在下面的例子中，我使用 3 个 foreach 循环来为 RGB 立方体着色。例如，如果红色是 0 或 255，则蓝色和绿色都应该在范围 (0,255) 内运行。目前我的代码使用的是 0,10,20，...，255。
注意：由于 foreach 任务太多，当前编译时间有点长！
\documentclass[tikz,border=3mm]{standalone}
\usepackage{tikz-3dplot}
\def\matCC{{0.257, 0.504, 0.098},%
{-0.148, -0.291, 0.439},%
{0.439, -0.368,0.071}}%
\pgfmathdeclarefunction{RGBvec}{3}{%
\begingroup%
\pgfmathsetmacro{\myY}{16+{\matCC}[0][0]*#1+{\matCC}[0][1]*#2+{\matCC}[0][2]*#3}%
\pgfmathsetmacro{\myCb}{128+{\matCC}[1][0]*#1+{\matCC}[1][1]*#2+{\matCC}[1][2]*#3}%
\pgfmathsetmacro{\myCr}{128+{\matCC}[2][0]*#1+{\matCC}[2][1]*#2+{\matCC}[2][2]*#3}%
\edef\pgfmathresult{\myCr,\myCb,\myY}%
\pgfmathsmuggle\pgfmathresult\endgroup%
}%
\begin{document}
\tdplotsetmaincoords{70}{110}
\begin{tikzpicture}[bullet/.style={circle,inner
sep=2pt,fill},line cap=round,line join=round,
RGB coordinate/.code args={(#1,#2,#3)}{\pgfmathparse{RGBvec(#1,#2,#3)}%
\tikzset{insert path={(\pgfmathresult)}}},font=\sffamily,thick]
\begin{scope}[tdplot_main_coords,scale=1/40]
\draw[-stealth] (0,0,0) coordinate (O) -- (280,0,0) coordinate[label=below:Cr] (Cr);
\draw[-stealth] (O) -- (0,280,0) coordinate[label=below:Cb] (Cb);
\draw[-stealth] (O) -- (0,0,280) coordinate[label=left:Y] (Y);
\path
foreach \r in {0,10,...,255} {
foreach \g in {0,10,...,255}{
foreach \b in {0,255} {
[RGB coordinate={(\r,\g,\b)}] node[bullet,fill={rgb,255:red,\r; green,\g; blue,\b}] (M){}
}
}
}
foreach \r in {0,255} {
foreach \g in {0,10,...,255}{
foreach \b in {0,10,...,255} {
[RGB coordinate={(\r,\g,\b)}] node[bullet,fill={rgb,255:red,\r; green,\g; blue,\b}] (M){}
}
}
}
foreach \r in {0,10,...,255} {
foreach \g in {0,255}{
foreach \b in {0,10,...,255} {
[RGB coordinate={(\r,\g,\b)}] node[bullet,fill={rgb,255:red,\r; green,\g; blue,\b}] (M){}
}
}
}
;
\path [RGB coordinate={(255,255,255)}] node[bullet,draw,fill=white] (white){}
[RGB coordinate={(0,0,0)}] node[bullet] (black){}
[RGB coordinate={(255,0,0)}] node[bullet,red] (red){}
[RGB coordinate={(0,255,0)}] node[bullet,green] (green){}
[RGB coordinate={(0,0,255)}] node[bullet,blue] (blue){}
[RGB coordinate={(255,0,255)}] node[bullet,magenta] (magenta){}
[RGB coordinate={(255,255,0)}] node[bullet,yellow] (yellow){}
[RGB coordinate={(0,255,255)}] node[bullet,cyan] (cyan){};
\draw (red) -- (black) -- (blue) -- (magenta) -- (red) -- (yellow)
-- (green) edge (black) -- (cyan) edge (blue) -- (white) edge (magenta) -- (yellow);
\draw[thin] (255,0,0) node[left]{255} -- (255,255,0) -- (0,255,0) node[above]{255}
(0,0,255) node[left]{255} -- (255,0,255) edge (255,0,0)
-- (255,255,255) edge (255,255,0) -- (0,255,255) edge (0,255,0)
-- cycle ;
\end{scope}
\end{tikzpicture}
\end{document}
输出如下：
我们如何改进它以获得连续的颜色，但不要使用 0,10，...，255 循环？
答案1
这里可以使用双线性插值。不幸的是，它实际上是为屏幕上的矩形设计的，转换它并不容易。另外pgf v.3.15 中的错误阻止我们使用符号坐标，而是使用我calc在这里使用的补丁来修复它，因为它无论如何都会被加载。
\documentclass[border=3mm]{standalone}
\usepackage{tikz}
\usepackage{tikz-3dplot}
\usetikzlibrary{shadings}
\def\matCC{{0.257, 0.504, 0.098},%
{-0.148, -0.291, 0.439},%
{0.439, -0.368,0.071}}%
\pgfmathdeclarefunction{RGBvec}{3}{%
\begingroup%
\pgfmathsetmacro{\myY}{16+{\matCC}[0][0]*#1+{\matCC}[0][1]*#2+{\matCC}[0][2]*#3}%
\pgfmathsetmacro{\myCb}{128+{\matCC}[1][0]*#1+{\matCC}[1][1]*#2+{\matCC}[1][2]*#3}%
\pgfmathsetmacro{\myCr}{128+{\matCC}[2][0]*#1+{\matCC}[2][1]*#2+{\matCC}[2][2]*#3}%
\edef\pgfmathresult{\myCr,\myCb,\myY}%
\pgfmathsmuggle\pgfmathresult\endgroup%
}%
\tikzset{RGB coordinate/.code args={(#1,#2,#3)}{\pgfmathparse{RGBvec(#1,#2,#3)}%
\tikzset{insert path={(\pgfmathresult)}}}}
\begin{document}
\tdplotsetmaincoords{70}{110}
\begin{tikzpicture}[bullet/.style={circle,inner sep=2pt,outer sep=0pt,fill},
shaded plane/.style args={(#1)--(#2)--(#3)--(#4)}{%
upper left=#4,upper right=#3,lower left=#1,lower right=#2,
tdplot_screen_coords,
insert path={
let \p1=(#1),\p2=(#2),\p3=(#3),\p4=(#4),\n1={atan2(\y2-\y1,\x2-\x1)} in
(\x1,\y1) --(\x2,\y2) --(\x3,\y3)-- (\x4,\y4)}},
line cap=round,line join=round,font=\sffamily,thick,remember picture]
%\path[use as bounding box] (-5.5,-2) rectangle (5.5,8);
\begin{scope}[tdplot_main_coords,scale=1/40,shift={(-128,-128,0)}]
\draw[-stealth] (0,0,0) coordinate (O) -- (280,0,0) coordinate[label=below:Cr] (Cr);
\draw[-stealth] (O) -- (0,280,0) coordinate[label=below:Cb] (Cb);
\draw[-stealth] (O) -- (0,0,280) coordinate[label=left:Y] (Y);
\path [RGB coordinate={(255,255,255)}] node[bullet,draw,fill=white] (white){}
[RGB coordinate={(0,0,0)}] node[bullet] (black){}
[RGB coordinate={(255,0,0)}] node[bullet,red] (red){}
[RGB coordinate={(0,255,0)}] node[bullet,green] (green){}
[RGB coordinate={(0,0,255)}] node[bullet,blue] (blue){}
[RGB coordinate={(255,0,255)}] node[bullet,magenta] (magenta){}
[RGB coordinate={(255,255,0)}] node[bullet,yellow] (yellow){}
[RGB coordinate={(0,255,255)}] node[bullet,cyan] (cyan){};
\shade[shaded plane={(red)--(black)--(green)--(yellow)}];
\shade[shaded plane={(black)--(blue)--(cyan)--(green)}];
\shade[shading angle=40,shaded plane={(green)--(cyan)--(white)--(yellow)}];
%
\path foreach \X in {red,black,blue,cyan,green,yellow,white}
{(\X) node[bullet,\X]{}};
\draw[thin] (255,255,0) -- (255,0,0) node[pos=1.1]{255}
(255,255,0) --(0,255,0) node[pos=1.1]{255}
(0,0,255) node[left]{255} -- (255,0,255) edge (255,0,0)
-- (255,255,255) edge (255,255,0) -- (0,255,255) edge (0,255,0)
-- cycle ;
\end{scope}
\end{tikzpicture}
\end{document}
