How to control the file size of "capture frame"?

[meegosh]

hi,
i have bs player pro and really like it.
i go to "capture frame" under "options" with no problem, and it saves the frame.
my problem is, the saved frames vary in size a lot, sometimes even when playing from the same video file, the size of the capture differs.
what i want to be able to do is capture "what you see", the full screen image so that when i view it in windows picture and fax viewer it fills up the whole screen rather than going back to a smaller resolution.
when i use "shift+P" it doesn't change what is captured.
i just want to be able to uniformly capture everything so that it is the same file size, and fills the screen, like wallpaper size.
thank you,
meegosh