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Matthias Pospiech > Programming > matlab > pcolor plots with publication ready formating

pcolor plots with publication ready formating

Matlab has many possibilities to create plots even fancy ones. However its defaults are very seldom suitable to use the plots directly for a publication. The following minimal code demonstrates how to generate a pcolor plot for 2D data with x- and y-axis. The data was calculated using the function shown here.

pcolor(xAxis, yAxis, Data2D); 
shading flat; % do not interpolate pixels
colorbar % add colorbar
 
xlabel('x / µm');
ylabel('y / µm');
pcolor-example-simple

This however is not optimal. Font and fontsizes are not optimal, the color depth should be higher and tics are not shown anymore. Furthermore the colorbar should have an label as well.

The following code demonstrates a general approach how to solve all these problems and achieve directly a plot output which can be used directly for publications. The followin picture shows the resulting image:

pcolor-example

First the environment is set up (not necessary if you just want to plot) and variables for plotting are defined.

% clear command window, figures and all variables
clc; clf; clear all; 
 
%% Common variables
FontSize = 12;
FontName = 'MyriadPro-Regular'; % or choose any other font
 
doExportPlot = true;
languageEnglish = false;

Next, the data for plotting is created. Here a previous shown example is used

%% Calculation
% calculate in single line (fastest method)
xMat = (xAxis' * ones([1 yPoints]))';
yMat = yAxis' * ones([1 xPoints]);
Data2D = Ripple(xMat, yMat);
 
Data2D = Data2D - min(min(Data2D)); % normalize to 0-1
Data2D = Data2D / max(max(Data2D));

Then the plot window is opened and configured. Here a fixed size in cm is used. The z-buffer is used because opengl has rounding errors and should therefore be avoided if not necessary. Furthermore the position of the plot within the window is configured.

%% start plot
 
% figure dimensions in cm. I choose 1.5 or 2 times 
% the target size typically. If figure is display in
% document much smaller increase the fontsize.
 
figure_width = 14;  
figure_height = 10;
 
% --- setup plot windows
figuresVisible = 'on'; % 'off' for non displayed plots (will still be exported)
hfig = figure(1); clf;
    set(hfig,'Visible', figuresVisible)
 
    set(hfig, 'units', 'centimeters', 'pos', [5 5 figure_width figure_height])   
    set(hfig, 'PaperPositionMode', 'auto');    
    set(hfig, 'Renderer','Zbuffer'); 
    set(hfig, 'Color', [1 1 1]); % Sets figure background
    set(gca, 'Color', [1 1 1]); % Sets axes background
 
% --- dimensions and position of plot 
hsp = subplot(1,1,1, 'Parent', hfig);
set(hsp,'Position',[0.15 0.17 0.75 0.80]);

The actual plot is still a few lines:

%% plot
colorDepth = 1000;
colormap(jet(colorDepth));
pcolor(xAxis, yAxis, Data2D);

Now the plot needs to be configured. First the pcolor must not have black lines between each data point (the plot would be black). This is achieved by setting the shading. In case of flat not interpolation is done. This might look nicer, but in case of scientific data is close to cheating. The axis properties are important, because matlab does not care itself about scaling. This means that the x- and y-axis might be square although the axis values have a factor of 1:10. The image ratio is set to the axis ratio by the property ‚image‘. Additionally several properties for the figure can be set. Most important are the TickLength and the LineWidth.

%%  setup axis plot properties
% shading interp; % interpolate pixels
shading flat; % do not interpolate pixels
axis on;      % display axis
axis tight;   % no white borders
axis image;   % real x,y scaling
 
set(gca, ...
    'CLim' , [0 1], ...
    'Box'         , 'on'      , ...
    'TickDir'     , 'in'      , ...
    'TickLength'  , [.015 .015] , ...
    'XMinorTick'  , 'off'      , ...
    'YMinorTick'  , 'off'     , ...
    'XGrid'       , 'off'     , ...
    'YGrid'       , 'off'     , ...
    'XColor'      , [.0 .0 .0], ...
    'YColor'      , [.0 .0 .0], ...
    'LineWidth'   , 0.6        );

optionally the axis ticks can be configured

%% axis ticks
set(gca,'XTick',-15:5:15)
set(gca,'YTick',-10:5:10)

Next the axis labels are set up. Here I define them in both german end english. That has the advantage, that I can create the figure easily in both languages. The labels are all set with saving of handles, to be able to configure them later.

%% label texts
TITLE = '';
if (languageEnglish)
    xLabelText = 'x / µm';  
    yLabelText = 'y / µm';
    zLabelText = 'normalized intensity';
else
    xLabelText = 'x / µm';
    yLabelText = 'y / µm';
    zLabelText = 'normierte Intensität';
end
 
% save handles to set up label properties
hTitle = title(TITLE);
hXLabel = xlabel(xLabelText);
hYLabel = ylabel(yLabelText);

The colorbar is still missing. Here a label and ticks are defined, and the TickLength and LineWidth is configured.

%% colorbar
caxis([0 1]);
hcb = colorbar('location','EastOutside');
hcLabel = ylabel(hcb,zLabelText);
set(hcb,'YTickLabel',0:0.2:1, 'Ytick', 0:0.2:1)
set(hcb,'YTickMode','manual')
set(hcb, ...
  'Box'         , 'on'     , ...
  'TickDir'     , 'in'     , ...
  'TickLength'  , [.015 .015] , ...
  'LineWidth'   , 0.6);

Last all handles need to be configured. Basically that means setting up the fonts for all.

%% set properties for all handles
set([gca, hcb, hTitle, hXLabel, hYLabel, hcLabel], ...
    'FontSize'   , FontSize    , ...
    'FontName'   , FontName);

And finally some bugs need to be fixed. fixLabels changes the decimal point character to ‚,‘ (see below) and the last line brings the tics to the top again, which are overwritten by matlab.

%% last 'bug' fixes
 
% change decimal point to ',' for german text
if (~languageEnglish)
     fixLabels(gca);
     fixLabels(hcb);
end
% bring axis on top again (fix matlab bug)
set(gca,'Layer', 'top');
fixLabels (not optimal, be nevertheless working):
function fixLabels( axis )
 
xlabels = get(axis, 'XTickLabel');
for k=1:size(xlabels,1)
    xlabels(k,:) = strrep(xlabels(k,:), '.', ',');
end
set(axis, 'XTickLabel', xlabels);
 
ylabels = get(axis, 'YTickLabel');
for k=1:size(ylabels,1)
    ylabels(k,:) = strrep(ylabels(k,:), '.', ',');
end
set(axis, 'YTickLabel', ylabels);
 
set(axis, 'XTickMode', 'manual');
set(axis, 'YTickMode', 'manual');
 
end

In the end we might want to export the plot. Here the printing is done to a png file with a resolution of 400 dpi. Since matlab is not filling the plot window and large white borders might surround the actual plot, the png file is cropped using the crop function by Andrew Bliss.

%% export
drawnow
 
SaveDir = '';
SaveName = 'pcolor-example';
 
if (doExportPlot)
    IMAGENAME = [SaveDir SaveName]; 
    print(hfig, ['-r' num2str(400)], [IMAGENAME '.png' ], ['-d' 'png']);    
    crop([IMAGENAME '.png']);
    display('finished plot export')
end
 
% close(hfig);
Download the complete file:   PcolorExample.m (4,1 KiB)

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