TikZ: add blur and shade on a curve

Question

I have the following curve from a previous thread:

\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
    \draw [cyan,line width=1mm] (0,0) .. controls (3,5) and (6,-1) .. (7,2)    ;
\end{tikzpicture}
\end{document}

I would like to add 2 effects (separately):

I would like to "blur" the curve (i.e., to convolve the image with a 2-D Gaussian kernel).
I would like to add some shading. More precisely I would like the colour of the curve to progressively become white (or preferably transparent, but white will do) in some areas.

I would some documentation for the shading library but nothing for curves (only areas).

Many thanks in advance

One idea for the shading would be to trasform your curve into an area. — SebGlav, Nov 03 '23 at 13:38
Does https://tex.stackexchange.com/questions/244650/glowing-path-in-tikz help? — cfr, Nov 03 '23 at 17:19
@cfr do you meen the loop to plot multiple curves with different width and shades of black? I love it! I will implement it and update the thread. — Andros, Nov 03 '23 at 19:15
Does https://tex.stackexchange.com/questions/134283/tikz-shading-a-path-without-any-filling help? EDIT: https://tex.stackexchange.com/questions/337898/how-do-i-use-spath3-package-to-shading-a-path probably better. EDIT EDIT: https://tex.stackexchange.com/questions/566963/tikz-shading-a-path-fade-no-fill-sty-does-not-work-as-previously-oct-2020/567029#567029 is the most recent? — cfr, Nov 03 '23 at 20:38

cfr · Answer 1 · 2023-11-04T14:47:34.220

Using fade-no-fill.sty from Hotschke and Andrew Stacey for the shading and percusse's method for blurring, a shaded and blurred path can be drawn.

\documentclass{standalone}
\usepackage{tikz}
% ateb: https://tex.stackexchange.com/a/700367/
% fade-no-fill o:
% ateb Hotschke updated gan Andrew Stacey: https://tex.stackexchange.com/a/567029/
%\url{https://tex.stackexchange.com/a/327713/86}
\usepackage{fade-no-fill}
\begin{document}
\begin{tikzpicture}
  \foreach \x [evaluate=\x as \xc using 0.5100ln(10/\x)] in {10,9.9,...,1}{
    \path [fade path but don't fill={line width=\x*1pt,transparent!0}{left color=cyan!\xc,right color=magenta!\xc}] (0,0) .. controls (3,5) and (6,-1) .. (7,2)    ;
  }
\end{tikzpicture}
\end{document}

Note that you would not want to use this too often as it is s-l-l-o-o-o-w.

Edit

The code works OK for me in Beamer, too.

\documentclass{beamer}
\usepackage{tikz}
% ateb: https://tex.stackexchange.com/a/700367/
% fade-no-fill o:
% ateb Hotschke updated gan Andrew Stacey: https://tex.stackexchange.com/a/567029/
%\url{https://tex.stackexchange.com/a/327713/86}
\usepackage{fade-no-fill}
\begin{document}
\begin{frame}
  \begin{tikzpicture}
    \foreach \x [evaluate=\x as \xc using 0.5*100*ln(10/\x)] in {10,9.9,...,1}{
      \path [fade path but don't fill={line width=\x*1pt,transparent!0}{left color=cyan!\xc,right color=magenta!\xc}] (0,0) .. controls (3,5) and (6,-1) .. (7,2)    ;
    }
  \end{tikzpicture}
\end{frame}
\end{document}

Note that I'm using the second version of the sty from https://tex.stackexchange.com/a/567029/ i.e. the updated one added in July 2021 by Andrew Stacey, modified in light of changes to spath3.

Or if you do want to use many, you may be interested in memoize ... ;). — cfr, Nov 03 '23 at 21:42
Thanks @cfr. I created a modified version of fade-no-fill.sty file but using spath3 as spath is depreciated, using https://tex.stackexchange.com/questions/337898/how-do-i-use-spath3-package-to-shading-a-path but unfortunately I get a lot of errors when compiling — Andros, Nov 04 '23 at 09:15
I worked it out on a standalone document, but for some reason it produces a blank image in my Beamer document — Andros, Nov 04 '23 at 13:49
@Andros I used the sty from https://tex.stackexchange.com/a/567029/. The second one in that answer - not the first. That uses spath3 and was updated in July 2021. — cfr, Nov 04 '23 at 14:42
@Andros I've added the code and output for my Beamer test. See edit above. — cfr, Nov 04 '23 at 14:48

score 1 · Answer 2 · answered Nov 03 '23 at 19:51

So I have implemented that solution from here

\begin{tikzpicture}
    \foreach \x[evaluate={\xc=0.5*100*ln(10/\x);}] in {10,9.9,...,1}{
        \draw [draw=cyan!\xc,line width=\x*1pt] (0,0) .. controls (3,5) and (6,-1) .. (7,2)    ;
    }
\end{tikzpicture}

which produce this acceptable output. However I don't understand why using cyan!\xc instead of draw=cyan!\xc returns

Package color Error: Argument `1.02026' not in range [0,1]. ^^I}

as \xc is supposed to be between 0 and 100...

I still have no solution for shading the curve...

I think it is trying to interpret the colour using a different colour model. Why it is doing that I'm not sure. — cfr, Nov 03 '23 at 21:45

TikZ: add blur and shade on a curve

2 Answers2

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