Abstract
This paper presents an image enhancement algorithm for low-light scenes in an environment with insufficient illumination. Simple amplification of intensity exhibits various undesired artifacts: noise amplification, intensity saturation, and loss of resolution. In order to enhance low-light images without undesired artifacts, a novel digital binning algorithm is proposed that considers brightness, context, noise level, and anti-saturation of a local region in the image. The proposed algorithm does not require any modification of the image sensor or additional frame-memory; it needs only two line-memories in the image signal processor (ISP). Since the proposed algorithm does not use an iterative computation, it can be easily embedded in an existing digital camera ISP pipeline containing a high-resolution image sensor.
Highlights
As the demand for mobile devices increases, the density of a CMOS image sensor is rapidly growing
The digital pixel binning function in the conventional image signal processor (ISP) for surveillance is shown as Figure 3
In order to obtain images with different exposure values (EVs), multiple ISO values were used with a fixed aperture and shutter speed
Summary
As the demand for mobile devices increases, the density of a CMOS image sensor is rapidly growing. If the size of each pixel in the high-density image sensor becomes smaller, low-sensitivity and noise amplification problems occur, especially in low-light images. To solve this problem, many image signal processors (ISPs) adopt digital image enhancement algorithms. Since a Sensors 2015, 15 simple intensity amplification algorithm results in various undesired artifacts, sensor-based pixel binning [1,2,3,4] algorithms with noise reduction function in the image signal processor (ISP) [5,6,7] have been proposed in the literature. A basic sensor-based pixel binning method cannot avoid loss of spatial resolution, and noise reduction is still an open problem in the imaging sensor technology.
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