在网上发现如下codes，可以生成透明图形。

% If you ever wondered how to get a matlab figure transparent (particularly usefull when you export it to formats that feature transparency, like eps, gif, png, etc.), here is how you do it:

% you created a figure and it is "current". % the following, you could have guessed
set(gcf,\'color\',\'none\');
set(gca,\'color\',\'none\');
% but this following little detail took me ages to figure out
set(gcf,\'InvertHardCopy\',\'off\');

打开一个.fig的文件，在command中运行上面三行命令 Edit－>Copy Figure－>在powerpoint中粘贴，就得到背景透明的图片。