Digital black level calibration device and method thereof

Abstract

The invention provides a digital black level calibration device and a method thereof, wherein the digital black level calibration device comprises a combining circuit, a digital programmable gain amplifier (PGA), and a black level feedback circuit. The combining circuit combines a digital image signal for optical black (OB) pixels and a feedback signal and outputs a digital PGA input signal. The PGA amplifies the digital PGA input signal by a PGA gain value and outputs a digital PGA output signal. The black level feedback circuit receives the digital PGA output signal and a target black level and in response outputs the feedback signal such that a black level of the OB pixels is calibrated with respect to the target black level. The programmable digital black level calibration circuit calibrates the black level in pure digital domain using signed data buses. The target black level is adjustable to a desired positive or negative value independent from the PGA gain value.

Description

technical field [0001] The present invention relates to digital imaging, and more particularly, to a digital black level calibration device and method. Background technique [0002] Digital cameras use image sensors to convert optical images received through a lens into electronic image sensor output data. In order to improve the image quality, it is necessary to calibrate the black level of the output data of the image sensor. Image sensor output data typically includes effective pixel data and optical black (OB) pixel data. OB pixel data is not illuminated pixels. First, the black level of the OB pixel data is calibrated according to the desired black level, and then the valid pixel data is corrected using the calibrated black level. [0003] figure 1 is a simplified block diagram of an analog front end (AFE) integrated circuit 11 with an analog black level calibration circuit. The AFE integrated circuit 11 includes a correlation double precision sampling (Correlated ...

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Problems solved by technology

Furthermore, since all data buses are unsigned, the minimum value of the black-level corrected data signal 35 is clamped to 0, and when a positive OB adjust signal 36 is applied, there is no comparison The value of the data signal 35 after correcting the black level of the OB adjustment signal 36 is lower

And the clamping phenomenon produces a dead zone (dead zone) in the image data, thereby reducing the quality of the image

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