An image reading system with a light irradiating portion for irradiating light onto a predetermined range of the surface of a manuscript to be read, an image reading portion for outputting a signal obtained by first converting light reflected or transmitted by the manuscript into a luminance signal and then referring to a look-up table, an interface portion for inputting a signal from and outputting a signal to an external computing device, a manuscript scanning portion for scanning the surface of the manuscript, a central processing portion for controlling the manuscript scanning portion and a storage portion capable of storing at least one kind of density transformation curve data.