2D color map shows the image correct but the Y scale is flipped.
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Sneha Kandapal
el 20 de Oct. de 2023
Comentada: Sneha Kandapal
el 21 de Oct. de 2023
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1516681/image.png)
I wrote a code for plotting 2D color map. Though it works and get the image of what I wnat but the Y scale is flipped. The Y axis is in logarithmic scale and shows the scale from positive to negative instead of negative to positive. I tried multiple ways to flip it but nothing happens. I have also attached an image of how the Y scale should look like.
% Prompt the user to select multiple data files
[dataFiles, dataDirectory] = uigetfile('*.txt', 'Select data files', 'MultiSelect', 'on');
% Check if the user canceled the file selection
if isequal(dataFiles, 0)
disp('No files selected. Exiting...');
return;
end
% Prompt the user to select an output directory
outputDirectory = uigetdir('Select an output directory', 'Specify Output Directory');
% Check if the user canceled the output directory selection
if outputDirectory == 0
disp('No output directory selected. Exiting...');
return;
end
% Initialize variables to store data
xData = [];
yData = [];
% Loop through selected data files
for i = 1:length(dataFiles)
% Construct the full file path
fullFilePath = fullfile(dataDirectory, dataFiles{i});
% Read the data from the current file
data = dlmread(fullFilePath);
% Extract x and y data (1st and 4th columns)
x = data(:, 1);
y = data(:, 4);
% Apply the formula to the y data
y = (10.^((y - 3.51307) / 0.22845)) ./ (7.75E-5 * 0.2);
% Append data to the storage variables
xData = [xData; x];
yData = [yData; y];
end
% Define the number of bins for the histogram
numXBins = 200;
% Adjust as needed
numYBins = 100; % Adjust as needed
% Define the bin edges for the X and Y axes
xBinEdges = linspace(min(xData), max(xData), numXBins);
yBinEdges = logspace(log10(min(yData)), log10(max(yData)), numYBins);
% Create a 2D histogram color map with specific bin edges
h = histcounts2(xData, yData, xBinEdges, yBinEdges);
% Create a color map using imagesc with the Y-axis and scale reversed
figure;
imagesc(xBinEdges, flip(log10(yBinEdges)), log(h)'); % Reverse the Y-axis and its scale
colormap('jet'); % Use the 'jet' colormap for colorful visualization
colorbar; % Display the color bar for the Z-axis (point density)
% Customize the plot appearance
xlabel('X-Axis (Column 1)');
ylabel('Log(Y-Axis)'); % Y-axis is logarithmic and reversed
title('2D Histogram Color Map of Multiple Data Files');
% Specify the output image file path
outputImageFilePath = fullfile(outputDirectory, 'histogram_colormap.png');
% Save the color map plot as an image (e.g., PNG)
saveas(gcf, outputImageFilePath, 'png');
% Display the path where the image is saved
disp(['2D Histogram Color Map saved to: ' outputImageFilePath]);
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1516676/image.jpeg)
Editor's note: reformatted unreadable one-lined code block
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Respuesta aceptada
Dyuman Joshi
el 20 de Oct. de 2023
Editada: Dyuman Joshi
el 20 de Oct. de 2023
Revert it back to normal -
C = [0 2 4 6; 8 10 12 14; 16 18 20 22];
imagesc(C)
set(gca, 'YDir', 'normal')
5 comentarios
DGM
el 21 de Oct. de 2023
You can try either:
% Create a pseudocolor plot using pcolor with reversed Y-axis scale
pcolor(X, Y, imresize(log(h).',size(X)));
shading interp; % Use interpolated shading for smooth color transitions
or
imagesc(imresize(log(h).',size(X)),'xdata',X(:),'ydata',Y(:));
set(gca,'ydir','normal')
pcolor() will render NaNs differently than imagesc() does.
Más respuestas (2)
Sulaymon Eshkabilov
el 20 de Oct. de 2023
Use 'reverse' option for the plot axis value direction, e.g.:
t=linspace(0,1.2, 1e3);
dt = t(2)-t(1);
Fs = 1/dt;
f1 = 5;
f2 = 25;
f3 = 100;
Z = sin(2*pi*t*f1)+0.75*sin(2*pi*t*f2)+0.5*cos(2*pi*t*f3)+0.25*randn(size(t));
[P,ff,tt] = pspectrum(Z,Fs,'spectrogram');
figure(1)
waterfall(ff,tt,P')
xlabel('Frequency (Hz)')
ylabel('Time (seconds)')
FIG = gca;
% X and Y axis values are in the reverse order
FIG.XDir = 'reverse'; % This reverses the values of x axis
FIG.YDir = 'reverse'; % This reverses the values of y axis
view([30 45])
% Compare to this one: all axis values are in default order given by MATLAB
% plot tools/fcns
figure(2)
waterfall(ff,tt,P')
xlabel('Frequency (Hz)')
ylabel('Time (seconds)')
view([30 45])
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