Black-Level Correction Using Look-Up Table for Image Sensors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Digital camera sensors experience varying black levels due to analog gain and exposure time, which can lead to inaccuracies in image data, as these levels are not constant across different spatial locations, affecting the quality of the final image.
Innovation Solution
A method and apparatus for black-level correction using a look-up table that accounts for analog gain, exposure time, and spatial location variations, allowing for precise adjustment of raw image data through interpolation or extrapolation of measured black levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed black level normalization is applied in the camera sensor, then the circuitry is simple, but the black level accuracy deteriorates when analog gain or exposure time changes
Solution Approach 1:
The patent applies preliminary action by pre-measuring and storing black level values in a look-up table for various combinations of analog gain and exposure time settings. During image capture, the system simply retrieves the appropriate correction value from the pre-computed table based on current settings, avoiding complex real-time calculations while maintaining high accuracy across different operating conditions.
Solution Approach 2:
The patent utilizes parameter changes by creating a multi-dimensional look-up table that stores black level correction values for different combinations of analog gain parameters and exposure time parameters. This allows the system to adapt to changing operational parameters without requiring complex real-time computation, simply by indexing into the pre-computed table with the current parameter values.
2Measurement precision
If black level is measured at every pixel location, then the correction accuracy is improved, but the measurement time and data processing load increase
Solution Approach 1:
The patent applies segmentation by dividing the image sensor into multiple regions or zones and measuring black levels at representative sampling points within each zone. Instead of measuring every pixel, the system captures dark frames, extracts black level values from strategically selected sampling locations, and uses these segmented measurements to construct a spatially-varying correction map that is applied across the entire image.
Solution Approach 2:
The patent uses copying by measuring black levels at a limited number of sampling locations and then interpolating or extrapolating these measurements to estimate black levels at all other pixel locations. The correction values from sampled points are copied and propagated to surrounding pixels through interpolation algorithms, significantly reducing measurement time while maintaining spatial accuracy.
3Measurement precision
If the look-up table includes all possible combinations of analog gain and exposure time, then the correction accuracy is maximized, but the memory requirements increase
Solution Approach 1:
The patent applies dynamics by implementing a hierarchical or adaptive look-up table structure that can dynamically adjust its resolution based on actual usage patterns. The system may use coarser sampling for parameter combinations that are rarely used and finer sampling for commonly used settings. Additionally, the look-up table can be dynamically generated or updated based on observed operational patterns, allocating memory resources efficiently while maintaining accuracy for critical parameter combinations.
Data Source
AI summary
The black level in raw image data captured from an image sensor does not always stay fixed at a constant level, but may change as a function of the analog gain and exposure time and may vary from one spatial location of the pixels to another. To carry out black-level correction on the raw image data, the black level of each of the color components is measured at one or more sampling locations. A look-up table is generated based on the measured black levels and a computation module is used to carry out black-level correction based on the information stored in the look-up table. The look up table may have information indicative of the analog gain level and the exposure time and the variations of black-levels in different spatial locations.