How to give diferent colours to diferent values in a matrix?

Hi! I have a 3d matrix of 0's and 1's. I would like to plot it with scatter3 with 0's showing up black and 1's showing up white. Is that possible?

Thank you, Inês

Answer 1

[Adam]

scatter3(X,Y,Z,S,C)

The final argument there is a colour vector, of equal length to the X and Y vectors. If you don't care about the marker type you can pass in [] as the S argument.

[Inês Rodrigues]

I think I didn't understand. My matrix is 128x256x86 so I don't know where are the 0's and 1's. How can I specify the colours of the values?

[Adam]

Well, you need to collapse your matrix to a vector of X and Y values in the first place as the 3d structure does not carry any meaning in a scatter plot unless you are trying to say you want X, Y and Z to be represented as 1:128, 1:256 and 1:86 and you have a scatter plotted marker at every single point in your grid.

If your matrix is just 1s and 0s though then you can create a colour vector easily enough.

For example:

myVec = [0 0 0 1 0 1 0 1 0 1 0 0 0 1 1 1 ];

C = repmat( myVec', [1 3] );

That is specific to the case you have, since [0 0 0] is black and [1 1 1] is white so just replicating your data gives the correct colour. If you wanted different colours for the points you would have to do something a little more detailed.

[Inês Rodrigues]

I'm really sorry but I'm not understading. I have a 3d matrix with different values. I thresholded it in order to be only 0 and 1, like a mask. And now I want to visualize the result. So I want to have a 3d scatter plot with all my points, with 0's in black and 1's in white.

[Adam]

So in that case you will have to create the X, Y and Z values first. The X, Y and Z vectors that scatter3 takes as its arguments represent the points that it will plot, so you need to create these vectors in such a way that they include every (x,y,z) triplet. You should be able to do this using

doc meshgrid

but a scatter plot doesn't really seem like a suitable way of displaying such regular data filling a grid. It is unlikely you will be able to interpret much off it.