How do I specify the output sizes of JPEG, PNG, and TIFF images when using the PRINT function in MATLAB?

I would like to know why the outputs are very large by default.

Answer 1

[MathWorks Support Team]

The JPEG, PNG, and TIFF drivers in MATLAB 5.x and later rely upon a figure's "PaperPosition" to specify the size of the output file. In addition, since the drivers take a snapshot of the figure in order to generate the image, the resolution of the output is dependent on the "-r" specified when printing. For instance, if my figure's PaperPosition is set to the default for most computers:

[.25 2.5 8 6] (in inches) 8 is the width while 6 is the height.

The default -r value (resolution) is 150 dpi. Therefore "print -djpeg filename" will produce a:

8*150 X 6*150 = 1200 X 900 pixel image

There are two easy ways to make images the size you want (these examples are written for the JPEG driver but the TIFF driver can be substituted):

1) Specify the PaperPosition and resolution to get the desired output size.

For instance, if you want your figure to be of dimensions 400 X 300 pixels in the output file then execute the following code:

plot(1:10) % Example graph

set(gcf,'PaperUnits','inches','PaperPosition',[0 0 4 3])

print -djpeg filename.jpg -r100

The resulting JPEG file will have dimensions 4*100 X 3*100 or 400 X 300.

2) Make the output file the same size as the figure on the screen.

This is a little more involved than #1 but the results are consistent with what you see on the screen. The code to do this is included below. Save it as screen2jpeg.m:

function screen2jpeg(filename)

%SCREEN2JPEG Generate a JPEG file of the current figure with

%   dimensions consistent with the figure's screen dimensions.

%

%   SCREEN2JPEG('filename') saves the current figure to the

%   JPEG file "filename".

%

%    Sean P. McCarthy

%    Copyright (c) 1984-98 by MathWorks, Inc. All Rights Reserved

if nargin < 1

     error('Not enough input arguments!')

end

oldscreenunits = get(gcf,'Units');

oldpaperunits = get(gcf,'PaperUnits');

oldpaperpos = get(gcf,'PaperPosition');

set(gcf,'Units','pixels');

scrpos = get(gcf,'Position');

newpos = scrpos/100;

set(gcf,'PaperUnits','inches',...

     'PaperPosition',newpos)

print('-djpeg', filename, '-r100');

drawnow

set(gcf,'Units',oldscreenunits,...

     'PaperUnits',oldpaperunits,...

     'PaperPosition',oldpaperpos)

Note that for improved image quality, you can create a SCREEN2PNG function based on the code above and change the PRINT command to use the '-dpng' argument instead of the '-djpeg' argument.

Please note that this program is provided "as is" without further support.