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revision 1.23 by tjl, Fri Nov 15 10:49:17 2002 UTC revision 1.24 by tjl, Fri Nov 15 11:01:04 2002 UTC
# Line 176  Color spaces: perceptually uniform Line 176  Color spaces: perceptually uniform
176    
177  \subsection{Basis textures}  \subsection{Basis textures}
178    
179    We call the textures assigned to each OpenGL texture unit {\em basis textures}.
180    
181  In order to avoid shapes or features from the basis textures becoming  In order to avoid shapes or features from the basis textures becoming
182  identifiable, the basis textures should be relatively uniform.  identifiable, the basis textures should be relatively uniform.
183  We have obtained good results with a mix of  We have obtained good results with a mix of
184  small textures with uniformly random texels,  small textures with uniformly random texels,
185  larger textures with noise or turbulence\cite{perlin-noise-intro},  larger textures with noise or turbulence\cite{perlin-noise-intro},
186  and simple geometric images (checkerboard, cone).  and simple geometric images (e.g. checkerboard).
187    
188  As for selection of basis textures for each paper, the principle of ``saving bits'' applies:  As for selection of basis textures for each paper, the principle of ``saving bits'' applies:
189  using hyperparameters for each paper to control the probabilities of  using hyperparameters for each paper to control the probabilities of
# Line 190  of one or two types will give a specific Line 192  of one or two types will give a specific
192    
193  \subsection{Texture coordinates}  \subsection{Texture coordinates}
194    
195  Basic choice: finite repeating unit or not?  Texture coordinates define the mapping of the basis textures to the paper.
196    Each basis texture is repeating, but by choosing the texture coordinates
197  Absolute scale --- sharp/blur  appropriately we can make the final paper repeating or not.
198    If the paper will be used only at relatively few magnifications, it is
199  Repeating unit  useful to use a repeating paper because of saving bits.
200    On the other hand, for user interfaces where zooming at widely different
201  {\bf tjl}  scales is desirable, a non-repeating paper can be better.
202    
203    In order to create more interesting textures, it can also be useful
204    to use repeating units for non-repeating papers --- but use more than one,
205    which are not rationally related.
206    
207    The choice of the repeating unit fixes an absolute scale to the paper.
208    The repeating unit should be relatively isotropic to avoid
209    the degeneration of textures to diagonal lines.
210    
211    After a repeating unit is fixed, there is still
212    freedom in choosing
213    textures coordinates for each texture
214    unit: any mapping of the texture is fine, as long as it repeats
215    with the selected repeating unit.
216    
217  \subsection{Register combiners}  \subsection{Register combiners}
218    

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