Web Camera Video Capture Adaptive Frame Rate Control
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Solution Overview
Problem
USB 1.1's limited data transfer rate causes image discontinuity in video captured by web cameras, requiring effective compression methods to prevent this, but existing lossy compression techniques trade off image quality for compression ratio, leading to suboptimal results.
Innovation Solution
A video image capturing and displaying method that employs adaptive frame rates and dual compressing engines, including a sequential line skipping unit and a sequential line passing unit, to optimize compression and decompression, using techniques like discrete cosine transform, differential pulse code modulation, and wavelet compression, with a frame rate controller determining the optimal frame rate based on display quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If image compression is applied to reduce data size for USB 1.1 transfer, then data transfer feasibility is improved, but image quality deteriorates due to lossy compression
Solution Approach 1:
The patent implements dynamic frame rate adjustment based on USB buffer status. When the buffer is full, the frame rate is reduced to prevent overflow and maintain image quality. When buffer space is available, the frame rate increases to improve video smoothness. This dynamic adaptation resolves the contradiction by adjusting temporal resolution rather than spatial compression, avoiding quality degradation.
Solution Approach 2:
The system changes the frame rate parameter dynamically based on USB transfer conditions and buffer status. Instead of using fixed lossy compression that degrades image quality, the system adjusts the temporal sampling rate (frames per second) to match the USB 1.1 data transfer capability, thereby maintaining image quality while ensuring feasible data transfer.
2Productivity
If high frame rate is used to prevent image discontinuity, then video smoothness is improved, but data transfer burden increases beyond USB 1.1 capability
Solution Approach 1:
The patent employs dynamic frame rate control that adapts to USB buffer status. The frame rate is adjusted in real-time based on whether the USB buffer is full or has available space. This dynamic approach ensures video smoothness is optimized within the constraints of USB 1.1 data transfer capability, preventing both image discontinuity and data overflow.
Solution Approach 2:
The system implements feedback control by monitoring the USB buffer status and adjusting the frame rate accordingly. When the buffer is full, feedback triggers a frame rate reduction to prevent data loss. When buffer space is available, feedback allows increasing the frame rate to improve video smoothness. This closed-loop control resolves the contradiction between video quality and data transfer burden.
3Productivity
If complex compression algorithms are used to achieve higher compression ratios, then compression efficiency is improved, but device complexity increases
Solution Approach 1:
The patent extracts the compression function from the web camera itself and relocates it to the host computer. The USB device driver on the host performs the compression of image data before transferring to the operating system. This extraction reduces the complexity of the web camera hardware while maintaining efficient compression, as the host computer has greater processing capabilities.
Solution Approach 2:
The USB device driver acts as an intermediary between the web camera hardware and the operating system. It handles the compression task in this intermediate layer, allowing the camera to remain simple while achieving efficient compression through the driver's processing capabilities. This mediator approach resolves the contradiction by shifting complexity to an appropriate layer in the system architecture.
Data Source
AI summary
A video image capturing and displaying method for a web camera is disclosed. The method includes the steps of: capturing a video image consisting of a time series of image frames, at an adaptive frame rate, each image frame comprising a plurality of sequential lines of pixels; compressing the captured video image with one of at least a first compressing mode and a second compressing mode; decompressing the compressed video image corresponding to the compressing mode; storing, in a buffer, the decompressed video image which is not displayed in time; and displaying the video image based on the stored video image and the decompressed video image, wherein the adaptive frame rate in the capturing step is determined according to the display quality of the video image being displayed in the displaying step.