Use colormap to color axis?

From reading the documentation, it seems axes colors can only be 'uniform'.

Would there be a way to apply a colormap to an axes color property?

[Roger Breton]

Seems all I can possibly control is through the X, Y and ZColor :

set(ax, {'XColor', 'YColor', 'ZColor'}....

The default is [0.15 0.15 0.15] RGB triplet.

I don't see any 'colormap' option here... unless there is a hack? I'm about to throw the towel :(

[Image Analyst]

Why throw in the towel? Didn't my answer below do what you want?

Answer 1

[Image Analyst]

I think you'd have to use line() to draw colored line segments along the x axis:

plot(1 : 10, 'b.-', 'LineWidth', 2, 'MarkerSize', 30);
xl = xlim()
yl = ylim()
xs = linspace(xl(1), xl(2), 200);
hold on;
colorList = turbo(length(xs));
xAxisWidth = 4;
for k = 1 : length(xs)
    thisColor = colorList(k, :);
    line([xs(k), xl(end)], [0, 0], 'Color', thisColor, 'LineWidth', xAxisWidth)
end
hold off;

[Walter Roberson]

There are also File Exchange contributions to create colored lines. Some of them use patch(), some use surf(), some use plot()

plot() does not have any documented method of producing color-blended lines, but if I recall correctly there is a way to do it, probably described in Undocumented MATLAB

[Image Analyst]

Yes. Anohter method is to create a colorbar, then reshape/resize it and move it. I know Roger saw that method in a different answer. Of course if you do that, you can't then use the colorbar for its intended purpose anymore.

[Roger Breton]

Dear ImageAnalyst, you gave me ample food for thought.

Since this is a 'line', with a width of 4, is this, like, being drawn on top of the axis? I don't suppose I could use this technique to 'color' the axis of a 3D figure?

(Know that I first posted this very question, yesterday, with all my current code, screen capture and all, asking for suggestions on how to color axis using gradients but it was turned down because it contained spam or something like that?... I wrote to Matlab Central to complain but my question has not surface back yet... I'm sorry, I should have been more specific in my question but judging from your reply, demonstrated on a 2D figure, I tend to conclude that, 'coloring axis using other than a solid color' oin a 3D figure is not possible in Matlab... I'm not throwing the towel yet...)

I'll experiment with your code further and report .....

Thank you so much for you kind and patient help!

[Image Analyst]

Roger, there is a plot3() where you could plot either dots or lines along any of the axes in 3-D. I plotted lines just to be sure there were no gaps like there might be if I used dots and didn't plot them dense enough.

I also don't think multicolored axes lines are such a common desire that Mathworks would build this in, plus there are workarounds to do it. I doubt many/enough people want to do it for them to go to the trouble of having it be a standard feature.

[Walter Roberson]

https://www.mathworks.com/matlabcentral/answers/1630045-coloring-axis-with-gradients was rescued from the spam filter about 21 hours ago, and someone replied to it at that time.

[Roger Breton]

I have no idea where to go look for the reply, Walter.

Meanwhile, I analyse Image Analyst code. This is one of the most interesting and powerful feature of Matlab, to be able to step through the script one line at a time and to be able to inspect every value :

plot(1 : 10, 'b.-', 'LineWidth', 2, 'MarkerSize', 30);

xl = xlim();

yl = ylim();

% y = linspace(x1,x2,n) generates n points. The spacing between the points is (x2-x1)/(n-1)

% xs = linspace(xl(1), xl(2), 200);

% xs = linspace(xl(1), xl(2), 10);

xs = linspace(1, 10, 10);

hold on;

% turbo = colormap array

% colorList = turbo(length(xs)); % 10 Rangées x 3 double, RGB

colorList = winter(length(xs));

% j = colorList(1, :)

% colorList = [0.3 0.9 0.1]

xAxisWidth = 50;

% First coordinate, specified as a vector or a matrix.

% the first coordinate is x-axis position in data units

% the second coordinate is y-axis position in data units

% color = double RGB triplet

% line([xs(1), xl(end)], [0, 0], 'Color', colorList(1, :), 'LineWidth', xAxisWidth)

% line([1, 10], [0, 0], 'Color', colorList(1, :), 'LineWidth', xAxisWidth)

for k = 1 : length(xs)

fprintf('Itération = %i \n',k);

fprintf('ColorList = R%4.2f G%4.2f B%4.2f \n', colorList(k, 1), colorList(k, 2), colorList(k, 3))

thisColor = colorList(k, :);

fprintf('Line Origin (xs(k) x1(end)) = [%i, %i] \n', xs(k), xl(end));

fprintf('thisColor = [R%4.2f G%4.2f B%4.2f] \n', thisColor(1), thisColor(2), thisColor(3));

line([xs(k), xl(end)], [0, 0], 'Color', thisColor, 'LineWidth', xAxisWidth)

end

hold off;

I think it's a good idea. Trouble is to come up with the custom colormap in the first place... My next target for study. Thank you for all your help.

[Walter Roberson]

@Roger Breton

https://www.mathworks.com/matlabcentral/answers/1630045-coloring-axis-with-gradients#answer_875575