Tone Adaptation Using Weighted Expansion Exponents
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Solution Overview
Problem
Existing methods fail to effectively tone adapt images for display devices with peak luminance levels different from the high dynamic range (HDR) peak luminance level for which the HDR image was generated, particularly when the target peak luminance falls between the low dynamic range (LDR) and HDR peak luminance levels.
Innovation Solution
An image processing method that involves linear scaling of LDR luminance values, computation of expansion exponents, and interpolation to generate target luminance values suitable for a display device with a different peak luminance, using a weighted sum of HDR and LDR expansion exponents to achieve tone adaptation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If exponential inverse tone mapping is used to generate HDR images from LDR images, then the luminance range is expanded to achieve higher peak luminance levels, but the image cannot be properly displayed on devices with different peak luminance levels
Solution Approach 1:
The patent applies dynamics by making the exponent parameter adaptive rather than fixed. The exponent value is dynamically adjusted based on the target display device's peak luminance level, allowing the same LDR input image to be transformed into HDR images optimized for different display capabilities. This resolves the contradiction by enabling the system to adapt to various peak luminance requirements while maintaining the luminance expansion capability.
Solution Approach 2:
The patent changes the exponent parameter based on the target peak luminance level. By computing different exponent values corresponding to different target luminance levels, the system can transform a single LDR image into multiple HDR versions suitable for different display devices. This parameter change approach directly addresses the adaptability issue while preserving the luminance expansion benefit.
2Adaptability or versatility
If multiple HDR versions are generated for different peak luminance levels, then adaptability to different devices is improved, but computational complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-defining a set of exponent values that correspond to different target peak luminance levels. Instead of computing exponents dynamically for each device, the system prepares these exponent maps in advance, which can then be quickly selected and applied based on the target device characteristics. This reduces computational complexity during actual tone adaptation while maintaining adaptability.
Solution Approach 2:
The patent uses partial action by generating HDR images for a discrete set of predetermined peak luminance levels rather than continuously for all possible levels. This selective approach covers the most common display device categories (SDR, HDR, and various intermediate levels) without the excessive computational burden of generating HDR versions for every possible luminance level, thus balancing adaptability with computational efficiency.
Data Source
Figure 1
AI summary
This method comprises: - obtaining low dynamic range expansion exponents ELDR(p), - obtaining target expansion exponents ET(p) as a weighted sum of the high dynamic range expansion exponents EHDR(p) and of the low dynamic range expansion exponents ELDR(p), - applying obtained target expansion exponent ET(p) to low dynamic range luminance values YLDR of a low dynamic range version of the image, resulting in target luminance values YT, - building a tone-adapted version of said image based on said target luminance values YT.