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revision 1.53 by tjl, Fri Nov 22 09:31:27 2002 UTC revision 1.54 by jvk, Fri Nov 22 10:18:08 2002 UTC
# Line 324  e.g.~fisheye. Line 324  e.g.~fisheye.
324    
325  \subsection{Colors}  \subsection{Colors}
326    
327  Color is the most dominant visual attribute of a paper.  Color is the most dominant visual attribute of a background.
328  Therefore, it is essential that the perception of the coloring  Therefore, it is essential that the perception of the coloring
329  of the textures is as uniform as possible. % XXX ***WHAT*** does this mean?  of the backgrounds is as uniform as possible. % XXX ***WHAT*** does this mean?
330    
331  Using multiple different colors in a texture allows  Using multiple different colors in a background allows
332  a multitude of different combinations  a multitude of different combinations
333  but too many different colors in one texture are perceived just  but too many different colors in one background are perceived just
334  as a mix of many colors, making all such textures look the same.  as a mix of many colors, making all such backgrounds look the same.
335  % XXX Connect with "random pixels" example  %XXX:
336    Connect with "random pixels" example
337    
338  Therefore, we use a small palette of carefully chosen colors for each texture,  Therefore, we use a small palette of carefully chosen colors for each background,
339  independent of the basis textures producing the shape of the final texture.  independent of the basis textures producing the shapes of the background.
340  Register combiners are used to combine the shape with the colors  Register combiners are used to combine the shape with the colors
341  as explained in the following sections.  as explained in the following sections.
342    
343  The most important constraint for the colors is readability:  Black text should have good contrast with the background.
344  black text must have good contrast with the texture.  %The most important constraint for the colors is readability:
345  % XXX This is our CHOICE for a goal, not an absolute one.  %% XXX This is our CHOICE for a goal, not an absolute one.
346  Additionally, the colors should be perceptually uniformly distributed  Additionally, the colors should be perceptually uniformly distributed
347  and ``balanced'' to avoid overloading of color perception.  and ``balanced'' to avoid overloading of color perception.
348  % "Overloading"?  % "Overloading"?
# Line 349  and ``balanced'' to avoid overloading of Line 350  and ``balanced'' to avoid overloading of
350  Usually color perception is divided to lightness, hue,  Usually color perception is divided to lightness, hue,
351  and saturation (the chromatic purity), which are nonlinearly  and saturation (the chromatic purity), which are nonlinearly
352  related to the usual RGB values.  related to the usual RGB values.
353  The are many nonlinear color spaces, such as CIE $L^*a^*b^*$  A color space is called perceptually uniform, if the Euclidian
354  \cite{cie86colorimetry},  distance of coordinates approximately corresponds to the
355  designed to represent the perceived components of color  perceived difference of color.
356  on a uniform scale.  For example, the CIE $L^*a^*b^*$ \cite{cie86colorimetry}
357    color space is reasonably perceptually uniform.
358    
359  % Uniform?  % Uniform?
360  %  1) define term  %  1) define term
361  %  2) not really uniform; it's MORE uniform than RGB but not  %  2) not really uniform; it's MORE uniform than RGB but not
# Line 361  on a uniform scale. Line 364  on a uniform scale.
364  To address readability, we only use colors with the CIE $L^*$  To address readability, we only use colors with the CIE $L^*$
365  lightness value over 80 (percent of maximum).  lightness value over 80 (percent of maximum).
366  % Mention screen gamma earlier, maybe here.  % Mention screen gamma earlier, maybe here.
 However, because the texture shapes should also be visible,  
 we use one half dark colors and one half light colors in the  
 range to have some contrast for the shapes.  
 % Mention unpleasant visual effect from textures with only  
 % chroma changes. Having contrast makes shapes distinguishable  
 Even though the register combiners interpolate linearly between  
 the colors in the palette, the lightness of an intermediate  
 color is still between the two colors, because perceived  
 lightness is a monotonous function of luminance.  
 % Doesn't really need to be said here; it's what people  
 % will naturally assume.  
367  For correct computation of the color lightness,  For correct computation of the color lightness,
368  it is essential that the display gamma is adjusted properly  it is essential that the display gamma is properly adjusted
369  for linear RGB reproduction.  for linear RGB reproduction.
370  % Onko lineaarinen *varmasti* oikea LAB-muunnokselle?  % Onko lineaarinen *varmasti* oikea LAB-muunnokselle?
371    Because the shapes should also be distinguishable,
372    we use one half dark colors and one half light colors in the
373    range to have some contrast for the shapes.
374    This avoids the unpleasant, blurry appearance of backgrounds with only
375    chroma changes in colors.
376    %Having contrast makes shapes distinguishable
377    
378    %Even though the register combiners interpolate linearly between
379    %the colors in the palette, the lightness of an intermediate
380    %color is still between the two colors, because perceived
381    %lightness is a monotonous function of luminance.
382    %% Doesn't really need to be said here; it's what people
383    %% will naturally assume.
384    
385  To have balanced colors, we choose the hues from a distribution  To have balanced colors, we choose the hues from a distribution
386  % To have: huonoa englantia  % To have: huonoa englantia
387  concentrated on one random hue with a random variance and  concentrated on one random hue with a random variance and
388  saturations chosen from an ad hoc distribution.  saturations chosen from an ad hoc distribution.
389  This produces related colors with high probability, but still  This produces related colors with high probability, but still
390  allows flashy palettes to occur occasionally.  allows motley palettes to occur occasionally.
 % flashy? flashy = hienosteleva...  
 % motley parempi?  
391    
392  Because the $a^*b^*$ plane of the CIE $L^*a^*b^*$ color space seems to  Because the $a^*b^*$ plane of the CIE $L^*a^*b^*$ color space seems to
393  have too large angle of blue for light colors,  have too large angle of blue for light colors,

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