How to crate a two direction colorbar?

Hi,

I am using scatter to generate a 2-D plot. My y-axis values range between, let's say, ylim([-100 100]). The direction of the colorbar, in the jet color scale, will be "dark blue" for -100 up to "dark red" for 100. Is there any way I can have a double direction colorbar centered around zero? For instance, 0 will be the "dark blue", while -100 and 100 will be the "dark red". Of course the colors inbetween will correspond to the values between [0 100] and [-100 0].

Answer 1

[Image Analyst]

Sure. Try this:

numPoints = 500;
y = -100 + 200 * rand(1, numPoints);
x = 10 * rand(1, numPoints);
% Assign colors
cm = [flipud(jet(128)); jet(128)];
% Make 200 long.
cm = imresize(cm, [200, 3]);
markerColors = zeros(length(y), 3);
for k = 1 : length(y)
	thisValue = round(y(k) + 100);
	if thisValue < 1
		thisValue = 1;
	elseif thisValue > size(cm, 1)
		thisValue = size(cm, 1);
	end
	markerColors(k, :) = cm(thisValue, :);
end
scatter(x, y, 35, markerColors, 'filled');
% Put a line at the x axis
grid on;
line(xlim, [0, 0], 'Color', 'k', 'LineWidth', 2);

[MichailM]

The problem is with the appearance of the colorbar on the right side. The color of the points is centered around the zero horizontal axis although the colorbar is not. Below is an example:

I try to achieve something like this

[Image Analyst]

Try adding the colormap and colorbar commands:

numPoints = 500;
y = -100 + 200 * rand(1, numPoints);
x = 40 * rand(1, numPoints);
% Assign colors
cm = [flipud(jet(128)); jet(128)];
% Make 200 long.
cm = imresize(cm, [200, 3]);
cm(cm>1) = 1;
cm(cm<0) = 0;
markerColors = zeros(length(y), 3);
for k = 1 : length(y)
	thisValue = round(y(k) + 100);
	if thisValue < 1
		thisValue = 1;
	elseif thisValue > size(cm, 1)
		thisValue = size(cm, 1);
	end
	markerColors(k, :) = cm(thisValue, :);
end
scatter(x, y, 35, markerColors, 'filled');
% Put a line at the x axis
grid on;
line(xlim, [0, 0], 'Color', 'k', 'LineWidth', 2);
colormap(cm);
numTicks = 21;
tickNumbers = linspace(0, 1, numTicks)
for k = 1 : numTicks
	tickLabels{k} = sprintf('%.1f', -100 + 200 *tickNumbers(k));
end
colorbar('Ticks', tickNumbers, 'TickLabels', tickLabels);

[MichailM]

That worked! Thank you very much!