Merged Multiresolution Hierarchies for Shadow Map Compression

For the sake of improving the third dimension of 3D scenes, we analyze the existent real-time shadow generating algorithms, and improve the Chan’s smoothie soft shadow algorithm, make it based on shadow map, and treat with both the inner and outer penumbra. It not only effectively resolves the problems such as some algorithms can not cast shadow on itself and some are too complex, it also solves the aliasing problems of shadow mapping, and it meet the requirements of real-time in more complex scene. At last, the algorithm is emulated with DirectX, and the experimental results show the feasibility of the algorithm.

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SHADOW DETECTION FROM VERY HIGH RESOLUTON SATELLITE IMAGE USING GRABCUT SEGMENTATION AND RATIO-BAND ALGORITHMS

ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences ◽

10.5194/isprsarchives-xl-3-w2-95-2015 ◽

2015 ◽

Vol XL-3/W2 ◽

pp. 95-101 ◽

Cited By ~ 4

Author(s):

N. M. S. M. Kadhim ◽

M. Mourshed ◽

M. T. Bray

Keyword(s):

Satellite Image ◽

Visible Spectrum ◽

Urban Environments ◽

Shadow Detection ◽

Detection Methods ◽

Illumination Direction ◽

Colour Image ◽

Shadow Map ◽

Segmentation Approach ◽

Very High

Very-High-Resolution (VHR) satellite imagery is a powerful source of data for detecting and extracting information about urban constructions. Shadow in the VHR satellite imageries provides vital information on urban construction forms, illumination direction, and the spatial distribution of the objects that can help to further understanding of the built environment. However, to extract shadows, the automated detection of shadows from images must be accurate. This paper reviews current automatic approaches that have been used for shadow detection from VHR satellite images and comprises two main parts. In the first part, shadow concepts are presented in terms of shadow appearance in the VHR satellite imageries, current shadow detection methods, and the usefulness of shadow detection in urban environments. In the second part, we adopted two approaches which are considered current state-of-the-art shadow detection, and segmentation algorithms using WorldView-3 and Quickbird images. In the first approach, the ratios between the NIR and visible bands were computed on a pixel-by-pixel basis, which allows for disambiguation between shadows and dark objects. To obtain an accurate shadow candidate map, we further refine the shadow map after applying the ratio algorithm on the Quickbird image. The second selected approach is the GrabCut segmentation approach for examining its performance in detecting the shadow regions of urban objects using the true colour image from WorldView-3. Further refinement was applied to attain a segmented shadow map. Although the detection of shadow regions is a very difficult task when they are derived from a VHR satellite image that comprises a visible spectrum range (RGB true colour), the results demonstrate that the detection of shadow regions in the WorldView-3 image is a reasonable separation from other objects by applying the GrabCut algorithm. In addition, the derived shadow map from the Quickbird image indicates significant performance of the ratio algorithm. The differences in the characteristics of the two satellite imageries in terms of spatial and spectral resolution can play an important role in the estimation and detection of the shadow of urban objects.

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Shadow Map Construction using 2D Homography

International Journal of Engineering and Advanced Technology - Regular Issue ◽

10.35940/ijeat.d6480.049420 ◽

2020 ◽

Vol 9 (4) ◽

pp. 2485-2488

Keyword(s):

Computer Graphic ◽

Map Construction ◽

Shadow Map ◽

Shadow Maps ◽

The Relationship ◽

Homography Transformation

In computer graphic applications, shadow plays an important role in expressing the reality of an object. Shadow shows the relationship between objects in space. Shadow map is one of the methods that meet the demand simplification in implementation and speed. This method made an alias around the border of shading. In this paper, we proposed a method using a 2D homography transformation. This method reduces the unused area in the shadow maps, so it can help to minimize the alias. With the experiment in VanMieu Tran Bien- a Vietnamese historical place, we compare the method with others.

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