Digital SLR Camera Basics
Images can be recorded in any of the following three sizes: large (L), medium (M), and small (S). The large size for the D5100, for example, is equivalent to about 16 megapixels, the medium size to about 9 mega-pixels, and the small size to about 4 megapixels. Printed on a typical inkjet printer with a resolution of around 300 dpi, the images are about 42 × 28, 31 × 21, and 21 × 14 cm, respectively. While images need not be taken at a large size if they are destined for use as 4 by 6 (10 × 15 cm) prints, the large size is recommended if the images will later be trimmed or enlarged.
The illustration above shows images of different sizes printed at the same resolution. Large images are about four times the size of small images. The differences in the amounts of information each type of image contains can be ascertained by displaying medium and small photos at the same size as large images on a computer monitor.
More details are visible in the large image than in the small image.