Ahhh, gotcha... my monitor is set to 1600x1200, and before I open a film file in the Viewer, I maximize the Viewer window, filling the screen.
After PrintScreening and pasting into PhotoShop, I crop at a consistent size of 1200x900. Never resize an image larger than it's original size.
Another trick... although you may not want it IN the game, you can turn on AntiAliasing for the Film Viewer; it makes the shots look even nicer