applications.
This information has been sourced, reviewed and adapted from materials provided by Synoptics Ltd.
For more information on this source, please visit Synoptics Ltd.