74 |
|
|
75 |
Additionally, the entropy of the feature vectors over the distribution |
Additionally, the entropy of the feature vectors over the distribution |
76 |
of textures should be maximized. The distribution should contain |
of textures should be maximized. The distribution should contain |
77 |
occurrences as many different features as possible, and the features |
occurrences of as many different features as possible, and the features |
78 |
should be distributed independently from each other. |
should be distributed independently from each other. |
79 |
|
|
80 |
However, because of the limited spatial resolution of the feature |
However, because of the limited spatial resolution of the feature |
81 |
vector, in any {\em single} texture, only a limited range of features |
vector, in any *single* texture, only a limited range of features |
82 |
should be used. |
should be used. |
83 |
|
|
84 |
In a sense, the model of perception should be *inverted* in order to |
In a sense, the model of perception should be *inverted* in order to |
88 |
orthogonal (e.g. colors of neighbouring pixels) should be correlated |
orthogonal (e.g. colors of neighbouring pixels) should be correlated |
89 |
so as to maximize the entropy. |
so as to maximize the entropy. |
90 |
|
|
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|
91 |
An important point is generating the backgrounds is that the texture |
An important point is generating the backgrounds is that the texture |
92 |
appearance should have *no correlation* with any attribute or content |
appearance should have *no correlation* with any attribute or content |
93 |
of the document so that the textures of any hyperlinked documents are |
of the document so that the textures of any hyperlinked documents are |
94 |
similar only by chance. |
similar only by chance. |
95 |
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|
96 |
|
Hardware-accelerated implementation |
97 |
|
=================================== |
98 |
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|
99 |
One major goal for the implementation is to support complicated |
One major goal for the implementation is to support complicated |
100 |
mappings between paper and screen coordinates, such as fisheye |
mappings between paper and screen coordinates, such as fisheye |
111 |
GL_ARB_fragment_program once suitable hardware and Linux drivers |
GL_ARB_fragment_program once suitable hardware and Linux drivers |
112 |
emerge. |
emerge. |
113 |
|
|
|
Hardware-accelerated implementation |
|
|
=================================== |
|
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|
114 |
Colors |
Colors |
115 |
------ |
------ |
116 |
|
|
|
Color is the most dominant visual attribute of a texture. Therefore, |
|
|
it is essential that the overall colors of the backgrounds are |
|
|
maximally diverse with respect to color perception. However, we come |
|
|
again to the number-of-different-features arguments discussed earlier: |
|
|
too many different colors in a *single* background are perceived just |
|
|
as a mix of many colors, making all such backgrounds look the same. |
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|
117 |
To maintain recognizability, we use a small palette of colors for each |
To maintain recognizability, we use a small palette of colors for each |
118 |
paper, selected randomly from a heuristic distribution. The final |
paper, selected randomly from a heuristic distribution. The final |
119 |
image contains convex combinations of the palette colors. |
image contains convex combinations of the palette colors. |
153 |
built from these textures and the corresponding HILO |
built from these textures and the corresponding HILO |
154 |
textures for offsetting. |
textures for offsetting. |
155 |
|
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|
Texture shading |
|
|
--------------- |
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|
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|
156 |
On the NV25 architecture, the texture accesses can be customized |
On the NV25 architecture, the texture accesses can be customized |
157 |
further by the use of texture shading: the texture coordinates used by |
further by the use of texture shading: the texture coordinates used by |
158 |
a texture unit can be made to depend on the result of a previous |
a texture unit can be made to depend on the result of a previous |