Method of optical density correction

Claim 1

A method of correcting measured optical density in which a reflection density of a subject is calculated by measuring reflected light from the subject illuminated by a lamp, comprising the steps of positioning the lamp to illuminate high and low density standard optical density members; measuring the optical density of said high and low standard optical density members using light from said lamp reflected by said density members to obtain measured values of standard high and low optical densities; obtaining data for zero point correction based on the differences between said measured value and preset standard values of densities of said high and low standard optical density members; storing said zero point correction data in a memory; positioning said zero point correction data in a memory; positioning the lamp to illuminate a said subject; measuring the optical density of said subject using light from said lamp reflected by said subject; and correcting the thus-measured value of optical density of said subject by using said zero point correction data read out from said memory, to produce a corrected measured value R, according to the equation R=R.sub.D -α·R.sub.D -K wherein α is a coefficient equal to ##EQU2## R L is said preset value of low standard density, R H is said preset value of high standard density, R 1 is said measured value of low standard density, R 2 is said measured value of high standard density, K is a constant, and R D is said measured value prior to correction; and displaying the measured optical density thus corrected.

Claim 2

A method of correcting measured optical density in which a reflection density of a subject is calculated by measuring reflected light from the subject illuminated by a lamp, comprising the steps of positioning the lamp to illuminate high and low density standard optical density members; measuring the optical density of said high and low standard optical density members using light from said lamp reflected by said density members to obtain measured values of standard high and low optical densities; obtaining data for zero point correction based on the differences between said measured value and preset standard values of densities of said high and low standard optical density members; storing said zero point correction data in a memory; positioning said zero point correction data in a memory; positioning the lamp to illuminate a said subject; measuring the optical density of said subject using light from said lamp reflected by said subject; and correcting the thus-measured value of optical density of said subject by using said zero point correction data read out from said memory, to produce a corrected measured value R, according to the equation R=R.sub.D -α·R.sub.D -K wherein α is a coefficient equal to ##EQU2## R L is said preset value of low standard density, R H is said preset value of high standard density, R 1 is said measured value of low standard density, R 2 is said measured value of high standard density, K is a constant, and R D is said measured value prior to correction; and displaying the measured optical density thus corrected.