Is 2d colormap supported by matlab?

Generally in matlab we use 1D gradient colormap as

How do we use colormap like this

[Stephen23]

A 2D "colormap" is called an "image".

[Ray Lee]

I meant to apply this colormap to image, not plot this colormap as image

[Stephen23]

A colormap is one dimensional, and scales to values. If you want to map by multiple dimensions, then use interpolation, indexing, mapping, or something similar.

[Image Analyst]

Your indexed or grayscale image has a single value (per pixel). This value is then used as an index into a 1-D colormap to basically turn a gray scale value into a color. If your colormap has two dimensions, then exactly what would you use as indexes to pick the color from your 2-D colormap? Of course the gray level will be one index, but what would you use as the second index? All you have is the graylevel, which can be used to select the column to use from your 2-D colormap, unless you're supplying some other attribute to select the row of your 21-D colormap.

[Ray Lee]

@ImageAnalyst Yes, you are right. The color and the brightness represent two data sets. I found an example here

[Stephen23]

@Ray Lee: as an aside, you really really should avoid using the awful JET/RAINBOW colormap. The reasons have been discussed in detail on the internet, and also here:

https://blogs.mathworks.com/steve/2014/10/13/a-new-colormap-for-matlab-part-1-introduction/

https://blogs.mathworks.com/steve/2014/10/20/a-new-colormap-for-matlab-part-2-troubles-with-rainbows/

https://blogs.mathworks.com/steve/2014/11/12/a-new-colormap-for-matlab-part-3-some-reactions/

https://blogs.mathworks.com/steve/2014/12/10/a-new-colormap-for-matlab-part-4-the-name/

The new default colormap parula is a significant improvement, and you can also find other colormaps on FEX, ready for you to download:

https://www.mathworks.com/matlabcentral/fileexchange/?term=perceptually+uniform

Answer 1

[Image Analyst]

Ray, if you have two parameters, air pressure and frequency, you can't use a colormap and you'll have to create an RGB image instead. You can get the color like this, assuming air pressure and frequency are the row and column of your "colormap" image:

for col = 1 : columns
    for row = 1 : rows
        thisColor = colormap2D(frequency(row, column), pressure(row, column), :) % A 1-by-3 vector
        rgbImage(row, column, :) = thisColor;
    end
end

So it has a pressure image and a frequency image. For exvery pixel, it gets the pressure and frequency and uses those as an index to get the desired color for that pixel, which it assigns to a new RGB image.