A method for causing a device to generate a distribution image showing a molar concentration ratio between a first biological substance and a second biological substance included in a biological tissue of which an absorption spectrum within a predetermined wavelength range has a first isosbestic point, a second isosbestic point, a third isosbestic point and a fourth isosbestic point in ascending order of wavelength, the method comprising: a step of acquiring first imaging data G 1 by taking an image of the biological tissue using light extracted from white light using a first optical filter configured to collectively selectively extract light in a first wavelength range demarcated by the first isosbestic point and the second isosbestic point, light in a second wavelength range demarcated by the second isosbestic point and the third isosbestic point, and light in a third wavelength range demarcated by the third isosbestic point and the fourth isosbestic point; a step of acquiring second imaging data G 2 by taking an image of the biological tissue using light extracted from the white light using a second optical filter configured to selectively extract light in the second wavelength range; and a step of generating the distribution image on the basis of the first imaging data G 1 and the second imaging data G 2; wherein the step of generating the distribution image on the basis of the first imaging data G 1 and the second imaging data G 2 further comprises: a step of acquiring an absorbance A 1 of the biological tissue in a transmission wavelength range of the first optical filter on the basis of the first imaging data G 1; a step of acquiring an absorbance A 2 of the biological tissue in a transmission wavelength range of the second optical filter on the basis of the second imaging data G 2; and a step of generating the distribution image on the basis of the absorbance A 1 and the absorbance A 2; wherein the step of generating the distribution image on the basis of the absorbance A 1 and the absorbance A 2 includes: a step of calculating an index X using Expression 5; and X = A 1 − 2 k A 2 where k is a constant a step of generating the distribution image on the basis of the index X. a step of acquiring first imaging data G 1 by taking an image of the biological tissue using light extracted from white light using a first optical filter configured to collectively selectively extract light in a first wavelength range demarcated by the first isosbestic point and the second isosbestic point, light in a second wavelength range demarcated by the second isosbestic point and the third isosbestic point, and light in a third wavelength range demarcated by the third isosbestic point and the fourth isosbestic point; a step of acquiring second imaging data G 2 by taking an image of the biological tissue using light extracted from the white light using a second optical filter configured to selectively extract light in the second wavelength range; and a step of generating the distribution image on the basis of the first imaging data G 1 and the second imaging data G 2; wherein the step of generating the distribution image on the basis of the first imaging data G 1 and the second imaging data G 2 further comprises: a step of acquiring an absorbance A 1 of the biological tissue in a transmission wavelength range of the first optical filter on the basis of the first imaging data G 1; a step of acquiring an absorbance A 2 of the biological tissue in a transmission wavelength range of the second optical filter on the basis of the second imaging data G 2; and a step of generating the distribution image on the basis of the absorbance A 1 and the absorbance A 2; a step of acquiring an absorbance A 1 of the biological tissue in a transmission wavelength range of the first optical filter on the basis of the first imaging data G 1; a step of acquiring an absorbance A 2 of the biological tissue in a transmission wavelength range of the second optical filter on the basis of the second imaging data G 2; and a step of generating the distribution image on the basis of the absorbance A 1 and the absorbance A 2; wherein the step of generating the distribution image on the basis of the absorbance A 1 and the absorbance A 2 includes: a step of calculating an index X using Expression 5; and X = A 1 − 2 k A 2 where k is a constant a step of generating the distribution image on the basis of the index X. a step of calculating an index X using Expression 5; and X = A 1 − 2 k A 2 where k is a constant a step of generating the distribution image on the basis of the index X.