MATLAB: How to set colors in quiver (2D)

colorquiver

Hi, im using the quiver function to plot arrows on a profile

so i want that the arrows which are turning inwards to be colored in a different color (blue). Also, i have a vector telling me which of them is turning inwards.

how can i do that?

thanks, Noa

Best Answer

I would separate the elements which are turning inward vs outward since you have a vector of indices and use two different calls to quiver() with the plot held on.

Then you can use

 quiver(x,y,px,py,'color',[0 0 1])

In other words, use the 'color' linespec to color them blue. For example:

 [x,y] = meshgrid(-2:.2:2,-1:.15:1);
 z = x .* exp(-x.^2 - y.^2); [px,py] = gradient(z,.2,.15);
 contour(x,y,z), hold on
 indices = 11:21;
    quiver(x(:,indices),y(:,indices),px(:,indices),py(:,indices),'color',[0 0 1]);
quiver(x(:,1:10),y(:,1:10),px(:,1:10),py(:,1:10),'color',[1 0 0]);

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MATLAB: Changing color of the Matlab plot at different ranges

Try this:

indexes = yValues > 600;
plot(x(~indexes), y(~indexes), 'b.', 'MarkerSize', 10); % Plot in blue first.
hold on;
plot(x(indexes), y(indexes), 'r.', 'MarkerSize', 10); % Plot in red next.

MATLAB: How to draw a Lab* colour space or HSV colour space (2D)

As commented in your question, note that you're only plotting one slice of the 3D colour space.

Of course, your original code doesn't work, you end up doing

pcolor(x, y, thg);

so you're only plotting the hue (angle) against x and y. There's no saturation or value information in your plot. You then apply a colour map called hsv whose colours are derived from the hsv cylinder, but in no way does it mean you've done any conversion to/from hsv. The whole idea is flawed.

Here is how I'd do it:

%inputs:
%plotradius: the plot radius of the disk. Image will be 2*plotradius+1 x 2*plotradius+1
%plotvalue:  the Value at which the slice of the HSV cylinder is to be taken. In the range 0-1
plotradius = 100;
plotvalue = 1;
[x, y] = meshgrid(-plotradius:plotradius);  %get x,y coordinates of pixels in image
[hue, saturation] = cart2pol(x, y);  %convert to angle, radius. Angle is the hue, radius is the saturation in the HSV cylinder
hue = (hue + pi) / (2*pi); %rescale from -pi:pi to 0:1 since matlab use 0:1 for the range of the hue
saturation = saturation / plotradius;  %rescale saturation to range 0:1. Not that anything above 1 is outside the cylinder
value = ones(size(hue)) * plotvalue;  %set value constant for all points in the disk
%now set points outside the disk (saturation >1) to white. That'd be a value of 1 and saturation of 0. hue doesn't matter
outsidedisk = saturation > 1;
saturation(outsidedisk) = 0;
value(outsidedisk) = 1;
%finally, convert hsv to rgb and plot
rgb = hsv2rgb(cat(3, hue, saturation, value));
imshow(rgb);

Best Answer

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MATLAB: Changing color of the Matlab plot at different ranges

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