Analysis and design for text readability increase in quad-structure RGBW color EPD

This paper presents a new approach to enhancing the text readability of the quad RGBW color electrophoretic display (EPD). In the color EPD, text characters are jagged due to its low resolution and the jaggedness degrades the readability of the text. However, text characters are usually black-and-white, and for the black-and-white character, it is possible to improve readability by relocating the character sampling points at the sub-pixel level. Based on this, the proposed approach reduces the characters´ jaggedness and enhances the text readability. In implementation, we used two-dimensional contrast sensitivity function and discrete Fourier transform to select the best sampling points. In addition, we applied the proposed method only to text areas after text detection. In the experiments using test images, the proposed method clearly increased the text readability without inducing any visual artifacts in non-text area.