Block-Based Contrast Pre-Calculation for Fast Autofocus
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Solution Overview
Problem
Contrast detection autofocus in cameras is slower and less accurate than phase detection autofocus due to its reliance on processing multiple frames to determine focus distance and calculate contrast information, which introduces significant latency and limits its ability to define custom autofocus zones dynamically.
Innovation Solution
An apparatus and method that utilize an image processor to form image characteristics for blocks of a frame, calculate image parameters by combining characteristics within predefined zones, and a focus controller to derive a measure of focus for selected frame areas, allowing for dynamic focus control with reduced latency and improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If contrast detection autofocus processes multiple frames to determine focus distance and calculate contrast information, then focus accuracy is improved, but processing time and latency increase significantly
Solution Approach 1:
The patent pre-calculates and stores contrast information for multiple blocks in the image during the image processing stage, before autofocus is needed. This preliminary computation stores contrast values for numerous blocks across the image, so when autofocus operation is required, the system can immediately retrieve and combine these pre-computed values without performing intensive processing at that moment, thus resolving the contradiction between accurate measurement and time loss
Solution Approach 2:
The patent divides the image into multiple blocks and pre-calculates contrast information for each block independently. This segmentation allows the system to store contrast data for many small regions rather than processing the entire image at once during autofocus operations. The focused area contrast is then derived by combining relevant pre-computed block contrasts, significantly reducing processing time while maintaining focus accuracy
2Adaptability or versatility
If contrast detection autofocus processes images to identify focus zones dynamically, then adaptability is improved, but processing complexity and time increase
Solution Approach 1:
The patent performs preliminary processing to identify potential focus zones and calculate contrast information for multiple image blocks before the actual autofocus operation. Face detection and focus zone identification are completed in advance, with contrast values pre-computed for all relevant blocks. This preliminary action enables the system to adapt to different scenes and identify custom focus zones without adding complexity during the critical autofocus execution phase
Solution Approach 2:
The patent creates a simplified representation of the image by dividing it into blocks with pre-computed contrast values. Instead of processing the full-resolution image during autofocus operations, the system works with this block-based copy that contains essential contrast information. This copying approach enables dynamic focus zone selection and adaptability while significantly reducing processing complexity
Data Source
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AI summary
Apparatus for controlling the focus of a camera arranged to capture a sequence of frames, the apparatus comprising: an image processor configured to: form an image characteristic for a plurality of blocks of a first frame, each block comprising one or more pixels of the first frame; and calculate an image parameter for each block by combining the image characteristics of blocks lying within a predefined zone relative to that block; and a focus controller configured to derive a measure of focus for a selected frame area of the first frame by identifying a set of blocks whose respective predefined zones, when combined, substantially represent the selected frame area, and forming a measure of focus for the selected frame area by so combining the image parameters of the set of blocks; wherein the focus controller is configured to generate a signal for controlling camera focus in dependence on the measure of focus formed for the selected frame area of the first frame.