通常默认情况下，print命令输出图像为 8*5inches，无视屏幕显示尺寸
通过命令行修改的话有三步

1 设置paperposition为manual
set(gcf,'PaperPositionMode', 'manual')
[ auto | {manual} ]

2 设置paperunit  
set(gcf,'PaperUnits','inches')
[ {inches} | centimeters | normalized | points ]

3 设置paperposition
set(gcf,'PaperPosition',[left,bottom,width,height])

例如
set(gcf, 'PaperPositionMode', 'manual');
set(gcf, 'PaperUnits', 'points');
set(gcf, 'PaperPosition', [0 0 640 480]);

还有一个相关命令是papersize
paperposition 是placement，代表图像在paper中的所处位置。left和bottom计算好，就可以使图像在paper中居中
papersize是纸张大小;position要比size小的

PaperPosition
    four-element rect vector
    Location on printed page. A rectangle that determines the location of the figure on the printed page. Specify this rectangle with a vector of the form
     rect = [left, bottom, width, height]
    where left specifies the distance from the left side of the paper to the left side of the rectangle and bottom specifies the distance from the bottom of the page to the bottom of the rectangle. Together these distances define the lower-left corner of the rectangle. width and height define the dimensions of the rectangle. The PaperUnits property specifies the units used to define this rectangle.

要使图像比例输出与屏幕显示的一致，可以使用如下命令
屏幕显示图像尺寸可以plot时用 set(gcf,'position',[left bottom width height]) 调整，或者print之前拖动窗口手动调整

This example exports a figure at screen size to a 24-bit TIFF file, myfigure.tif.

% set(gcf,'position',[80 100 800 600])  % 如果手动拖放，则不需要这一行命令
set(gcf, 'PaperPositionMode', 'auto')   % Use screen size
print -dtiff myfigure