Auto-Exposure Circuit Digital Gain Noise Reduction
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Solution Overview
Problem
Conventional automatic exposure techniques in digital photography often result in increased noise, especially in low-light conditions, as they rely heavily on analog gain which is limited to discrete steps and cannot effectively reduce noise without compromising image brightness.
Innovation Solution
The method involves an auto-exposure circuit that adjusts aperture, shutter time, and both analog and digital gain to optimize exposure, allowing for adaptive digital attenuation of picture lightness and integrating white balancing to reduce amplification noise, using a combination of analog and digital gains to achieve desired brightness levels while minimizing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If high analog gain is used to increase signal voltage in low light conditions, then picture lightness is improved, but noise increases significantly
Solution Approach 1:
The gain function is segmented into two independent parts: analog gain (applied before ADC) and digital gain (applied after ADC). This allows the system to use low analog gain to minimize noise while using digital gain to achieve the required picture lightness, thereby resolving the contradiction between lightness and noise.
Solution Approach 2:
The digital signal processing stage acts as an intermediary between the sensor and final output. By introducing digital gain as a mediator, the system can adjust picture lightness without the noise-amplifying effect of high analog gain, as digital operations do not introduce additional sensor noise.
2Power
If analog gain is increased to compensate for low light, then signal voltage is amplified, but discrete step limitations prevent fine noise control
Solution Approach 1:
The gain control is segmented into analog and digital domains. Analog gain provides coarse adjustment with discrete steps, while digital gain provides fine-grained continuous adjustment. This segmentation enables precise noise control that was impossible with analog gain alone.
Solution Approach 2:
The patent replaces the purely mechanical/analog gain system with a hybrid system that incorporates digital signal processing. This substitution allows for continuous, precise control of gain levels without the discrete step limitations of analog systems.
3Object-generated harmful factors
If conventional AE techniques reduce maximum gain at low illumination levels, then noise is reduced, but picture lightness becomes insufficient
Solution Approach 1:
By segmenting gain into analog and digital components, the system can maintain low analog gain (reducing noise) while applying digital gain to achieve adequate picture lightness. This resolves the contradiction that forced conventional systems to choose between noise and lightness.
Solution Approach 2:
The patent changes the fundamental parameter of how gain is applied - transitioning from purely analog gain adjustment to a hybrid analog-digital approach. This parameter change enables simultaneous optimization of both noise levels and picture lightness.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces noise in both bright and low-light conditions by utilizing adjustable digital gain, providing improved noise reduction and maintaining desired image brightness levels, even when analog gain is increased, by applying negative digital gain to counteract the noise introduced by higher analog gain settings.
Implementation Method 1
The sensor may be configured to generate a digital signal in response to an optical signal
Data Source
AI summary
A camera generally including a sensor and an auto-exposure circuit is disclosed. The sensor may be configured to generate a digital signal in response to an optical signal. The auto-exposure circuit may be configured to control a lightness of a picture within the digital signal by (i) adjusting at least one among an aperture, a shutter and an analog gain and (ii) adjusting a digital gain applied to the digital signal, wherein the digital gain adaptively reduces the lightness of the picture.