Patent ID: 9536162
Date: 2017-01-03
CPC Classifications: A63F,G06K

Claim:
1. A method of detecting an invisible mark in a card, comprising: (a) a normalization step for calculating first normal light, second normal light, and third normal light by normalizing first light, second light, and third light that form respective pixels in an extraction image of the card; (b) a chrominance calculation step for obtaining first chrominance light, second chrominance light, and third chrominance light by calculating a difference in a color tone between two pieces of normal light not overlapping with each other, from among the first normal light, the second normal light, and the third normal light normalized in the step (a); and (c) an image acquisition step for calculating histograms of the first chrominance light, the second chrominance light, and the third chrominance light calculated in the step (b) and obtaining a detection image of the card by stretching the histograms so that first distribution light, second distribution light, and third distribution light forming one pixel are calculated, wherein the normalization step comprises steps of: calculating a dark and shade value Gray calculating an average dark and shade value Gray calculating first average light, second average light, and third average light by applying the average dark and shade value Gray calculating the first normal light, the second normal light, and the third normal light by stretching histograms of two different average lights, from among the first average light, the second average light, and the third average light, based on a histogram of a remaining one average light, from among the first average light, the second average light, and the third average light, that is different from the two different average lights, further wherein each of the dark and shade values Gray (wherein R (x,y) is the first light forming a specific pixel, G (x,y) is the second light forming the specific pixel, B (x,y) is the third light forming the specific pixel, and (x, y) is coordinates of the specific pixel), the first average light, the second average light, and the third average light are calculated by respectively (wherein R′ (x,y) is the first average light in which the average dark and shade value Gray (x,y) has been applied to the first light, G′ (x,y) is the second average light in which the average dark and shade value Gray (x,y) has been applied to the second light, and B′ (x,y) is the third average light in which the average dark and shade value Gray (x,y) has been applied to the third light), and the first normal light, the second normal light, and the third normal light are calculated by and G″ (x,y) , respectively (wherein R″ (x,y) is the first normal light that is histogram-stretched from the first average light based on the histogram of the second average light, B″ (x,y) is the third normal light that is histogram-stretched from the third average light based on the histogram of the second average light, G″ (x,y) is the second normal light and is identical with the second average light, G′ (min) is a minimum value of the second average light, and G′ (max) is a maximum value of the second average light).