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Large format refers to any imaging format of 4×5 inches (102×127 mm) or larger. Large format is larger than "medium format", the 6×6 cm (2¼×2¼ inch) or 6×9 cm (2¼×3½ inch) size of Hasselblad, Rollei, Kowa, and Pentax cameras (using 120- and 220-roll film), and much larger than the 24×36 mm (~ 1.0x1.5 inch) frame of 35 mm format. The main advantage of large format, film or digital, is higher resolution at the same pixel pitch, or same resolution with more larger pixels or grain. A 4×5 inch image has about 16 times the area, and thus 16× the total resolution, of a 35 mm frame.
Large format cameras were some of the earliest photographic devices, and before enlargers were common, it was normal to just make 1:1 contact prints from a 4×5, 5×7, or 8×10-inch negative.