How to use strcat in imwrite to save multiple figures

I am trying to save figures in a loop using strcat and imwrite but I get the following error:

Error using imwrite (line 442)

Expected DATA to be one of these types:

double, single, uint8, uint16, uint32, uint64, int8, int16, int32, int64,

logical

Instead its type was matlab.graphics.chart.primitive.Line.

This is a subset of the code I am using to make the figures:

nfile = 'filename.nc';
z = [];
T = [];
L = [];

for j = 5:60;
    nfile = strcat('folder_location/40f17_',num2str(j,'%02d'),'_1.nc');
    z  = ncread(nfile, 'z');
    T  = ncread(nfile, 'T');
    L  = ncread(nfile, 'L');
    
    MeansL = mean(L,'omitnan');
    MeansT = mean(T,'omitnan');
    MeansZ = mean(z,'omitnan');
    
    n_L = length(MeansL);
    n_T = length(MeansT);
    n_z = length(MeansZ);
    time_L = 1:n_L;
    time_T = 1:n_T;
    time_z = 1:n_z;
    
    plotL = plot(time_L,MeansL);
    imwrite(plotL,strcat('folder_location/L40f17_',num2str(j,'%02d'),'.png'));
    
    plotT = plot(time_T,MeansT);
    imwrite(plotT,strcat('folder_location/T40f17_',num2str(j,'%02d'),'.png'));
    
    plotZ = plot(time_z,MeansZ);
    imwrite(plotZ,strcat('folder_location/z40f17_',num2str(j,'%02d'),'.png'));
end

It's just simple line graphs that I am trying to save directly as png files.

Answer 1

[Walter Roberson]

See exportgraphics()

[Kelsey Ward]

That gave me "Specified handle is not valid for export" error.

[Walter Roberson]

Are we to understand that you want to just the colored line (and any associated markers) -- without any title or labels or tickmarks or grid lines?

Most people want to save the axes rather than the single line.

[Kelsey Ward]

How do I save the entire plot instead?

[DGM]

You might be taking my earlier advice a little too severely. My point was to discourage using figure capture when your inputs are strictly raster images. When you're trying to capture graphics objects (line plots, charts, etc), it's appropriate to use exportgraphics(), saveas(), etc.

exportgraphics(gca,'myfilename.png') % just the axes 

or

exportgraphics(gcf,'myfilename.png') % the figure

[Walter Roberson]

nfile = 'filename.nc';
z = [];
T = [];
L = [];

ax = gca;

for j = 5:60;
    nfile = strcat('folder_location/40f17_',num2str(j,'%02d'),'_1.nc');
    z  = ncread(nfile, 'z');
    T  = ncread(nfile, 'T');
    L  = ncread(nfile, 'L');
    
    MeansL = mean(L,'omitnan');
    MeansT = mean(T,'omitnan');
    MeansZ = mean(z,'omitnan');
    
    n_L = length(MeansL);
    n_T = length(MeansT);
    n_z = length(MeansZ);
    time_L = 1:n_L;
    time_T = 1:n_T;
    time_z = 1:n_z;
    
    plot(ax, time_L,MeansL);
    exportgraphics(ax,strcat('folder_location/L40f17_',num2str(j,'%02d'),'.png'));
    
    plot(ax, time_T,MeansT);
    exportgraphics(ax, plotT,strcat('folder_location/T40f17_',num2str(j,'%02d'),'.png'));
    
    plot(ax, time_z,MeansZ);
    exportgraphics(ax, plotZ,strcat('folder_location/z40f17_',num2str(j,'%02d'),'.png'));
end