How to plot x,y, and intensity with NaN values present in the intensity data?

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Alexandria Will-Cole 2017-9-25

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https://ww2.mathworks.cn/matlabcentral/answers/358299-how-to-plot-x-y-and-intensity-with-nan-values-present-in-the-intensity-data

评论： Walter Roberson 2017-9-26

Here is my code for my attempt to plot x, y, and intensity (referred to as v) on a color plot. I keep running into an issue where I cannot find the maximum of intensity due to NaN's present. Any advice to mitigate this issue or help refining this code is welcome. Thanks!

%plotting script
% Make an image of the points, then apply a colormap
x = x(:); % Extract x value
y = y(:); % Extract y value
v = v(:); % Extract intensity value
%find max and min values
minX = min(x,[],1);
maxX = max(x,[],1);
minY = min(y,[],1);
maxY = max(y,[],1);
[minV,~] = nanmin(v); 
[maxV,~] = nanmax(v);
% Make image be 500 by 700
rows = 500;
columns = 700;
grayImage = zeros(rows, columns, 'uint8');
for k = 1 : length(x)
    row = ceil((y(k) - minY) * rows / (maxY - minY));
    column = ceil((x(k) - minX) * columns / (maxX - minX));
  if (row == 0)
    row = 1;
  end
  if (column == 0)
    column = 1;
  end
  grayImage(row, column) = uint8(255 * (v(k) - minV) / (maxV - minV));
end
imshow(grayImage);
colorbar;
% Colormap is not gray scale.
% Apply some other colormap if you want
colormap(jet(256));

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Walter Roberson 2017-9-25

You appear to me to be properly using nanmin() and nanmax().

The only thing I see is that you have been a little lax about handling v(k) being nan. Your calculation will result in uint8(nan) which turns out to be 0. If that is the result you want then I recommend adding a comment about that.

Also, the calculations (maxY - minY) and (maxV - minV) can be done ahead of time and stored in variables instead of being done every iteration. Also watch out for the possibility of constant input, in which case (maxV - minV) would be 0.

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Answer 1

Image Analyst 2017-9-25

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/358299-how-to-plot-x-y-and-intensity-with-nan-values-present-in-the-intensity-data#answer_283108

编辑：Image Analyst 2017-9-25

在 MATLAB Online 中打开

I don't see any plotting going on. Anyway, to extract only non-NaN values from an array, such as grayImage or v or whatever, do this:

goodValues = v(~isnan(v));

Then you can get the max, min, mean, etc. of those good values.

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Alexandria Will-Cole 2017-9-25

编辑：Walter Roberson 2017-9-26

在 MATLAB Online 中打开

I am able to find the maximum and I actually want the minimum restricted to 0, so this is what I have now, but now I am getting an error saying that the "Index exceeds matrix dimensions." Thoughts?

Thanks,

% Make an image of the points, then apply a colormap
x = x(:); % Extract x value
y = y(:); % Extract y value
v=v(:);
%find max and min values
minX = min(x,[],1);
maxX = max(x,[],1);
minY = min(y,[],1);
maxY = max(y,[],1);
%dealing with NaN
v(isnan(v)) = 0; %set all NaN to zero
minV=0;
maxV=max(v,[],1);
% Make image be 500 by 700
rows = 500;
columns = 700;
grayImage = zeros(rows, columns, 'uint8');
for k = 1 : length(x)
    row = ceil((y(k) - minY) * rows / (maxY - minY));
    column = ceil((x(k) - minX) * columns / (maxX - minX));
  if (row == 0)
    row = 1;
  end
  if (column == 0)
    column = 1;
  end
  grayImage(row, column) = uint8(255 * (v(k) - minV) / (maxV - minV));
end
imshow(grayImage);
colorbar;
% Colormap is not gray scale.
% Apply some other colormap if you want
colormap(jet(256));

Image Analyst 2017-9-25

编辑：Image Analyst 2017-9-25

We don't have your v so can't even run your code. So I quit at that point. Can you attach v in a .mat file, so we can try to help you?

Also, read this: http://www.mathworks.com/matlabcentral/answers/13205#answer_18099

Walter Roberson 2017-9-26

在 MATLAB Online 中打开

In my test, I do not get index out of range.

Note: to get your color right, you should do

cmap = jet(256);
imshow(grayImage, cmap);
colorbar();

without calling colormap() after that.

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