How to filter out NaNs on images ?

Question

V.D-C 2020-2-10

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/504686-how-to-filter-out-nans-on-images

评论： V.D-C 2020-2-11

Hello everybody,

I would like to create a map where I can assign a brownish color to the areas inside the black contour lines (land). But, I also want to display another layer (the colored one on the figure below) on top of it. The issue is that this additionnal layer has NaNs covering the land and the sea, making all the background look blue.

How can I differentiate the colour of the sea and the land, while having this additionnal layer we see below ?

I thought of one way: I could make all the NaNs from this layer be transparent, so the background land would reappeare. But I don't know how to do that.

Maybe there is another solution but I can't think of any.

Thank you !

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Subhadeep Koley 2020-2-10

Can you provide your matrix / images / maps so that we can reproduce the issue?

V.D-C 2020-2-11

在 MATLAB Online 中打开

Here you have the files (I coudn't put the black contour line but this is not really important).

To display things, I was writing:

imagesc(lat,long,Background);
axis xy;
hold on; 
imagesc(lat,long,overlay_map);

And this overlay has NaNs for every value displayed in blue. I would like to make them transparent so we can see the background on the land parts.

Sorry I did not answer sooner btw, I left work.

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Answer 1

Subhadeep Koley 2020-2-11

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/504686-how-to-filter-out-nans-on-images#answer_414943

在 MATLAB Online 中打开

See if the below code works

clc; close all;
% Load data
load Background.mat
load lat.mat
load long.mat
load overlay_map.mat
% Plot the background image
ax1 = axes;
imagesc(ax1, lat, long, Background);
axis xy; hold on; 
% Plot the foreground image
ax2 = axes;
imAlpha = ones(size(mean_map));
imAlpha(isnan(mean_map)) = 0;
imagesc(ax2, lat, long, mean_map, 'AlphaData', imAlpha);
set([ax1, ax2], 'Position', [0.17 0.11 0.7 .815]);
colorbar(ax2, 'Position', [0.9 0.11 0.025 0.815]);
axis xy; ax2.Visible = 'off'; hold off;