The print function doesn’t know anything about the display device. When you print you have to pass a device independent bitmap. When you zoom in on an image, you can get the scaling factor of the zoomed in image. When you print, you can pass the scaling factor to the print routine. The printed image will be the same as the zoomed in image. There is also another factor to consider – the display device resolution is 96 or 120 dpi. Most printer resolution is 600 dpi. The dpi is a major scaling factor of the image.