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set NaN as another color than default using imagesc

216 visualizaciones (últimos 30 días)
Gaëlle
Gaëlle el 12 de Jul. de 2013
Comentada: Walter Roberson el 17 de Nov. de 2023
Hello, I have a matrix filled probability numbers (i.e. ranging from 0 to 1) or NaN when the probability is not computed. I would like to display this matrix as a color table (e.g. using imagesc), in order to have a quick visualisation of the result. The colorbar range is thus set as 0 to 1 since I am interested in probability values. However, I would like the NaN fields to appear with another color than the default "-inf" (here the color of 0 since the down limit for the color is set for value 0), for example gray. How can I do this? Thank you very much, Gaelle

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Kelly Kearney
Kelly Kearney el 12 de Jul. de 2013
Editada: Kelly Kearney el 12 de Jul. de 2013
Do you need to use imagesc, or are you open to using pcolor? The latter will leave NaNs blank, so they will appear the same color as the axis background.
Example:
data = rand(10);
data(data > 0.9) = NaN;
[nr,nc] = size(data);
subplot(2,1,1);
imagesc(data);
subplot(2,1,2);
pcolor([data nan(nr,1); nan(1,nc+1)]);
shading flat;
set(gca, 'ydir', 'reverse');
(The NaN-padding in the pcolor call is so the last row and column are shown, similar to imagesc)
  3 comentarios
Kelly Kearney
Kelly Kearney el 20 de En. de 2017
Just set the 'clim' property of the axes:
data = rand(10);
data(data > 0.9) = NaN;
[nr,nc] = size(data);
ax(1) = subplot(2,1,1);
imagesc(data);
ax(2) = subplot(2,1,2);
pcolor([data nan(nr,1); nan(1,nc+1)]);
shading flat;
set(gca, 'ydir', 'reverse');
set(ax, 'clim', [0 1]);
SeanC
SeanC el 20 de En. de 2017
Thanks!

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Más respuestas (5)

Charles Krzysik
Charles Krzysik el 27 de Abr. de 2017
If you want to use imagesc rather than pcolor, you can set the AlphaData property to zero everywhere you have a NaN. This will show the background wherever there is no data; you can then additionally set the background colour, if you so choose. In this example I'm setting it to black:
imAlpha=ones(size(Data_Array));
imAlpha(isnan(Data_Array))=0;
imagesc(Data_Array,'AlphaData',imAlpha);
set(gca,'color',0*[1 1 1]);
  4 comentarios
TheStranger
TheStranger el 2 de Jun. de 2021
Editada: TheStranger el 2 de Jun. de 2021
This is the most useful comment of this thread, yet not with the most votes!
Maria Cristina Araya Rodriguez
Maria Cristina Araya Rodriguez el 17 de Nov. de 2023
I agree, many thanks, in fact this is a good solution when using a ".cpt" colour scale.

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Lauren
Lauren el 7 de Nov. de 2017
imagesc(data,'AlphaData',~isnan(data))
  8 comentarios
Walter Roberson
Walter Roberson el 17 de Nov. de 2023
If you have RGB data, some elements of which might be NaN, then
%with sufficiently new versions of MATLAB
scaled_data = rescale(YourRGBData, 0, 1);
alpha_data = 0 + ~any(isnan(YourRGBData), 3);
image(scaled_data, 'AlphaData', alpha_data);
%older versions of MATLAB
scaled_data = mat2gray(YourRGBData);
alpha_data = 0 + ~any(isnan(YourRGBData), 3);
image(scaled_data, 'AlphaData', alpha_data);
In practice if your RGB data is single or double precision data that uses only integral values 0 to 255, but also has some NaN, then you would probably use slightly different code,
scaled_data = uint8(YourRGBData);
alpha_data = 0 + ~any(isnan(YourRGBData), 3);
image(scaled_data, 'AlphaData', alpha_data);

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Evan
Evan el 12 de Jul. de 2013
Editada: Evan el 12 de Jul. de 2013
You can use the isnan function to find the indices of all NaNs, then set those elements to another value:
Example:
>>A = [4 NaN 3;NaN 2 1];
>>A(isnan(A)) = 255
A =
4 255 3
255 2 1
  6 comentarios
Gaëlle
Gaëlle el 12 de Jul. de 2013
Movida: DGM el 25 de Mzo. de 2023
But one thing which is bad using your way: the colorbar scale is not set according to the values of the probabilities. So actually, I cannot use your trick...
Adil Masood
Adil Masood el 10 de Dic. de 2015
Movida: DGM el 25 de Mzo. de 2023
Thanks you for a smart solution. There is just one correction: Instead of
scatter(ii,jj,'ok','MarkerEdgeColor',[1 1 1],'MarkerFaceColor',[0 0 0],'LineWidth',2,'SizeData',100)
it should be
scatter(jj,ii,'ok','MarkerEdgeColor',[1 1 1],'MarkerFaceColor',[0 0 0],'LineWidth',2,'SizeData',100)
Its because imagesc() plots elements of matrix indexed as (row,column), while scatter() handles elements as (x,y).

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Gaëlle
Gaëlle el 12 de Jul. de 2013
Hi, I am open to use pcolor, it just seemed more complicated to use than imagesc. I will try to implement it. Thank you!

Ben
Ben el 4 de Dic. de 2014
Editada: Ben el 10 de Dic. de 2014
If using pcolor, NaNs are set to the axis background color. So you can set your colormap to color non-NaNs, and set the axis background color to set the color for NaNs. For example, to set NaNs black you can use: set(gca,'color','k')
  1 comentario
Walter Roberson
Walter Roberson el 20 de En. de 2017
For pcolor the nan are not exactly set to the axes background color: instead a hole is created that allows whatever is under to be visible. If nothing else is there that would be the axes background, but there could also be a different graphics object there.

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