Plot in matlab with imagesc with different range colors in colorbar/colormap

Hello to everybody.

I am trying to have an image plot with imagesc with different range colors. I explain myself.

The code is the following:

load Corr_matrix_IMS_All_Riordinato_Uncorrelated.txt
imagesc(Corr_matrix_IMS_All_Riordinato_Uncorrelated)
colormap(gray(4))
colorbar
caxis([-0.55 1]);

I enclose here the figure i obtain.

I need 4 colours in gray scale with the following limits [-0.55 0], [0 0.5], [0.5 0.9], [0.9 1]. Matlab makes 4 colours but just divides equally the colours range, like the picture enclosed.

I googled a lot but it was not really helpful.

I hope somebody can handle this.

Thank you very much in advance.

Best regards,

Alban Kita

Answer 1

[Walter Roberson]

You need to create a color map as follows:

rows 1 to 11:    0   0   0
rows 12 to 21: 1/3 1/3 1/3
rows 22 to 29: 2/3 2/3 2/3
rows 30 to 31: 1     1   1

Each row covers a span of 0.05 in original value. So row 1 covers -.55 to -.50, row 2 covers -0.50 to -.45, row 3 covers -0.45 to -0.40, and so on. But it is okay that those are separate slots in the colormap, because they are assigned the same color.

You will also need to imagesc(YourArray, [-0.55 1])

just in case the array has slightly different contents that does not exactly match the boundaries you set out.

Answer 2

[Alban Kita]

Thank you very much Walter Roberson.

It worked perfectly.

Best regards

Alban Kita