Abstract
Multi-pixel photon counting detectors can produce images in low-light environments based on passive photon counting technology. However, the resulting images suffer from problems such as low contrast, low brightness, and some unknown noise distribution. To achieve a better visual effect, this paper describes a denoising and enhancement method based on a block-matching 3D filter and a non-subsampled contourlet transform (NSCT). First, the NSCT was applied to the original image and histogram-equalized image to obtain the sub-band low- and high-frequency coefficients. Regional energy and scale correlation rules were used to determine the respective coefficients. Adaptive single-scale retinex enhancement was applied to the low-frequency components to improve the image quality. The high-frequency sub-bands whose line features were best preserved were selected and processed using a symbol function and the Bayes-shrink threshold. After applying the inverse transform, the fused photon counting image was subjected to an improved block-matching 3D filter, significantly reducing the operation time. The final result from the proposed method was superior to those of comparative methods in terms of several objective evaluation indices and exhibited good visual effects and details from the objective impression.
Highlights
Dark environments often have a small amount of natural light, such as moonlight, starlight, and atmospheric glow
The high detection efficiency and signal-to-noise ratio (SNR) of photon counting have led to its use in laser radar, quantum optics, bio-medicine, environmental radiation measurements, particle physics, high-energy physics, astronomy, and fluorescence measurements [3,4,5,6,7,8,9]
A Gaussian distribution model has been applied to the non-subsampled contourlet transform (NSCT) domain to obtain a reasonable denoising effect [28], but the model cannot remove noise that is concentrated in the highest scale sub-band
Summary
Dark environments often have a small amount of natural light, such as moonlight, starlight, and atmospheric glow. Photon counting detectors with high detection efficiency and quantum efficiency have become a topic of interest in the field of 3L imaging [2]. Avalanche excess noise is caused by the quantum effect during MPPC operation, which approximately obeys the Poisson distribution. The magnitude of it is affected by the impact ionization coefficient of electrons and holes, and is related to the position of the photo-generated and thermal-generated current. A Gaussian distribution model has been applied to the NSCT domain to obtain a reasonable denoising effect [28], but the model cannot remove noise that is concentrated in the highest scale sub-band.
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