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"? |
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 |
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, |