Luminance Stretching Control for Video Display Devices
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Solution Overview
Problem
Conventional HDR technologies can degrade video quality by causing 'black float' and failing to maintain high contrast when uniformly increasing screen luminance, especially in videos with dark areas, as they do not effectively control luminance stretching based on the video's state.
Innovation Solution
A video display device with a control portion that detects light-emitting parts of the video signal, adjusts the backlight luminance using control curves, and divides the image into areas to change lighting rates based on tone values, reducing luminance in non-light-emitting parts to enhance contrast and prevent 'black float'.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If uniform luminance stretching is applied to increase screen brightness, then the perceived brightness and contrast are improved, but black float occurs and video quality degrades in dark areas
Solution Approach 1:
The patent applies different luminance stretching strategies to different regions of the video based on their characteristics. Bright areas undergo luminance stretching to enhance perceived brightness and contrast, while dark areas have their luminance reduced or maintained to prevent black float. This local differentiation resolves the contradiction by allowing brightness enhancement where beneficial while preserving video quality where uniform stretching would cause degradation.
Solution Approach 2:
The video content is segmented into different luminance regions (bright areas and dark areas) with distinct processing rules. The control portion separates the treatment of these regions, applying luminance stretching selectively rather than uniformly across the entire screen. This segmentation enables the system to achieve high brightness in luminous parts while maintaining proper contrast in dark parts, preventing black float.
2Ease of operation
If HDR is operated under constant conditions, then the processing is simple, but the quality of videos with dark areas degrades due to black float
Solution Approach 1:
The patent transitions from constant HDR operation to dynamic HDR operation where processing parameters change based on video content characteristics. The control portion continuously analyzes video luminance distribution and adjusts processing parameters in real-time, switching between different control curves based on whether the current frame contains predominantly bright or dark areas. This dynamic adaptation maintains video quality across varying content types while preserving operational simplicity through automated control.
3Measurement precision
If luminance stretching is applied to emphasize light emitting parts, then contrast feeling is improved, but black float occurs when applied to videos with large black areas
Solution Approach 1:
The patent applies luminance stretching selectively to light-emitting parts of the video while applying different processing to dark areas. By analyzing video luminance distribution and identifying regions with significant black areas, the system applies contrast enhancement only where it benefits the image quality, while reducing or eliminating luminance stretching in dark regions to prevent black float. This local differentiation resolves the contradiction between contrast improvement and black float prevention.
Data Source
AI summary
A light emission portion of a video signal is detected, and the display intensity of the light emission portion is enhanced for emphasis display. At this moment, the intensity stretch amount is controlled in accordance with a status of video black display, thereby increasing the feeling of brightness and hence improving the video quality. An area-active-control/luminance-stretching portion stretches and increases the intensity of a backlight portion on the basis of an index related to a brightness calculated, on the basis of a predetermined condition, from the input video signal, and lowers the video signal intensity of the non-light emission part excluding the light emission part. At this moment, the area-active-control/luminance-stretching portion changes, in accordance with a black display amount detected by a black detection portion, a control curve that defines the relationship between the index related to the brightness and the stretch amount.