1. A printed sheet measurement apparatus for acquiring image data by capturing an image on a printed sheet sampled from a printing apparatus to compute a colorimetric value on said printed sheet based said image data for ink control in said printing apparatus, said printed sheet measurement apparatus comprising: a storing element for storing first image data obtained by capturing the image on said printed sheet, and second image data obtained based on reference image data related to an image on a reference printed sheet; a display element for displaying said first image data and said second image data; a specifying element for specifying a pair of corresponding points for each of said first and second image data displayed on said display element; a coordinate computing element for associating said first and second image data with each other based on said corresponding points to compute a pair of coordinates of a first objective point for one of said first and second image data corresponding to a pair of coordinates of a second objective point for the other of said first and second image data; and a colorimetric value computing element for computing a calorimetric value at each of said first and second objective points corresponding to each other, based on pixel values at said first and second objective points for said first and second image data.