Diffuse Map Shadow Removal Using Brightness Lookup Tables
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Solution Overview
Problem
Existing methods for removing shadows in three-dimensional modeling based on photogrammetry result in loss of map details, hue changes, color overflow, and color lumps, making the model unrealistic and unsuitable for various illumination conditions.
Innovation Solution
A method involving the use of average brightness difference and lookup tables to restore shadow texel colors in diffuse reflection maps, utilizing bright-side and dark-side average color lookup tables, and edge extraction to accurately remove shadows while preserving original color information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If existing shadow removal tools (Agisoft Texture Delighting, Unity De-Lighting tool) are used to remove shadows, then shadow removal is achieved, but map details are lost, hue changes occur, color overflow happens, and color lumps appear
Solution Approach 1:
The patent applies local quality by treating shadow regions and non-shadow regions differently. It identifies shadow texels based on brightness thresholds and applies shadow removal only to those specific regions, while preserving the original color information in non-shadow regions. This localized approach prevents the color distortion and detail loss that occur when applying global shadow removal algorithms.
Solution Approach 2:
The patent introduces an intermediary approach by using a lookup table (LUT) mechanism that maps shadow brightness values to restored color values. Instead of directly applying complex shadow removal algorithms, it uses the LUT as an intermediary to transform shadow regions, which simplifies the process and maintains color accuracy by preserving the original color information through the lookup table.
2Adaptability or versatility
If shadow removal is applied to diffuse reflection maps, then illumination independence is achieved, but color information is distorted and model realism is reduced
Solution Approach 1:
The patent extracts only the shadow component from the diffuse reflection map while preserving the original color information. By identifying shadow texels through brightness threshold comparison and extracting only those regions for processing, it separates the shadow effect from the underlying object color, enabling illumination independence without distorting the original color information that contributes to model realism.
Solution Approach 2:
The patent changes the parameter approach by using brightness threshold comparison to identify shadow regions and then applying specific color restoration parameters to those regions. It modifies the color values of shadow texels based on their brightness characteristics while maintaining the original color information in non-shadow regions, thus achieving illumination adaptability without compromising model realism.
Data Source
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Figure 2B~3
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AI summary
Disclosed are an image processing method and apparatus, a computer storage medium, and an electronic device, which relate to the field of image processing. The method comprises: acquiring a diffuse map, and acquiring a shadow texel, located in a shadow area, in the diffuse map (S310); querying an average color lookup table according to spatial coordinate information of the shadow texel, and according to a query result, determining an average brightness difference corresponding to the shadow texel (S320); and determining restored color information according to the average brightness difference and color information corresponding to the shadow texel, and according to the restored color information, restoring the color information of the shadow texel (S330). By means of the method, a shadow in a diffuse map can be effectively removed, such that a model can be used in scenarios with any lighting conditions.