A Way of Converting Color Images to Gray Scale Ones for the Color Blinds -Reducing the Colors for Tokyo Subway Map-

Abstract

THIS paper proposes a way of removing noises and reducing the number of colors contained in a JPEG image. Main purpose of this project is to convert color images to monochrome images for the color blinds. We treat the crispy color images like the Tokyo subway map shown as Fig. 1. Each color in the image has an important information. But for the color blinds, similar colors cannot be distinguished. If we can convert those colors to different gray values, they can distinguish them. Therefore we try to convert color images to monochrome images. Monochrome images are shown only by brightness such as white, black, and grays. The brightness is called Gray value. When we convert color images to monochrome images, sometimes two different colors are printed with same gray value. In this case we cannot distinguish different colors. In order to convert them, we have to know how many colors are included in a color image. Basic idea of the method is introduced with using a 4-color simple image. If 4 colors are used in a image, we just give white, black, light gray, and dark gray for each color. It looks so easy. However a JPEG image, we usually use this format, includes a number of colors because of its compression way. In the following sections, we show an example image which originally has only four colors. While it is saved in JPEG format, it has 4,483 colors. We show how to reduce the number of colors step by step using it. Finally we can convert it to 4-leveled monochrome image. As an application of the method, we try to treat the part of the Tokyo subway map.